Young plants of Brassica napus (rape), Hordeum vulgare, and Pisum sativum growing in water culture have been exposed to four continuous wind speeds for from 4 to 5 days. The plants were exposed to natural daylight, humidity, and temperature in a wind tunnel in which only air movement was controlled. The wind speeds found among the plants in the four sections of this tunnel were approximately 0·3, 0·7, 1·7, and 4·0 m./sec. The results showed no significant change in relative growth-rate or net as
sinilation rate with wind speed.Previously published results, obtained with plants in soil or sand culture, have differed from those in the present experiments in showing a fall in the amount of growth as wind speed increased. It is suggested that the reduction in growth found in these previous experiments was caused by partial drying out of the plants, whilst in the present experiments water-supply to the roots was abundant and this effect was considerably reduced.
Vegetative plants of Chenopodium amaranticolor were induced to flower by exposure to 2, 6 or continuous short days (SDs) and the effect of such treatments on organogenesis at the apex of the main stem followed by means of dissections. The most outstanding responses to SD treatment were (I) an immediate elongation of the apex, (2) a stimulation of the rate of initiation of leaf primordia, and (3) a promotion of the rate of initiation of axillary bud primordia. In response to as few as 2 SDs, the
rate of initiation of leaf primordia increased from 0.47 to a maximum of 3.70 per day and the rate of initiation of axillary bud primordia immediately increased from 0.47 to 1.35 per day.Precocious initiation of axillary bud primordia led to the formation of double ridges. The results indicate double ridges to be homologous with vegetative axillary buds; although they normally developed into reproductive tissues, they passed through a period of vegetative growth following minimal induction to flowering by exposure to 2 SDs.The rate and degree of flowering were highest in plants which received the longest period of SDs, but the differences in final flowering response were greater than the differences between the initial responses at the apices. The effect of SDs was thus not confined to an initial stimulation of organogenesis; a prolonged exposure to SDs must have enhanced the subsequent development of double ridges into flower primordia.The results are discussed in relation to previous findings and the general conclusion drawn that the initiation of double ridges is very widely accompanied by a stimulation of apical growth. It is suggested that inductive conditions remove a general growth inhibition and that the resultant stimulation of apical growth might lead to the initiation of double ridges.
The morphological nature of the various parts of the lauraceous flower has been discussed on the basis of available evidence from floral anatomy and ontogeny. Evidence from floral anatomy supports the view that both whorls of perianth are homologous and that the inner whorl does not represent modified stamens. The perianth has not attained a level of differentiation into sepals and petals in a real sense. The lauraceous flower might have had staminal appendages in all the four whorls in the ance
stral condition. The living genera represent varying degrees of reduction. These appendages are regarded as modified stamens. The stamens in the family cannot be considered as reduced branch systems. The androecium is interpreted as consisting of stamen fascicles. The two-trace carpel is common in the family. Evidence from ontogeny and vascular anatomy makes it improbable that the gynoecium consists of more than one carpel. The carpel is essentially of the conduplicate type.
Activity of gibberellin-like substances was lacking in leaves of strawberry plants at time of flower initiation, but peduncle elongation was accompanied by significant activity of two substances probably related to GA3 and GA7. Exogenous gibberellin (GAS), applied to strawberry plants at the flower-differentiation stage, strongly promoted peduncle elongation, while similar application of the growth-retardant (2 chloro-ethyl) trimethylammonium chloride (CCC), an inhibitor of gibberellin biosynthe
sis, inhibited peduncle elongation. These treatments also affected subsequent runnering, GA increasing the number of runners, as well as their mean individual length, while CCC caused the opposite effect.
Application of gibberellin immediately after flower-bud initiation, but before peduncle emergence, affected the distribution of fruit yield. GA-treated plants produced more than untreated ones in the first half of the fruiting season, but the situation was reversed in the second half of the season—so that total yields were unaffected. It was suggested that the exogenous gibberellin hastened yield by anticipating the endogenous gibberellin which is normally formed at a somewhat later stage in the plant's development. The parallel responses with regard to elongation of vegetative runners and flower peduncles together with the data of the other experiments seem to indicate that peduncle elongation is a typical vegetative growth response enhanced by gibberellin and checked by substances which inhibit biosynthesis of endogenous gibberellin.
The early stages in the change from vegetative to reproductive development of apple spur terminal buds were followed by dissection of buds from untreated trees, and from trees defoliated at different times in the season. A change in the development of the leaf primordia occurred when there were approximately eight in the bud. This was followed by the development of bracts, which appeared to be necessary for the formation of actual flower parts. Leaf primordia tend to inhibit this process. Wherea
s their effect upon the apical meristem was subsequently reduced by the formation of bracts, so that eventually a terminal flower formed, their effect upon the lower lateral meristems was unaltered. These meristems therefore remained in a vegetative state.In addition to the number of leaf primordia in the bud, the degree of dormancy may be an important factor in determining the onset of flowering. Since the number of leaf primordia in vegetative buds at the end of the season is eight, the spatial distribution of primordia on the main axis of the bud and their vascular connexions might have a decisive effect on bud development. This was related to the effect of older primordia in the bud upon the development of younger ones. In buds in which these older primordia were inhibited by foliage, etc., i.e. those with a long plastochrone, no effects were observed upon the development of younger primordia and the buds remained vegetative.Whilst correlative inhibition of buds thus affected their ability to form flowers, there is no evidence of a critical leaf area for flowering. Flowering in apple buds is more likely to be due to the removal of factors inhibiting reproductive development than to the synthesis of a specific flower inducing substance as such.
The vegetative apex and young inflorescence of Carex flacca have been grown in aseptic culture for several weeks on a defined medium. Explants comprised the apical dome and the three youngest leaf primordia, and the young inflorescence complete with bracts, excised shortly after the initiation of the lateral spikes. Some growth occurred on the basal medium which contained inorganic salts, sucrose, and vitamins, but growth was increased and the life span extended by the addition of certain other
compounds. The most effective additive was gibberellic acid, which, however, resulted in precocious differentiation of the meristematic tissues and the differentiation of abnormal xylem. These deleterious effects of gibberellic acid were counteracted by the addition of kinetin. This substance did not otherwise affect vegetative apices but it resulted in a further increase in growth and life span of inflorescences.
Kleinia articulata subjected to different photoperiods becomes dormant in long days (continuous light) and grows uninterruptedly in short days (8 h). Dormancy results from the rapid cessation of leaf differentiation and expansion. By contrast stem growth is faster in long days and continues until all leaves have died. In long days growth is not halted permanently but flushes of leaf production and stem elongation occur. Resumption of growth is stimulated rapidly by total darkness or short-day tr
eatment of the extreme stem tips for some days. This species is a strict short-day plant in its flowering behaviour, depending on this daylength for normal inflorescence development also.
Flowering was promoted in young plants of Chenopodium rubrum L. by application of growth inhibitors such as 5-fluorodeoxyuridine (FUDR) and (2-chloroethyl) trimethylammonium chloride (CCC), growth substances (indol-3yl-acetic acid, IAA), by the removal of roots and by drought. All the treatments were effective only during the post-inductive period and at the threshold level of photoperiodic induction. The response of plants was strictly time-dependent. The experimental data indicate that the sti
mulation of flowering is usually accompanied by inhibition of leaf initiation and growth. The treatments probably produced variation in the quantitative expression of flowering by causing a shift in emphasis in the development of leaf and bud primordia at the shoot apex. The dynamic analysis of differentiation of the shoot apex indicates a correlation between the morphological stage of the shoot apex and its responsiveness to the treatments.
A cultivar from each of four cereal species (Avena sativa L., cv. Swan, Hordeum vulgare, L., cv. Clipper, Triticum aestivum L., cv. Gabo, and Secale cereale L., cv. South Australian Rye) was grown in controlled environment chambers in a 10-h photoperiod (short days) or 10-h photoperiod supplemented with a 6-h extension by incandescent light. The developmental morphology of the inflorescences was followed to ascertain whether there were any common developmental interrelationships between the spec
ies. Inflorescence internode elongation was initiated when the floret initial first appeared, irrespective of whether it occurred on the most advanced lateral spikelet or on the terminal spikelet of the rachis. The glumes (infertile bracts) of the terminal spikelet of the rachis were initiated when the first second-order inflorescence branch appeared, irrespective of whether the second-order inflorescence branch was a floret initial or a lateral spikelet, as in Triticum sp., or an inflorescence (panicle) branch, as in Avena sp. Cessation of the activity of the apical meristem, as measured by primordium formation, was not correlated with any particular stage of floral development but appeared to be due to a lack of nutrients caused by an increasing competitiveness for the available nutrients from the developing spikelets which are situated closer to the vascular system than the apical meristem.
Whiteness in flowers has been ascribed to reflection of light or to the presence of flavones in the tissue. Light reflection from the surface of chrysanthemum petals and the pigment content of the petals were determined before and after various treatments. After squashing or infiltration of the petals with water, light reflection was reduced to half or less, whereas flavone content remained almost unimpaired. Further reductions in light reflection were obtained by removing the cuticle. An albino
Antirrhinum was white in colour, yet contained no flavone. These results are discussed and it is concluded that whiteness is due to reflection of light, particularly by the surfaces round air spaces.
The morphology of flowering of several cultivars of Dioscorea rotundata, Poir is described. Unisexuality and dioecism occur commonly although complete flowers have been observed occasionally. The pollen grains are sticky and cannot be dispersed by wind; small insects are probably the main agents of pollination. Pollen grain viability appears to be low. Fruit and seed set are also very low and usually not more than five viable seeds are produced on one plant. Production of hybrid plants is feasib
le if filled seeds are selected and germinated following the end of seed dormancy. Seedling development is described from seed germination to the establishment of several leaves on the seedling.
Decapitation stimulated the production of axillary shoots in Arandadeborah. The nature of these axillary shoots, whether vegetative or reproductive, was shown to be correlated with their positions along the stem axis. The higher ones near the apex developed into inflorescences while the lower ones away from the apex developed into vegetative shoots. These results indicated that a flowering gradient exists along the stem axis in this orchid hybrid.
The antigenicity of pollens of 46 species from 36 genera representative of all the major groups of grasses, is examined by immuno-diffusion with antisera to the festucoid Lolium perenne and the chloridoid dactylon. Festucoid grasses show a high degree of immunological similarity with five Lolium antigens, with which grasses from other major groups show relatively little cross-reactivity. Only one Lolium antigen is present throughout the range of grasses tested. Taxonomic patterns are also appare
nt in tests using antiCynodon serum, the antigenic patterns with chloridoids being comparable with and no less complex than those of festucoids with anti-Lollum serum. The taxonomically ordered variation of grass pollen antigens involves both heat-labile and heat-stable (probably allergenic) fractions.
A water deficit imposed during the period of terminal male inflorescence initiation and early development reduced both the growth rate and the mature size of that organ in Zea mays (cv. Iochief). Growth and development of the axillary shoots, the potential female inflorescences, was inhibited during the episode of water deficit but promoted thereafter. As a result, plants which had been subjected to a water deficit at that period produced 2–3 mature cobs and relatively large axillary shoots at t
he lower nodes, whereas plants supplied with water throughout produced a single mature cob and relatively small axillary shoots.A water deficit imposed during other growth phases did not produce this response and, moreover, a further period of deficit imposed later in development, following a deficit at the sensitive stage, inhibited the enlargement of the axillary shoots invoked by the earlier deficit. It did not, however, inhibit the enhanced floral development of those axillary shoots nor reverse the inhibition of tassel growth.The data are discussed in relation to correlative inhibition in Zea mays.
Non-dormant flower initials are laid down in the axils of successive leaf initials as they are formed by the apical meristem of Pisum sativum L. In cultivars with a maximum capability of two flowers per raceme, the undeveloped flower meristem divides into two portions. One forms the first flower and the other either develops into a small protrusion on one side of the first flower or becomes the second flower, depending on the prevailing environment. Flower development in conditions favouring sin
gle-flowered racemes was advanced by one plastochron. Variation in the number of flowers per raceme occurs between cultivars and between environments. The number of double flowers formed was favoured by higher light intensity (120 Js−1 m−2) and carbon dioxide concentration (330 μ11−) and lower temperature (15°C). In cultivars producing more than two flowers per raceme, lower light intensity (60 Js−1 m−2) plus higher temperature (20°C) increased the mean number of flowers per raceme. Soluble sugar levels in all varieties were higher (36.05 mg eq glucose g−1 fresh weight) in the low temperature/high light environment than the high temperature/low light environment (14.80 mg eq glucose g−1 fresh weight).The flowering potential and stability of 13 cultivars have been assessed in controlled environment and in sowing date trials in the field. A stable variety, which consistently produced two flowers per raceme, was identified in controlled environment and its stability was maintained in field trials. A linear regression of stability of flower number in the field on stability in controlled environment accounted for 89.6 per cent of the variance (P<5 per cent), but the flowering potential in a sowing date experiment was not related to temperature or radiation intensity.
Observations and experiments on several species of Musaceae in West Java and Central Sumatra showed that the species with pendent inflorescences are pollinated by macroglossine bats, principally by the long-tongued fruit bats, Macroglossus minimus and Eonycteris spelaea. Among the species with an erect inflorescence M. velutina proves to be self pollinating, while M. salaccensis has sunbirds (Nectariniidae) and tree shrews (Tupaia) as pollinators. A discussion on pollination in this family is pr
The anatomy of pollinated, auxin-induced parthenocarpic and unpollinated watermelon fruits was observed for nine days after flowering. Parthenocarpic fruits were larger and had higher fresh weight and percentage water than pollinated fruits at day 1 but the positions were reversed by day 9. Unpollinated fruits did not increase in size after day 3.
Pericarp cells were small, of regular shape and showed no obvious change with either time or treatment. Cell number increased in the pollinated and pa
rthenocarpic but not in the unpollinated fruits.
Cells divided in the flesh of the parthenocarpic but not of the pollinated fruits which increased in size by cell enlargement only. Starch, present in the cells of the flesh and placenta at day 0 was absent from the unpollinated fruits at day 6.
Ovules grew in both pollinated and parthenocarpic fruits largely due to cell division in the nucellus and integuments; the pollinated ovules were larger than the parthenocarpic throughout. Embryo and endosperm development occurred in the pollinated but not in the parthenocarpic ovules. Starch was present throughout the nine-day period in the integuments of the pollinated and parthenocarpic ovules but was lost from the integuments of the unpollinated ovules by day 6. Pollinated and parthenocarpic ovules contributed increasingly to fruit dry weight over the nine-day period.
It is suggested that the ovule tissues, in particular the nucellus and integument may exert control over early development in both pollinated and parthenocarpic fruits.
Gladiolus has a dry type of stigma. Compatible pollen grains alight and germinate on the receptive surface of the papillae, penetrate the cuticle and grow towards the style through a sub-cuticular pollen-tube guide of mucilage. This is secreted from epidermal cells of the stylodium and style canal. The cuticle, which covers the pollen tube guide mucilage, is continuous through the style canal to the ovary. The wet stigma of Lilium also has cuticular tissue running through the style canal, coveri
Flowers of Digitalis purpurea L. cv. Foxy, take just over a week to develop from the smallest buds and open. Both the anthers and the stigma are closed when the flower opens, the anterior anthers dehisce 2 days after flower opening and the posterior anthers a day later. The stigma opens 2 days later still and the corolla remains attached for a further 2 days.The maximum size of the corolla is reached soon after opening and then remains constant. The fresh weight increases throughout the attached
life of the corolla, whereas the dry weight reaches a maximum at flower opening and decreases during the remainder of the corolla's attached life. The content of antho-cyanin varies greatly from spike to spike. In some spikes the maximum content is at flower opening, in others it is much later, but in all cases the loss of anthocyanin with ageing is very small and the corollas are abcissed without visible wilting or fading. Maximum protein, RNA and glucose contents occur at, or soon after, flower opening and the levels decrease in the corollas as they age. Fructose reaches a maximum at the same time as glucose but does not decrease as rapidly, so that fructose becomes the major reducing sugar in the older corollas. Sucrose cannot be detected in any flowers. Ethylene production increases steadily with flower age, but the maximum production is recorded from flowers which have recently ab-scissed the corolla regardless of whether this occurs before detachment from the spike or within the collection tube.
In a compatible pollination in Crocus, pollen tube tips enter the stigma papillae after the enzymic erosion of the cuticle, and the tubes continue downward growth towards the ovary between the cuticle and the underlying pectocellulosic wall. The cuticle of the receptive zone of the stigma papilla is chambered, the chambers containing a secretion accumulated during the maturation of the stigma. Pollen exudates contain various acid hydrolases, but are incapable alone of eroding stigma cutin. Furth
ermore, there is no penetration when the proteins of the wall-held stigma secretions are degraded enzymically. These facts are taken to indicate that the pollen contributes a ‘cutinase’ precursor which is activated by a factor or factors held in the stigma secretion. Pollens of certain Cruciferae produce tubes capable of penetrating the Crocus stigma cuticle, suggesting that notwithstanding the taxonomic remoteness of Cruciferae and Iridaceae the enzyme activation systems are quite similar.
A generalized equation is derived that relates total dry matter production to time from emergence for crops grown in the field with adequate water and nutrients. It is:w+K1lnw+W0=K2twhere w is the plant dry weight in t ha−1, t is time in days after emergence, K2 and K1 are constants and W0 equals −(w0+K1lnw0) where w0 is the value of w at the start of the growing period.The increases in the dry matter of 18 different types of vegetable crop were measured at intervals during growth in the field.
In every case the data fitted the equation very satisfactorily with K1 set equal to 1 t ha−1. The fitted values of K2 were similar for many crops; those of W0 varied considerably but were always similar to the values calculated from the individual seed weight and the plant population. Good fits were also obtained when time in days was replaced with cumulative evaporation from an open water surface.It is concluded that the growth-time curves of many different vegetable crops can be described by the same simple equation and that the variation between curves can be largely attributed to differences in seed weight and plant population.
The effects of light and temperature on flowering and pollen tube growth were studied in watermelon [Citrullus lanatus(Thunb.) Matsum. and Nakai, cv. Early Yates] plants grown in controlled environment cabinets. All female flowers were pollinated in one group of plants; none was pollinated in the other group.Temperature increase from 25 °C to 35 °C with daylength of 14 h and light intensity of 32 klx caused increase in flower number per plant, proportion of male flowers, ovary length and diamete
r, ovule number per ovary, rate of pollen tube growth and percentage of penetrated ovules at 24 hand 48 h after pollination. Very few flowers were produced at 40 °C, but there was a high proportion of male flowers. Increase in daylength from 14 h to 24 h at 25 °C with light intensity of 32 klx also increased number of flowers per plant, ovary length and diameter and number of ovules per ovary but sex expression and rate of pollen tube growth were unaffected. Reduction in daylength from 14 h to 8 hat 25 °C and light intensity of 32 klx and reduction in light intensity from 32 klx to 8 klx at 25 °C and 14 h daylength both produced an increase in the percentage of immature ovules. The presence of fruit on the vine resulted in fewer flowers per plant and in reduced ovary legnth and diameter under all conditions tested.The results are discussed in relation to the fruiting response of the plant.
The relative assimilatory activity of the inflorescence, its individual components, and the leaves of flowering tillers of Poa annua L. and Lolium perenne L. was determined over the period from inflorescence emergence to seed shedding. The pattern of 14CO2 fixation was similar for both species and the inflorescence was by far the most important assimilatory organ of the reproductive tiller, particularly over the latter period of seed development as leaf senescence progressed. With the exception
of the seeds all parts of the inflorescence showed significant assimilatory activity and the lemmas and paleas accounted for 40–50 per cent of the total 14C fixed by the inflorescence in both species. The importance of the grass inflorescence as a photosynthetic structure is discussed in relation to similar studies on cereals.
This paper is an introduction in the construction technique of models for inflorescence development by means of the theory of L-systems. An inflorescence is thought of as composed of a number of segments. It is shown how for these segments a set of instructions can be formulated and how then, beginning with an initial segment, the whole inflorescence structure can be generated in a number of time steps. The for mation of the flowers and the order of flowering are the two most important features
of an inflorescence pattern and they, therefore, have been most emphasized.
The initiation and development of the flower of Silene coeli-rosa was followed by examining apices by scanning electron microscopy. The sepals, stamens and carpets are initiated in a spiral sequence, the direction of the spiral king the opposite of the acropetal helix of unequal axillary buds at the nodes below the flower. The petals are initiated almost simultaneously and at the same time as the first few stamens. The change in phyllotaxis from opposite and decussate in the vegetative shoot to
spiral in the flower occurs with the displacement of the first two sepals away from the mid-line of the apex and towards the axillary bud at the node below the flower. The sizes of the sepals and stamens are a function of their age since initiation but the petals grow more slowly. The Silene flower can be interpreted as a shoot bearing primordia with associated axillary primordia, some of the latter being precocious in their development.
Pollen dimorphism during the ripening of Nicotiana tabacum anthers takes the form of differentiation at the binucleate pollen stage into normal (N) grains, characterized by their high frequency, larger size, densely–staining cytoplasm and high starch content and into smaller (S) grains characterized by their variable and low frequency and weakly–staining cytoplasm. Most of the S grains show distinctive vegetative and generative nuclei (A grains); a small number have two vegetative–type nuclei (B
grains). Evidence is presented that when excised anthers are cultured, pollen plants arise only from S grains. It is suggested that the differentiation into N and S grains arises by an abnormal second meiotic division in the pollen mother cells.
Previous work has shown that vernalization acts at two sites, one in the cotyledons and one in the shoot, in young plants of genotype Ife Sn Hr. During the present study the size of the vernalization responses in both the cotyledons and shoot increased as the temperature was lowered from 17 to 3 °C. This occurred regardless of whether the treatment was given for the same chronological period of time or for the same physiological period of time. Vernalization treatment was effective from the time
the seeds were developing in the pods on the maternal plant until at least 20 leaves were expanded and became gradually more effective as the length of the treatment was increased from 2 to 5 weeks. High pre– or post–vernalization temperatures can reduce the cotyledon effect and to a lesser extent the shoot effect of vernalization. Devernalization occurred to a larger extent in low light intensities and darkness than in high light intensities. No stabilization of the vernalization effects in the cotyledons or shoot appeared to occur at normal growing temperatures (15–25 °C). These results are discussed in terms of the previously hypothesized mechanisms for the cotyledon and shoot effects of vernalization.
The parental photoperiod appears to have no effect on the flowering node of the progeny, provided the progeny seed is selected to be of the same weight. However, the parental photoperiod does influence the mean seed weight and seed weight is shown to cause significant alterations in the flowering node and time as well as causing alterations in vegetative characters like the internode length and the rate of leaf expansion and node formation. The effect of seed weight on flowering is thought to re
sult from the alterations in the growth rate.On the other hand, vernalization of the parents does appear to cause a small, but significant effect on the flowering node of the progeny (i.e. it could be transmitted through a meiotic division). This effect disappears in the next generation and the possible nature of this effect is discussed.
Modified proliferous flowers arose spontaneously in a small proportion of plants of Silene coeli-rosa growing in garden plots. The modified flowers consisted of leaves, arranged spirally with a mean divergence angle of 138.4° instead of the pentamerous arrangement of the normal flower, and sometimes also carpels which ranged from open structures with exposed ovules to follicle-like structures, free or fused, to fully fused carpels with free-central placentation. In the modified flowers petals an
d stamens were not formed. The primordia at initiation were intermediate in size (relative to the apical dome) between normal leaf and normal sepal primordia but were the same absolute size as the latter. The structure of these anomalous flowers is discussed in relation to the normal flowering process.
There is little information on the fate of embryo sacs in plant ovules if pollination is prevented. In this study embryo sacs from watermelon were observed over a 13 day period following flowering with (a) normal pollination, (b) non-pollination and (c) induction of parthenocarpic fruit development with naphthalene acetic acid. Following pollination, and prior to fertilization approximately 2 days later, the embryo sacs completed development and consisted of two synergids with prominent filiform
apparatus, an egg cell, a central cell with two polar nuclei and three antipodal cells. Sperm nuclei were observed within the embryo sac at 2 days and by 4 days the endosperm was proliferating. In the non-pollination treatment the embryo sac was still intact after 4 days although the antipodal nuclei were becoming hard to distinguish. By 7 days only the two synergids and the egg cell were still well defined, the polar nuclei appeared in some preparations to be fused, and the antipodals had degenerated. By 10 days the embryo sac was a structure-less watery mass. In parthenocarpic fruit the fate of the embryo sac was similar to that in non-pollinated fruit except that final breakdown was delayed past 10 days.Maturity of the majority of embryo sacs in an ovary appeared to be contemporaneous with penetration of the pollen tube, and on the basis of the anatomical results it seems possible that embryo sacs could be fertilized up to 2 days beyond the normal time.
Watermelon ovaries of the varieties Early Yates, Sugar Baby and Candy Red were pollinated, stimulated to develop parthenocarpically with 0.05, 0.5 or 5 per cent 1-naphthylacetic acid (NAA) in lanolin or treated with lanolin alone (control). Pollination produced the greatest number of mature fruits in all varieties but the control treatments produced none. Some fruits reached maturity in response to all levels of NAA in the varieties Early Yates and Sugar Baby. Candy Red produced fewer parthenoca
rpic fruits than Early Yates and Sugar Baby and responded to 0.5 and 5 per cent NAA only. Ovule growth was stimulated in all cases except the controls. In Early Yates and Sugar Baby shrinkage and necrosis of ovules was observed at 21 days after treatment with 5 per cent NAA. In Candy Red little ovule growth occurred and all parthenocarpic ovules were shrunken and necrotic at 21 days after treatment. It is suggested that ovule growth may be important for early parthenocarpic fruit development.
A mathematical model of flowering in Chrysanthemum morifolium Ramat. is described which may be used to predict quantities such as the number of primordia initiated by the apex, plastochron duration and apical dome mass before, during and after the transformation of the apical meristem from vegetative to reproductive development. The model assumes that primordial initiation is regulated by an inhibitor present in the apical dome. Within each plastochron the apical dome grows exponentially, and th
e inhibitor concentration declines through chemical decay and dilution. When the inhibitor concentration falls to a critical level a new primordium is initiated. There is instantaneous production of inhibitor, and a decrease in dome mass corresponding to the mass of the new primordium. The process continues until the apical dome attains a particular mass when the first bract primordium is produced. Subsequent primordia compete with the apical dome for substrates, and the specific growth rate of the dome declines with successive plastochrons. Eventually, the net mass of the dome starts to decline until it is entirely consumed in the production of floral primordia.
The short-day plant Chrysanthemum morifolium cv. Polaris initiated flower buds in all irradiances of continuous light from 7.5 to 120 W m−2. As the irradiance increased, the transition to reproductive development began earlier and the number of leaves initiated before the flower bud was reduced. The autumn-flowering cultivars Polaris and Bright Golden Anne, and the summer-flowering Golden Stardust were also grown in continuous light at different temperatures; all initiated flower buds at tempera
tures from 10 to 28 °C but only the buds of Golden Stardust developed to anthesis and then only at 10 and 16°C. Flower initiation began earliest at 16–22 °C, and the number of leaves formed before the flower bud was increased at 28°C. Golden Stardust was exceptional in that the number of leaves formed was also increased at 10 °C. Axillary meristems adjacent to the terminal meristem initiated flower buds rapidly at 10 °C but not at 28 °C in all three cultivars. These results are discussed in relation to the autonomous induction of flower initiation and the effects of the natural environment on flowering of chrysanthemum.
The growth of the flower and its constituent parts was measured in Silene coeli-rosa plants, induced at 13, 20 and 27 °C, in order to try and identify those processes which consistently occurred and would therefore be more likely to be essential for flower formation.The increased growth rate of the apical dome just before or about the time of sepal initiation was not maintained in the flower, the growth rate of which was comparable to that of a vegetative apex until all the carpels had been init
iated, when it decreased further. The primordia of the same whorl all had similar growth rates so that the relative sizes of the primordia reflected their relative ages since their initiation. The relative growth rate of the stamens was the same (13 and 20 °C) or less (27 °C) than that of the sepals, but the relative growth rate of the petals was lower than either. The growth rate of the flower axis was least at the sepal node and increased both distally and proximally from this region.The plastochron during sepal initiation was shorter than for leaf initiation and tended to be shorter still during initiation of stamens and petals. Increasing temperature increased the rate of primordial initiation but at 27 °C the growth rates of the primordia were lowest although the rates of primordia initiation were highest. The form of the flower, as exemplified by the relative sizes of the primordia at the moment when all carpels had been initiated, was constant despite the differing growth rates and sizes of the primordia on initiation in different temperatures. It is concluded that neither the initiation of the primordia in the flower nor the form of the flower is determined primarily by the relative growth rates of its component parts.
Daily analysis of anther samples during flower development has enabled an estimation of the duration of defined developmental periods in pollen of the grass Phalaris tuberosa. A similar sequence of pollen development has been established for ryegrass, Lolium perenne, where changes in activity of wall enzymes have been followed using quantitative cytochemical methods. Acid phosphatase, an intine enzyme, showed two periods of activity: during the vacuolate period corresponding to deposition of the
intine polysaccharides; and in the maturation period corresponding to cytoplasmic activity. Non-specific esterase showed greatest activity in the parietal tapetal cells until their dissolution early in the vacuolate period when an increase in pollen-associated activity occurred. These changes provide additional evidence for the transfer of tapetal proteins to exine sites.
Plants of Corchorus olitorius, a short-day plant, were subjected to varying numbers of short-day cycles before transfer to long days. Treatments started after germination of the seeds at the time of cotyledon release. Four short-day cycles (10 h natural daylight followed by 14 h darkness) were sufficient to induce flowering in all plants. The number of flowers and fruits produced on a plant increased as the number of short-day cycles was increased from three to 30. Plants given three to seven sh
ort-day cycles produced flowers on the main stem only but when plants were maintained in short days for longer periods, flowers were also produced on the branches. The growth in d. wt of fruits was greatest when plants were maintained in short days throughout.
Seed production, germination and plant growth form were studied in several species of Veronica. The objectives were to compare the reproductive strategies of annual and perennial species of Veronica which varied in their habitats and aggressiveness as weeds. ‘Reproductive effort’ was fairly similar for both annuals and perennials, falling within the commonly observed range for annual species. Seed number per capsule and the 100-seed weight were unaffected by the growth conditions but plant growt
h form was substantially modified in V. agrestis. The small-seeded Veronica species required light for germination and the winter annual V. hederifolia germinated much more vigorously after a low temperature treatment. The growth form, vigour and extent of adventitious root production and rapid seed germination of V. persica must be significant factors in the spread and establishment of this species.
Apical senescence was examined in a range of intact and deflowered flowering genotypes under both long and short photoperiods. The flower inhibitor produced by the gene Sn, appears to have a direct effect on apical senescence since it can delay apical senescence under short day conditions in the absence of flower and fruit development or where the rate of such development is the same in different treatments. Gene Hr can magnify this effect. Gene E, on the other hand, appears to influence apical
senescence only indirectly through the effect it has on flower and fruit development. The flowering genes at the If, sn and hr loci are also thought to have indirect effects on apical senescence. Even in deflowered plants apical senescence appears to occur eventually in continuous light in all genotypes tested indicating that the presence of developing fruits, although promotory, is not essential for apical senescence.
Tussocks of three clones of the perennial grass Deschampsia caespitosa were exposed to natural temperatures, for successive periods with increments of one week, throughout each season in four consecutive autumn/winter seasons. After exposure they were returned to a warm, illuminated glasshouse and the incidence, intensity and timing of flowering were recorded.The year-to-year variations in exposure time requirement for full flowering were very highly correlated (r2 > 0.98) with mean air temperat
ure in the period between mid-September and early December. The relationship with the natural logarithm of accumulated air temperature was similarly good. Daily mean air temperature was also demonstrated to be a good indicator of daily mean tussock temperature (r2 = 0.91), in a series of measurements in the autumn of 1976.More prolonged exposure increased the proportion of apices in a tussock which flowered, but the maximum value at the end of a whole winter was only about 15 per cent. The cumulative vernalization effects of naturally fluctuating temperature regimes are analysed and the significance of these findings for the maintenance of perenniality in clonal grasses is considered.
Populations of four co-habiting annual grass species Bromus mollis L. (Soft brome), Hordeum hystrix Roth (Mediterranean barley grass), Lolium rigidum Gaud. (Wimmera ryegrass) and Vulpia bromoides (L.) S. F. Gray (Squirrel-tail fescue) were examined for the presence and comparative levels of vernalization and photoperiod response. This was evaluated as the number of days from sowing to heading in both long (16 h) and short (normal, over-winter) photoperiods at two levels of temperature.Wide varia
tion among the species in both vernalization and photoperiodic response was detected. L. rigidum possessed a high level of vernalization response and was comparatively sensitive to photoperiod while V. bromoides possessed little or no vernalization response and was comparatively insensitive to photoperiod. B. mollis and H. hystrix appeared to be intermediate between these two species for both responses. There were wide differences in time to heading under long photoperiod (16 h) and high temperature (20 °C) of plants derived from seed of three of the species ripened under non-vernalizing temperatures. This variation indicates the likely existence of genetic differences in vernalization response between plants of these populations.The implications of these findings to the adaptability of these species to the Australian environment have been outlined.
The canal that traverses the upper part of the style of Trifolium pratense is derived lysigenously. The core tissue of the very young style consists of elongated cells similar to those of the transmitting tissue of solid-style families such as the Solanaceae; as the style matures, these cells separate to form the canal, which receives secretions both from the core tissue and the inner wall cells. The early secretion of proteins into the intercellular spaces is associated with the presence of par
amural bodies (lomasomes) in the adjacent cells. In the cells in the immediate vicinity of the canal, vesicles, probably derived from the Golgi system enlarge during later development and accumulate a protein-carbohydrate content, which is later passed into the cytoplasm where it forms densely packed fibrillar nodules. With the dissolution of the cell membranes, this material is passed into the canal, where it is progressively diluted by continued ingress of water until the cavity reaches its final volume.
Structurally preserved angiosperm flowers are described from the Upper Cretaceous of southern Sweden. They are found in fluviatile deposits dated, on palynological evidence, as Upper Santonian or Lower Campanian. The material studied includes two species of Scandianthus gen.nov. and one unnamed, related taxon. The fossil flowers represent the best-preserved Cretaceous floral structures available and the preservation permits detailed study of organization and arrangement of parts. Comparison with
flowers of extant angiosperms indicates a close relationship with members of the Saxifragales.
Flower formation in Liatris spicata Willd. was not affected by photoperiodic treatments, but long days (16 h) had a pronounced effect on elongation of the flowering stem. An illuminance of 2 Ix was sufficient to produce near maximal elongation.Long days caused a decrease in endogenous gibberellins in the tips of rapidly elongating stems and decreased the number of flowering stems per corm.
The intact stigma of Trifolium pratense possesses a smooth receptive surface fringed by a few ranks of brush hairs. This surface is ensheathed by a thin (75–100 nm) but highly impermeable cuticle, which encloses four to five ranks of secretory cells immersed in their secretory products. Experimental single-grain pollinations show that pollen cannot become hydrated or germinate on the intact surface. The cuticle is ruptured when the flower is tripped; the secretion is released, and captured polle
n-self or cross-can then germinate. As in other papilionoid Leguminosae, this mechanism provides a guard against premature selling. The secretory cells are elongated; they remain in communication through persistent pit-fields as the intercellular spaces fill with secretion product. The secretion forms a lipid-rich emulsion, with a mucilaginous aqueous phase which reacts cytochemically for protein and carbohydrate and has esterase activity. During the early development of the stigma head, the cells possess a fine-structure appropriate to their secretory function, with abundant ribosomal and smooth endoplasmic reticulum, stratified or in the form of ramifying and anastomosing tubules, numerous mitochondria and a well developed Golgi system. Lipid globuli, partly invested in endoplasmic reticulum, are abundant in the young cells, but there is as yet no indication of how the lipid is transferred to the intercellular spaces during the secretory period. As the stigma matures, the secretory cells become moribund.
Dormancy was induced during storage of Liatris spicata corms grown in Israeli summer conditions, but plants left in soil continued vegetative growth. Corms of winter-grown plants sprouted freely. Treatment with GA3 restored both sprouting and flowering in summer-grown corms, but in winter corms GA2 was effective only after corms were stored at low temperature. All the plants flowered after 4 weeks at 2 °C and GA3 treatment.The content of gibberellins in the main bud of freshly excavated corms de
creased during the first 18 d of storage but increased to the initial level after 4 months of cold storage. The number of flowering stems increased to 2.5 per corm when corms were cold-stored up to 75 d, but decreased with a longer storage.
Stomatal sensitivity to water stress was investigated in pearl millet [Pennisetum americanum (L.) Leeke] in relation to stage of plant development, leaf water status and ABA content by sampling plants at midday. For the same leaf water potential (ψ), droughted plants with emerged panicles were found to have a greater leaf conductance (gL), indicative of greater stomatal opening, than plants sampled prior to panicle emergence. The difference between such flowering (F) and non-flowering (NF) plant
s in ψ at stomatal closure was estimated to be at least 0.6 MPa. This difference was considered unlikely to be the result of differential bulk leaf osmotic adjustment, and for most samples from both F and NF plants, bulk leaf turgor potential (ψp) was estimated to be zero.Stomatal closure in NF plants was associated in two genotypes (BJ 104 and line 112) with higher leaf ABA levels. Differences in ABA levels between F and NF plants were, however, smaller or absent in genotypes Serere 39 and B282. These genotypes were at lower ψ than BJ 104 and line 112 when sampled and showed smaller differences between F and NF plants in conductance.Lower ABA levels in F plants are ascribed either to effects of leaf ageing or to effects of flowering on ABA content of the leaf. Significant differences in gL in the absence of differences in ABA content are taken to imply changes in stomatal sensitivity to the hormone or in its access to the stomatal complex.
The anther in Ophiorrhiza is dithecous and tetralocular, its development being of the dicotyledonous type. The anther wall comprises epidermis, endothecium, middle layer and secretory tapetum. The pollen grains are tricolpate and triporate. The microspore nucleus undergoes division to form a vegetative nucleus and a generative nucleus and protrusions (pollen buds) are formed from the germ pores after the first division of the microspore nucleus. The vegetative nucleus moves into one of these bud
s or first breaks into a number of irregularly sized nuclear particles which enter into one, two or into all three buds, where they degenerate. Then the pollen buds are separated and the generative nucleus divides inside the pollen tube to form two sperms.
Petunia hybrida and Lilium lankongense pollens were germinated on thin layer chromatography (TLC) plates following chromatography of extracts from the self-, cross- and unpollinated stigmas, styles and ovaries and the seeds, leaves and pollen of three inbred Brassica oleracea families. Zones of pollen germination inhibition on the TLC plates showed that inhibitory compounds were present in the tissue extracts. The Rf values and number of these compounds varied with the tissue used, stigma tissue
containing the largest amounts and the greatest number of inhibitors. In contrast, differences between the inbred lines tested were slight and quantitative. Pollen from both P. hybrida and L. lankongense gave the same results; that from B. oleracea could not be used because of its poor germination.
The development of the one and-inline of the pollen wall are described for Gibasiskarwinsk yana and G.venustula. During the tetrad stage the appearance of electron-opaque depositions or tri-partite plates at discrete sites between the plasma membrane of the spore and the inward surface of the callose special wall are the first indications of exine development. The sulcus rapidly differentiates being composed of discret
e exine granules on a thin foot layer. Probacula in non-apertural areas develop in an electron-opaque granular layer situated between the plasma membrane, which is highly convoluted, and the callose special wall. A foot layer is formed from electron-opaque lamellae at the plasma membrane. Exine pattern is clearly established within the tetrad. After release of the spores from the tetrad an intimate association is rapidly developed between the plasma membrane of the periplasmodial tapetum and the newly-formed exine. Compacted electron-opaque material is found at the interface between membrane and the exine and vesicular material is added from the tapetum. The increase in volume that occurs in both spore and anther is accompanied by considerable vacuolation.Intine development begins just prior to pollen grain mitosis and continues rapidly at the aperture. The thin foot layer becomes discontinuous. Further intine deposition takes place after mitosis and a bilayer is apparent in mature grains. The matrix of this layer contains conspicuous electron-opaque platelets. The exine of the mature spore stains less intensely than in the young spore and the interbacula spaces are filled with material from the degenerate tapetum.
In addition to the known loci, If, e, sn and hr, a fifth locus, veg, is shown to control flowering in peas. Regardless of the genotype for the other flowering genes, plants homozygous for the gene veg did not initiate flower buds under a wide range of photoperiod and temperature regimes, including those normally highly promotory in peas. Treatment with various plant growth substances and grafting to stocks known to promote flowering also failed to cause initiation. Gene veg prevented expression
of allelic differences at the If locus but segregation for alleles at the sn and hr loci was clearly visible by examination of several vegetative characteristics. For example, sn hr veg and Sn hr veg plants showed an opening of the apical bud, production of lateral branches, and a reduction in growth rate, leaflet size, internode length and stem thickness at approx the same time as sn hr Veg and Sn hr Veg plants carrying the Lf allele commenced fruit production, respectively. The graft-transmissible inhibitor controlled by gene Sn is therefore not specific for the transition from vegetative to reproductive growth. Gene veg allows the processes leading to apical and foliar senescence to be examined independently of any effect of flowering and fruiting. We found that gene Sn influenced the total number of leaves expanded in veg plants but not the time of shoot senescence, which, in plants without flowers and fruits appeared to result from failure of the root system.
The development and cytochemical features of the stigma and style have been investigated in Sugar apple, Annona squamosa L., using light and electron microscopy. The pistil is a syncarp with an open stylar canal. Papillae of epidermal origin line both the surface of the stigma and the inner face of the stylar canal. The papillae contain organelles characteristic of secretory cells with a highly thickened cellulosic wall. The wall is multi-layered, the zones differing in their microfibrillar stac
king and orientation. The stigma is of the ‘wet’ type and the surface exudate is heterogeneous in microscopic appearance and reacts cytochemically for proteins, carbohydrates and lipids. The surface cuticle undergoes dissolution prior to anthesis. A secretion also appears in the thickened middle lamella of the sub-epidermal cell layer which reacts cytochemically for pectinaceous acidic polysaccharides.Esterase activity of papillae is indicative of the receptive areas, and it is also related to the onset of receptivity. Acid phosphatase activity is intense in the sub-epidermal cell layers which probably reflects their secretory activity. Pollination triggers a copious flow of secretion onto the stigma surface which engulfs the pollen grains. It appears that most of the acidic polysaccharides of this secretion come from the middle lamella of the sub-epidermal cell layer.Compatible pollen tubes have no apparent barriers to overcome on their route to the embryo sac and the inherent protogynous dichogamy seems to control the acceptance or rejection of compatible pollen.
In the mature Brassica pollen grain, the outermost wall layer, the exine, is surrounded by a trilamellar structure which presents some of the morphological, cytochemical, enzymological and physico-chemical characteristics of a biological membrane. This structure, designated the exinic outer layer (EOL), has been visualized and partially characterized by electron microscope techniques. Its possible involvement in the male-female recognition reaction is discussed.
When plants of Impatiens balsamina L were subjected to 5 short days and then re-placed in long days, they began to form a terminal flower and then reverted to vegetative growth at this terminal shoot apex The onset of flowering was accompanied by an increase in the rate of initiation of primordia, an increase in the growth rate of the apex, a change in primordium arrangement from spiral to whorled or pseudo-whorled, a lack of internodes, and a reduction m the size at initiation of the primordia
and also of the stem frusta which give rise to nodal and internodal tissues On reversion, parts intermediate between petals and leaves were formed, followed by leaves, although in reverted apices the size at initiation and the arrangement of primordia remained the same as in the floweing apex The apical growth rate and the rate of primordium initiation were less in the reverted apices than in floral apices but remained higher than in the original vegetative apex Since the changes in apical growth which occur on the transition to flowering are not reversed on reversion, the development of organs as leaves or petals is not directly related to the growth rate of the apex, or the arrangement, rate of initiation or size at initiation of primordia
Factorial combinations of five photoperiods (8 h 20 min, 10 h, 11 h 40 min, 13 h 20 min and 15 h) and three night temperatures (14, 19 and 24 °C) combined with a single day temperature (30 °C) were imposed on nodulated plants of nine soya bean genotypes [Glycine max (L.) Merrill] grown in pots in growth cabinets. The times to first appearance of open flowers were recorded. For a photoperiod-insensitive cultivar, and for the remaining eight photoperiod-sensitive genotypes in photoperiods shorter
than the critical daylength, the rates of progress towards flowering (the reciprocals of the times taken to flower) were linear functions of mean diurnal temperature. For all photoperiod-sensitive genotypes, times to flowering in photoperiods longer than the critical daylength increased as inverse functions of both increasing photoperiod and decreasing temperature. A consequence of these two relations is that the critical daylength becomes longer with higher mean temperatures. In the five photoperiod-sensitive genotypes which flowered in all environments before the experiment was terminated (after 150 d) the delays in flowering due to low temperatures or long photoperiods were limited by a maximum period to flowering specific for each genotype. These results are discussed in relation to the development of a simple technique for the large-scale screening of soya bean germplasm to determine photo-thermal response surfaces for flowering.
Floral initiation in seedlings of Stylosanthes guianensis var. guianensis cv. Schofield grown at a photoperiod marginal for flowering (12−11.75 h) was promoted by a combination of low day (25 °C) and low night (16 or 21 °C) temperatures, and completely inhibited by a 35 °C day temperature. Additionally, earliness of floral initiation under naturally decreasing daylength was negatively related to temperature regime over the range 35/30 to 20/15 °C (day/night).
As in other papilionoid Leguminosae, the receptive surface of the stigma of Viciafaba L. is invested by a detached cuticle. This cuticle, the so-called 'stigma membrane' of plant breeding literature, is lifted away from the epidermis during development by the accumulation of a lipid-rich secretion released into the intercellular spaces of the stigma head by the epidermal cells and the underlying three to four cell layers. The cuticle is thickened over the prom
inences left by the epidermal papillae, thinning out between. Pollen, whether self or cross, cannot hydrate and germinate in contact with the intact stigma surface, but must await the disruption of the cuticle and the release of the retained secretion. In most genotypes this takes place only when the flower is tripped by visiting pollinators or in consequence of severe agitation by wind. A comparison of lines differing in their degree of autofertility in field conditions has revealed various differences in stigma structure. A highly autofertile line had low papillae at the receptive tip, with a relatively thin intervening cuticle, while an autosterile line had longer papillae and a thicker cuticle. A line with partial autofertility was intermediate in these characteristics. These properties of the stigma surface, together with other differences in flower structure, are probably adequate to account for the variation in the degree of autosterility, since no evidence was obtained suggesting the presence of an effective physiological self-incompatibility system in any of the lines studied. Since the rupturing of the stigma cuticle is affected by the turgor pressure of the cells of the stigma and style, some degree of environmental interaction is to be expected: autofertility should be at the highest in conditions of adequate water supply, and lowest where there is water deprivation.
In controlled environment, the effective pollination period in Larix leptolepis is characterized by its brevity, lasting for less than 1 d. It is associated with the opening of the papillae of the pollen collecting apparatus which possess surface esterase activity, a condition that has its parallel in the surface pellicle of angiosperm stigmas.
The stigma in Zephyranthes candida and Z. citrina is of the dry type with a continuous cuticle—pellicle. In some papillae, however, the terminal portion of the cuticle—pellicle is lifted upwards and occasionally even disrupted by the accumulation of a secretion product below it. Both non-specific esterases and acid phosphatases are present on the stigma surface. The style is solid with a central core of transmitting tissue which has conspicuous intercellular spaces containing a matrix that inclu
des proteins, polysaccharides and pectic substances.Zephyranthes citrina is self-compatible while Z. candida is self-incompatible. Followng incompatible pollination in Z. candida, pollen germination is normal but pollen tube growth is inhibited at the junction of the stigma and style. Self-incompatibility can be overcome by bud pollination. Protein synthesis is necessary for pollen germination in both species. Concanavalin A binds to the stigma surface of both species, but does not affect pollen tube penetration in Z. candida. In crosses between the two species typical unilateral incompatibility is observed when Z. candida is used as the pistillate parent.
In the sweet pea (Lathyrus odoratus L.) the difference in floweringbehaviour between photoperiodic (long-day) and day-neutral cultivars appears to be due to a difference in their ability to produce a graft-transmissible floral inhibitor. The flowering control systems in the sweet pea and the garden pea (Pisum sativum L.) appear to be very similar on the basis of inter-generic graft results. It is suggested that the major flowering genes Dn* in L. odoratus and Sn and Dne in P. sativum control ste
ps in a biochemical pathway common to these two species (which are related at the tribal level) and that the product of this pathway inhibits flowering and promotes outgrowth of basal laterals in both species.
A sixth major flowering gene, dne, is identified in the garden pea (Pisum salivum L.). Linkage tests show dne is located on chromosome 3 near locus st. The ability to respond to photoperiod depends on the joint presence of the dominant genes Sn and Dne which together confer a long day habit. Genotypes Sn dne, sn Dne and sn dne are all essentially day-neutral although by examining several flowering criteria under strictly controlled conditions some small responses could be demonstrated. Like sn,
dne reduced the response to vernalization when substituted into genotype Sn Dne.It is suggested genes Sn and Dne both control steps in a biosynthetic pathway which leads to the production of a graft-transmissible inhibitor of flowering and apical senescence. Stocks of genotype Sn dne and sn Dne promoted flowering in Sn Dne scions while Sn Dne stocks delayed flowering in Sn dne (and sn Dne) scions. However, reciprocal grafting between genotypes Sn dne and sn Dne gave no evidence of physiological complementarity corresponding to the genetic complementarity ofSn and Dne. Initial results suggest dne may be less effective than sn at blocking inhibitor production but this requires confirmation.
Factorial combinations of three photoperiods (10, 13 and 16 h), two day temperatures (18 and 28 °C) and two night temperatures (5 and 13 °C) were imposed on nodulated plants of six diverse genotypes (cultivars and land-races) of lentil (Lens culinaris Medic.) grown in pots in growth cabinets from vernalized (1.5 ±0.5 °C for 30d) or non-vernalized seeds (i.e. 144 ‘treatment’ combinations). The times from sowing to the appearance of first open flowers were recorded. Vernalization, long days and wa
rm temperatures hastened flowering but genotypes differed in relative sensitivity to each of these factors and in time to flowering in the same most-inductive environment. Rates of progress towards flowering (i.e. 1/f the reciprocals of the times to first flower, f) in all genotypes, vernalized or not, were linear functions of both mean temperature, t¯ , and photoperiod, p, with no interaction between the two terms. So, over a wide range of conditions (covering the photo-thermal regimes experienced by lentil crops world-wide), time to flowering can be described by the equation: 1/f= a + bt¯ +cp, where a, b and c are constants which differ between genotypes and the values of which provide a sound basis for screening germplasm for sensitivity to temperature and photoperiod. Although these two environmental factors affect the same phenological event (i.e. time to flowering) our data suggest the responses are under separate genetic control. Seed vernalization consistently increased the values of both a and b in all genotypes. The implications of these collective findings for the screening of lentil germplasm are discussed.
Effects of temperature on floral initiation of ten white clover varieties growing in controlled environments are described. Plants grown under long days (16 h) were subjected to constant temperatures of 26, 18 and 10 °C. Relationships between morphological and physiological traits and flowering were examined.Most plants flowered at the two higher temperatures but only 10 per cent of plants flowered at 10 °C. Larger leaved types tended to produce more reproductive buds per stolon at the higher te
mperatures than did smaller leaved varieties.Of the floral characters studied, floret number was least affected by temperature. Ovule number and peduncle length were greatest at 18 °C. Variation in, and absolute level of nectar secretion was greatest at the highest temperature.
Factorial combinations of two photoperiods (12 and 15 h), three day temperatures (20, 25 and 30 °C) and three night temperatures (10, 15 and 20 °C) were imposed on nodulated plants of nine chickpea genotypes (Cicer arietinum L.) grown in pots in growth cabinets. The times to first appearance of open flowers were recorded. For all genotypes, the rates of progress towards flowering (the reciprocals of the times taken to flower) were linear functions of mean temperature. There were no interactions
between mean temperature and photoperiod but the longer photoperiod increased the rate of progress towards flowering. These effects were independent of both radiation integral (the product of irradiance and photoperiod) and the vegetative stature of the plant. Taken in conjunction with evidence from work on other long-day species, it is suggested that the photo-thermal response of flowering in chickpeas, over the range of environments normally experienced by the crop, may be described by the equation: 1/f = a+bī+cp in which f is the number of days from sowing to first flower, ī is mean temperature and p is photoperiod. The values of the constants a, b and c vary between genotypes and provide the basis for screening genotypes for sensitivity to temperature and photoperiod.
Three flowering classes were identified amongst Lathyrus odoratus L. cultivars on the basis of response to photoperiod. Class DN is essentially day-neutral and it corresponds to the early (winter) flowering group. Classes LDI and LDH are long day types with an intermediate and high response to photoperiod, respectively. These classes correspond to the Cuthbertson (spring) and late (summer) groups. All classes show a substantial response to vernalization. The classes are most easily distinguished
in short day conditions following four weeks of seed vernalization and these conditions were used to examine segregation in crosses between and within classes. The class differences are determined by three allelic genes, dn, Dni, and Dnh, which in homozygous condition give phenotypes DN, LDI and LDH, respectively. Crosses of the type LDH × DN and LDH × LDI gave discrete 3:1 segregations in F2 in terms of either flowering node or days to open flower. However, Dni showed little or no dominance over dn and segregations of the type Dni/dn gave either continuous trimodal distributions or discrete, 3 class segregations in the ratio 1:2:1.The three classes showed marked differences in branching habit which were apparent well before flower initiation. DN segregates seldom produced laterals, LDH segregates branched profusely from the basal nodes while LDI segregates were intermediate in branching tendency. The alleles at the dn locus also influenced dry matter distribution in the shoot, e.g. compared with DN segregates, LDH segregates had smaller apical buds, leaves and main shoots but a greater weight of lateral branches. It is suggested the primary role of the Dnh (Dni) product may be to direct assimilate flow.
Impatiens balsamina L. was induced to flower by exposure to 5 short days and then made to revert to vegetative growth by return to long days. After 9 long days reverted plants were induced to re-flower by returning them to short days. Petal initiation began immediately and seven primordia already present developed into petals instead of into predominantly leaf-like organs. However, the arrangement of primordia at the shoot apex, their rate of initiation and size at initiation remained unchanged
from the reverted apex, as did apical growth rate and the length of stem frusta at initiation. The more rapid flowering of the reverted plants than of plants when first induced, and the lack of change in apical growth pattern, imply that the reverted apices remain partially evoked, and that the apical growth pattern and phyllotaxis typical of the flower, and already present in the reverted plants, facilitate the transition to flower formation.
The volume of the floret cavity at different floret positions along the spike and within a single spikelet was estimated in 10 Triticum aestivum and three T. durum lines by injecting floret cavities with liquid silicone rubber which solidified thereafter. Highly significant correlation coefficients, ranging from 0.40 to 0.76 were found between floret volume and grain weight; in most lines the basal florets had a higher correlation than the terminal ones. The relationships between floret volume a
nd grain weight were characterized by an intercept of about 30–60 per cent of the mean grain weight (heavy-grained lines having a larger intercept) and a slope of about 1 mg μI−1. Differences in grain size and shape, both within spike as well as among lines, closely reflected the variation in the size of floret cavity. The data support the hypothesis that grain weight is partly determined by the volume of the floret cavity.
The urn-shaped flowers of Acrotriche serrulata R.Br. are unusual in two features: the mode of pollen presentation, and the corolla tube which is filled with nectar at maturity, submerging the style and stigma. At the end of the corolla tube, the petal lobes bear conspicuous subterminal hairs that usually contain clumps of pollen embedded in viscous pollencoat materials. Developmental studies show that at anthesis, pollen from the dehisced anthers adheres to the petal hairs. When the corolla lobe
s reflex, the pollen is presented on the newly exposed hairs. The mature corolla tube either abscises or may be removed by nectar-seeking non-flying marsupials, putative agents of pollination.
The response to different combinations of daylength (14, 15 and 16 h) and day/night temperature (20/10°C, 30/15°C) of four white clover (Trifolium repens) varieties in terms of floral initiation and development was studied.More plants flowered under long days (16 h) at 30°C than in any other combination. Varietal differences in response to daylength were large but temperature was the factor controlling initiation.Daylength was more important in regulating peduncle length, floret and ovule number
s than was temperature. The amount of nectar produced was lowest at the higher temperature although nectar concentration was unaffected by temperature. Nectar concentration was lowest in the shortest daylength (14 h).
Senescence of flowers of Petunia hybrida Vilm. cv Gypsy is characterized by colour changes, wilting and abscission. In emasculated detached flowers the onset of these processes is hastened by any treatment which reduces the vigour of the stigma. Thus pricking it, excising segments, or freezing with liquid nitrogen all reduce the time to morphological changes associated with corolla senescence. Removal of the stigma has the most dramatic effect, reducing lifespan of the flower by about 50 per cen
t, to 3 d. This reduction can be lessened if IAA or 2,4-D is applied to the cut surface of the style. In intact flowers, the style may usually be implicated in the production of a stimulus leading to corolla abscission, but abscission will also occur in the absence of the style. Some senescence acceleration takes place not only in the complete absence of the style, but also when the upper part of the ovary has been excised in addition. The speeding up of senescence and of corolla abscission cannot be due solely to damage per se since when the corolla limb was excised, leaving only the corolla tube, the tube abscised at about the same time as the controls, despite the quite extensive wounding. This also implies that the distal parts of the corolla do not play a major role in the development of the abscission zone at the base of the corolla tube.A healthy, undamaged stigma appears to be very important in corolla longevity and one of its roles may be to prevent the production of an abscission/wilting stimulus by some other component of the flower. Possibly auxins in the stigma are important in that either they are mobile and protect the abscission zone or they create a sink for other substances which are implicated in flower senescence.
The structure and ultrastructure of the extrafloral nectaries of Sambucusnigra L. were studied. These nectaries are stalk-like and occur at the bases of the leaves and leaflets. The nectariferous tissue occurs at the top of the nectary and is continuous with the single central vascular bundle. The nectariferous cells have a dense cytoplasm and contain a well developed endoplasmic reticulum. With the commencement of nectar secretion disintegration of the nectariferous
cells takes place. This process starts at the summit of the nectary and proceeds downwards. The question as to whether the process of secretion is holocrine or merocrine is discussed.
The reproductive biology of flowering plants is one of the most rapidly developing fields in plant science, due largely to the introduction of new molecular and computer technology. Today, the techniques of cell biology have new implications for plant reproductive success. This success can be estimated using measurements of pollen quantity and quality, pollen germination and tube growth, and successful fertilization. The complex array of interrelated processes constituting reproductive success i
s a focus for plant biologists who need to understand, modify and exploit them for plant improvement. The success of fertilization is reviewed in terms of (1) differential gene expression in pistil and pollen, and (2) effectiveness of the gametes. On the female side, potential genes of interest include those regulating stigma receptivity, self-incompatibility and ovule viability. On the male side, interest centres on molecular analysis of certain pollen-specific genes which affect male transmission at fertilization. Experimental analysis of the effectiveness of the male and female gametes is being approached in two distinct ways: (1) analysis of their nature and organization using image analysis combined with interactive computer graphics, and (2) isolation of the gametes using cell fractionation technology. Examples of these approaches are given for sperm cell biology, where there are two important questions to be answered: (1) what is the organization of the pair of sperm cells and their delivery system within the pollen tube? and (2) is there specific recognition between the sperm cells and the female gametes — the egg and central cell?
Petunia corollas wilt and abscise between one and two weeks after detachment when maintained in distilled water in vials at 18 °C. The onset of wilting is brought forward substantially by the application of 1-aminocyclopropane-1-carboxylic acid (ACC) either to the vial solution or to the stigmatic surface. Both pollination and stigma removal also shorten the time to the onset of wilting, colour change and to abscission. In the case of stigma removal, the life span of the corolla is shortest when
the treatment is made at the time of flower detachment (day 0), whereas pollination has the greatest effect if it occurs on day 1. Stigma damage still has an effect on corolla senescence even when stigma and style are removed, as long as they have been left in place for a few hours after treatment. Evidence from several experiments shows that a 17 h period is sufficient for the full effect to be shown, and that probably there are some effects on the corolla even if the damaged stigma is only left in position for 3–6 h. Treatments which advance corolla death (to day 3) also advance the peak of ethylene production by the pistil (to day 1) and the corolla (to day 2). The use of silver thiosulphate (STS) overcomes all manipulative and chemical treatments used, and greatly extends vase life. The extension occurs even when STS application is delayed for 24 h, i.e. after the peak of ethylene production by the pistil and after any senescence signal has arrived at the corolla. In this case, however, the time to first morphological change is largely unaffected, but the STS greatly extends the time period between first morphological change and corolla death. The evidence suggests that early symptoms of senescence e.g. colour change and slight loss of turgor, do not automatically lead to corolla abscission.
Embryo sac development has been investigated in unpollinated, cross pollinated and gibberellic acid (GA2) treated flowers of Pyrus communis L. While pollination and GA3 treatments do not alter embryo sac development, they prolong embryo sac viability. In untreated unpollinated flowers, ovules degenerate between 12 and 21 d after anthesis, while in cross pollinated and GA3 treated flowers this degeneration is postponed by about 10 d. Thus, in a cross pollinated flower this extends the period over
which a successful fertilization can take place. This increased period of viability is accompanied by an elongation of the embryo sac itself. Elongation takes place two weeks prior to fertilization in cross pollinated flowers.The extension of life span of embryo sacs following pollination and treatment with gibberellic acid indicates that a stimulus induced by ‘pollination’ could be mediated by GA3 Whatever its mechanism of operation, the prolongation of embryo sac viability by pollination represents a selective advantage, in that the period at which the ovules are receptive to fertilization must be significantly extended.
The effects of day-length and temperature on flowering and dormancy induction were studied in Anemone coronaria L., with plants raised either from corms or achenes. An Israeli hybrid source was used (de Caen cv. Hollandia × Israeli wild type).Dormancy onset is characterized by the cessation of foliage leaf production, the appearance of leaf scales protecting the perennating bud, and leaf senescence. Dormancy was induced by high temperature and long days but increasing temperatures (from 17/12 °C
to 32/12 °C) induced earlier dormancy than prolonging the photoperiod (range 8–16 h). A significant (P = 0.01) interaction was found between these factors, with smaller photoperiodic effects the higher the temperature. At 22/17 °C the critical day-length for dormancy induction was between 11 and 12 h.The transition from the vegetative to the reproductive stage appears to be an autonomous process that occurs with development in plants raised from either corms or achenes and does not require environmental induction. Photo- and thermoperiodic effects on flowering were indirect, being mediated through their influence on dormancy induction.
One cultivar and one land-race of faba bean were subjected to 18 potentially vernalizing pre-treatments (constant temperatures of 1, 5 or 9 °C factorially combined with photoperiods of 8 or 16 h d−1 for 10, 30 or 60 d), and then transferred into four different growing regimes (‘day’/‘night’ temperatures of 18/5 °C or 24/13 °C factorially combined with photoperiods of 11 or 16 h d−1). Control plants were grown entirely in the latter four regimes. The times from sowing to appearance of first open
flowers were recorded for all plants. Control plants of the land-race Zeidab Local flowered sooner in long days and in the warmer regime. Pre-treatment reduced the subsequent time to flower in the four growing-on regimes but most of the variation in the total time to first flower for the pre-treated plants was accounted for by differences in the combined photothermal time accumulated in the two successive environments - which was predicted by a simple photothermal model. Thus, there was neither a specific low-temperature nor a short-day vernalization response in this accession. Similarly, no true low-temperature or short-day vernalization response was detected in the cv. Maris Bead. However, this UK cultivar flowered later than predicted in the 24/13 °C regime, indicating that the 24 °C ‘day’ temperature was supraoptimal. Delays to flowering at 24/13 °C were, however, less evident when plants were grown in long days or following prolonged (30–60 d) pre-treatments at cool temperatures.
Factorial combinations of three photoperiods (10, 13 and 16 h), two day temperatures (18 and 28 °C) and two night temperatures (5 and 13 °C) were imposed on nodulated plants of six diverse genotypes of faba bean (Vicia faba L.). Plants were grown in pots in growth cabinets from both vernalized (1.5±0.5 °C for 30 d) and non-vernalized seeds. The times from sowing to the appearance of first open flowers (f) were recorded. Seed vernalization decreased the subsequent time taken to flower in almost a
ll genotype x growing environment combinations (the exceptions were plants of the cv. Maris Bead grown in three cooler, short-day regimes). The influence of temperature and photoperiod on the rate of flowering was quantified, using a model applied previously to other long-day species of grain legume in which positive linear relations between both temperature and photoperiod and the rate of progress towards flowering are assumed to apply. A significant positive linear response of rate of progress towards flowering to limited ranges of mean diurnal temperature was detected in all six genotypes, but in three genotypes (Syrian Local Large, Aquadulce and Maris Bead) the 28 °C day temperature reduced the rate of progress towards flowering - suggesting that the optimum temperature for flowering in these genotypes is below 28 °C. In four genotypes (Maris Bead, Giza-4, Aquadulce and BPL 1722) a significant positive response to photoperiod, typical of quantitative long-day plants, was observed only in plants grown from vernalized seeds. In contrast, plants of the genotype Zeidab Local grown from both non-vernalized and vernalized seeds showed the same positive response to photoperiod, whereas plants of the land-race Syrian Local Large were consistently unresponsive to photoperiod. The implications of this range of responses amongst diverse genotypes are discussed in relation to screening germplasm.
Tissue-invasive pollen tube branching occurs in an Australian shrub, Grevillea banksii R.Br. (Proteaceae). Parenchyma and phloem of the ovary wall are soon infiltrated after fertilization, by intercellular branches and the lumina of xylem elements are entered. Ovular tissues are not affected.
A convenient measure of biological and, in special cases, physical age is the plastochron (P) or the plastochron index (PI). The basic concept can be generalized and also be applied to any strictly modular system as well as to its modules. However, differing values will be assigned to modules arising from modular systems of different ‘relative developmental density’. For instance, if one modular system (e.g. a shoot or an infloresence) produces more modules (e.g. leaves or flowers) than an other
during development between two independently-defined reference stages, then modules of equal developmental status differ in their plastochronal ages. This problem is avoided by reference to the normalized-age concept, using the ‘normalized-plastochron’ (NP) and the ‘normalized-plastochron index’ (NPI). This concept assigns to a particular stage a fraction of the difference in age of two selected, well-defined, reference stages. The younger reference stage is assigned a value of 0 NP, the older one of 10 NP; stages younger or older are respectively assigned negative values or values greater than 10. The NP- and NPI-concepts permit the construction of a normalized sequence of ontogenesis and, it is hoped, the detection of the temporal patterns of ontogenesis among related species. An example of the application of the scheme of flower development in five species of the Scrophulariaceae is given here.
Submarine pollination of the seagrass Posidoniaaustralis has been studied under controlled conditions. Once released from the anther, the filiform pollen produces precocious pollen tubes when adjacent to the female flower, prior to contacting the stigma. Once in contact with the stigma a bond is formed between the pollen grain and stigma surface coatings. At the site of pollen tube emergence, the pollen grain wall is eroded and the tube wall initiated. Th
e pollen tube penetrates the stigma surface between the receptive cells and a collar of stigma wall material surrounds the tube at this point. Deposition of callose is induced in the stigma cells and stylar transmitting tissue cells adjacent to the pollen tube. A callose plug blocks the tube where it enters the stigma. These features are compared with previous observations made on other hydrophilous angjosperms. The classification of the seagrass stigma is reconsidered and a new form of pollen-stigma interaction proposed.
The development of the pollen grain wall in Xiphidiumcoeruleum (Haemodoraceae) was studied using TEM and cytochemical staining techniques. Microsporocyte ontogeny initiates with the degradation of the cellulosic cell wall and subsequent deposition of a thick callosic cell wall. Following callose deposition, successive meiosis occurs, resulting in a tetragonal tetrad of microspores. during meiosis, the cell walls of the tapetum break down, releasing the sy
ncytial periplasmodium. Irregular non-sporopollenous globular bodies are deposited in this peripheral periplasmodium, which is rich in ER, golgi bodies, vesicles, and characteristic starch plastids. Within the microspore cytoplasm, vesicles, golgi bodies, and plastids are plentiful during the early tetrad stage. At this time the plasma membrane of the microspore develops characteristic evaginations. An extracellular membrane, the ‘white line’, is secreted outside the microspore plasma membrane, followed by callose wall degradation. Bead-like deposits of exine or primexine are deposited at points along the ‘white line’ simultaneously on inner and outer surfaces and opposite the original plasma membrane evaginations. The bead-like exine deposits continue to grow during the release of the microspores and develop into laterally appressed, rod-shaped ektexinous elements having a tangentially oriented commissure, the vestige of the original ‘white line’. The mature intine is two-layered, the outer exintine containing radially oriented vesicular structures, which are apparently derived from plasma membrane extensions. Exine development in Xiphidium is similar to ‘nexine 1’ development in Lilium and may have evolved from an ancestral tectate-columellate condition by the loss of the sexine. Wall development in members of the Zingiberales is strikingly similar to that reported here for the Haemodoraceae—evidence of a possible relationship between the two taxa.
Water deficits at the anthesis stage of rice (Oryza sativa L.) induce a high percentage of spikelet sterility and reduce grain yield. This study attempted to elucidate the direct effects of water stress on panicle exsertion, spikelet opening, and spikelet desiccation leading to spikelet sterility. A well-watered treatment and two water stress levels were imposed in pot-grown plants of IRAT 13 (upland cultivar) and IR20 (lowland cultivar) at the time of flowering under greenhouse conditionsA cult
ivar difference was observed in the flowering response to water stress with a high sensitivity in IR20. The time course of panicle exsertion showed an inhibitory effect due to the low panicle water status. Low panicle water potentials significantly reduced the number of opened spikelets. Spikelet opening was completely inhibited at panicle water potentials below −1·8 MPa and −2·3 MPa in IR20 and IRAT 13, respectively. However, the peak spikelet opening time in a day was not influenced by the stress treatment. Spikelets in stressed panicles were observed to remain open for a longer period than in the well-watered panicles. The role of turgor in spikelet opening is also discussed in the study. At low panicle water potentials, severe desiccation of spikelets and anthers was noted. The deleterious effects of water deficits on spikelet opening and spikelet water loss contributed to reduced spikelet fertility
An efficient method of inducing flowering in the normally strict short-day plant, Xanthium strumarium L., in long days is described. Plants were grown in 16-h long days and subjected to two thermocycles with a root application of gibberellic acid at the 8th h of the light period. A thermocycle was defined as follows. For the first 8 h of the 24-h cycle, the temperature was 4 °C; for the remaining 16 h, it was 23 °C. The light was on for the first 16 h and off for the remaining 8 h.
In Lupinus albifrons flowers the banner spot of the standard is initially coloured white or pale yellow. Two to three days after reaching the stage of full flower opening, this banner spot develops a pinkish blush and is deep magenta after a further 24 h. The development of this pigmentation is accelerated by exposure to ethylene in a concentration- and time-dependent manner. Flowers with a pinkish banner spot produced the greatest amounts of ethylene and production was much lower in flowers whi
ch had either completed the colour change or in which the banner spot colour remained unchanged. Treatments such as stigma removal or pollination increased the rate of ethylene production. Dissection of the flowers showed that while the banner spot is changing colour there is no change in the rate of production of ethylene from the standard, i.e. from the banner spot or surrounding tissue. The major sites of production at this time are the keel and pistil.Isolated flowers withered within 2 d of removal from the plant and therefore did not show any change in the colour of the banner spot unless exposed to ethylene. The increase in banner spot pigment was about fourfold when isolated floweres were exposed to ethylene (0·24 μl 1−1): however, the increase was less than twofold when isolated standards were exposed to ethylene (0·27 μl I−1). Application of silver thiosulphate (STS) to intact isolated flowers, as a 1 h pulse prior to ethylene exposure, partially prevented the pigment accumulation, whilst a continuous supply of STS reduced the ethylene-induced colour change by approx. 50% Low concentrations of cycloheximide (CHI) (0·01 mg ml−1) reduced the accumulation of pigment in the banner spot of ethylene-treated flowers, and higher concentrations (1·0 mg ml−1) completely prevented the ethylene-induced colour change.
Generative cell division in tricellular pollen grains of Sambucus nigra L. (Caprifoliaceae) has been examined with light and electron microscopy. During division the generative cell is located in the centre of the pollen grain, near to the nucleus of a surrounding vegetative cell. Conventional mitosis of the generative cell is followed by cytokinesis through centrifugal cell plate formation. Two sister sperm cells remain in spatial contact with each other and are surrounded, as formerly their pr
ogenitor cell was, by the vegetative cell. From the changes of shape of the generative cell during division and of the sperm cells it may be assumed that the space between these cells and the vegetative one contains a labile, non-rigid, wall material. No plastids have been observed in the generative cell and its mitochondria appear to be unequally distributed between the two future sperm cells during division.
The development of the microspore mother cell walls in Actinidia deliciosa (kiwifruit) has been studied using light and electron microscopy. The microspore mother cell wall is similar, histochemically, and structurally in anthers from both functionally staminate and functionally pistillate flowers. Deposition, which begins during early prophase I, produces an electron-dense multilaminated wall layer (layer a) and by the end of meiosis I a thick electron-lucent layer (layer b) to the inside of th
is multilayered wall. The reasons for histochemical differences and similarities between these layers are discussed. The original primary wall persists until the late uninucleate microspore stage. Layer (b), which is probably mainly callose, dissolves at the late tetrad/early microspore stage while layer (a), which probably also contains other polysaccharides, persists and dissolves concurrently with the primary wall.
Floret elongation and levels of precarthamin were investigated in freshly collected flowers of Carthamus tinctorius. Accumulation of precarthamin was found to be induced at the early stages of floret elongation. [U-14C]Acetate and [U-14C]phenylalanine were incorporated into precarthamin in the detached florets from the flower bud. The results suggest that precarthamin is synthesized via the acetate-shikimate pathway.
Flowering requirements of four Norwegian populations of Phleumalpinum were studied in controlled environments. A dual induction requirement was demonstrated in all populations. Inflorescence initiation had an obligatory requirement for short days (SD) and/or low temperature, while culm elongation and heading were enhanced by long days (LD) and higher temperatures. At 3 and 6 °C primary induction was almost independent of photoperiod, whereas SD was more effect
ive than LD at higher temperatures. The critical temperature for primary induction was about 15 °C in SD and 12 °C in LD. Saturation of induction required 12 weeks of exposure to inductive conditions, although some heading and flowering took place with 6 weeks exposure to optimal conditions (9 °C/SD). Inflorescence development also took place in 8 h SD although it was delayed and culm elongation was strongly inhibited compared with LD conditions. Only small differences in flowering response were found between the populations.
The morphological development of the inflorescence of wild oats and a description of the developmental course of the apex, its branches, spikelets and florets is given. Light and scanning electron micrographs illustrate the sequential stages of development of the inflorescence of wild and cultivated oats which can be divided into three periods. Vegetative development is characterized by the initiation of leaf primordia on the apex. Branch formation is initiated via double ridge-like structures o
n the apex. Branches of 1st, 2nd and higher order are formed and lead to branching of the panicle. Spikelet differentiation starts with the formation of the terminal spikelet on the main axis at right angles to the plane of 1st-order branches. Each branch terminates with a spikelet but the capacity for branching is unlimited. Periods of branch formation and spikelet differentiation overlap each other. Florets are differentiated in an acropetal direction within a spikelet; usually two to three fertile florets are formed, whilst an undifferentiated remainder persists at the tip of the spikelet axis. The stage of development within a panicle decreases both in a basipetal direction from the terminal spikelet and with increasing order of branching. A scale of apical development of oats is proposed, using a decimal code similar to that for the exterior development of cereals. Descriptions and definitions of the various stages in combination with photographs of some important stages are provided.
Floral development in Sonja white clover was examined using scanning electron microscopy. Florets and bracts were found to arise from common primordia initiated as protuberances from the apical meristematic area of the inflorescence. The pattern of floret initiation on the inflorescence was acropetal, the oldest florets resting basally. Floral organ initiation within each floret was acropetal, petals being initiated before stamens. Floret development was zygomorphic, each whorl of floral organs
developing unidirectionally from the abaxial side. There was found to be overlapping in the timing of initiation and development of these organs. Antesepalous stamens were found initially to outgrow their antepetalous counterparts. Early petal development was synpetalous. Eglandular hairs were found basally on the calyx cup and on the pedicel. Procumbent hairs were found to be more numerous and randomly distributed on the abaxial surfaces of the mature calyx cup.
Two principal types of stigma were found in species of Arachis belonging to section Arachis and section Rhizomatosae. The different types did not correlate with sectional classification, genome groups or ploidy level, but did correlate with life form. All the perennial species studied had very small stigmas, which were guarded by a ring of hairs and were difficult to pollinate effectively. Most of the annuals, including the cultivated peanut (A. hypogaea), had larger stigmas, which were not surr
ounded by hairs and which were easily pollinated. One annual species, A. spinaclava, had a stigma intermediate in many of its characteristics between the other two types. Proteins, including esterase and acid phosphatase, were present in all stigmas before the flowers opened. Bud pollination produced apparently normal pollen tube growth in pistils of the wild annual A. spegazzinii and may overcome certain interspecific incompatibilities. Various methods of pollinating stigmas of the perennial species were tried, but even the most successful produced pollen tubes in less than half of the flowers pollinated. Difficulties in pollination, due to stigma morphology, probably explain the limited seed set and poor performance as female parents in interspecific crosses which have been reported for perennial species of Arachis.
The effect of sucrose, H2BO3, KNO3, Ca(NO2)2.4H2O and MgSO4. 7H2O on pollen germination of Phytolacca dodecandra L. (endod) in a liquid medium was investigated. Sucrose and H3BO3 were critical to pollen germination. A concentration of 10% sucrose and 161.8 μm H2BO3 gave over 70% germination. The germination of pollen was not enhanced by Ca(NO3)2.4H2O, KNO3 and MgSO4.7H2O. Endod pollen was dehydrated over CaCl2 and stored in gelatin capsules in cryogenic vials at −175 °C, 1±1 °C and 24±2 °C. The
pollen moisture content at collection was approx. 7.8% (f. wt basis) and dehydration over CaCl2 reduced it to about 1.4%. Pollen stored at 1±1 °C and −175 °C maintained viability for over 6 months. Pollen stored at room temperature lost viability within 4 weeks of storage. Pollination with cryopreserved pollen resulted in normal fruit set.
The floral nectar chemical composition and nectary structure of some Argentinean Bromeliaceae were studied, including field observations on pollinators. Twenty species belonging to eight genera from the three subfamilies were analysed. The nectar components report is mostly new since no comprehensive study has been carried out on the family previously. Sugars were always present, while alkaloids, lipids, phenols, and proteins were not detected in any sample. Reducing acids were found in three sp
ecies. Amino acids were detected in a very low concentration in only about half the samples. Pitcairnioideae species show a mean balanced disaccharide/monosaccharide nectar sugar composition, Bromelioideae had hexose-rich nectars and Tillandsioideae saccharose-dominant ones. Nectar concentration ranged from 16 to 48 %. All taxa bear septal nectaries with many common features. Pitcairnioideae and Tillandsioideae members have half-inferior ovaries, a feature mostly overlooked in previous studies. Three types of nectary architecture were recognized in both subfamilies. Bromelioideae have inferior ovaries and possess comparable nectaries. Hummingbirds constitute the main flower pollinators of many species but butterflies and bees were occasionally seen in two species, cropping nectar and pollen, respectively.
Controlled hand pollinations and field observations were used in conjunction with fluorescence and scanning electron microscopy and fruit and seed set to investigate the timing of stigma receptivity, pollen tube growth and self-incompatibility in relation to fertility in B. coccinea. The species showed both protandry and partial self-incompatibility. Peak stigma receptivity as measured by pollen germination was recorded at 3 d after anthesis and maximum production of stigmatic exudate at 6 d. Po
llen tubes reached the base of the style by 6 d after pollination. A 5 × 5 diallel experiment was conducted and the results measured by pollen tube growth. Self-pollinations generally resulted in poorer tube growth than crosses and there was significant specific and general combining ability as well as reciprocal effects. Cross-pollination resulted in improved fruit set and seed to flower ratio over both selfing and open pollination. Spatial limitations to fertility due to infructescence size were also recorded, but the combination of outcrossing mechanisms and spatial limitation did not entirely account for the low fertility. It is suggested that environmental conditions and the availability of resources may also exert an influence.
The durations of the photoperiod-sensitive and photoperiod-insensitive phases of development to panicle emergence were estimated in four contrasting indica cultivars of rice (Oryza sativa L.) in a reciprocal-transfer experiment. Plants were grown in pots in glasshouses maintained at warmer (32/26 °C) or cooler (28/20 °C) day/night temperatures, and the durations from sowing to panicle emergence were determined for plants moved from relatively short (11 h) to relatively long (13.5 h) days and vic
e versa at various times after sowing. Panicle emergence was delayed by long days in all cultivars, but the traditional cvs Carreon and Peta were much more sensitive to photoperiod than the modern cvs IR8 and IR36 The durations of the photoperiod-insensitive pre-inductive phase (equivalent to some definitions of the basic vegetative phase) varied from 14.4 d in cv. Carreon at 32/26 °C to 42.0 d in cv. IR8 at 28/20 °C. In all cultivars this initial phase was of a longer duration in the cool than in the warm regime. The duration of the photoperiod-insensitive post-inductive phase was also consistently greater, but usually only slight so, at cool than relatively warm temperatures; it varied from 6.8 d in cv. IR8 at 32/26 °C to 272 d in cv. Carreon at 28/20 °C. As expected, the length of the intervening photoperiod-sensitive inductive phase was greater in long days, but the effect of temperature on these durations was not consistent; for example, these durations were longer in warm than in cool temperatures in cv. 1R8 but, if anything, they were slightly longer in cool than in warm temperatures in cv. IR36. This difference is compatible with previous findings that cv. IR36 has a warmer optimum temperature for rate of progress towards panicle emergence than cv. IR8. A subsequent reciprocal-transfer experiment with cv. Peta provided estimates of the durations of the photoperiod-insensitive and photoperiod-sensitive phases of pre-flowering development which were compatible with our earlier estimates. Furthermore, panicle initiation was found to occur after about 80% of the photoperiod-sensitive inductive phase had elapsed. We conclude that although the duration of the photoperiod-insensitive pre-inductive phase in rice is greater than in many other annual crops, genotypic variation in this duration may well be less than was previously deduced. We also conclude that, despite common assumptions to the contrary, photoperiod-sensitivity during rice plant development does not end at panicle initiation.
Ultrastructural changes associated with carnation petal senescence were investigated using ethylene levels of individual petals as a physiological monitor of the senescence process. Limited vacuolar and cytoplasmic vesiculation was observed in pre-senescent petals which became more extensive in pre-climacteric tissues, along with dilation of the outer mitochondrial membrane. Climacteric mesophyll tissue was characterized by widespread cytolysis. Intact cells possessed a highly reduced cytoplasm
and vacuoles with electron-dense deposits. Degenerative changes became evident in the vasculature at this stage. These included occlusion of the sieve plate, and membrane abnormalities in the companion cells. Post-climacteric tissue was characterized by loosening of wall fibrillar structure in the vasculature, the appearance of intracellular cytoplasmic debns and cells completely devoid of contents. These changes are discussed in relation to developmental regulation on the one hand, and increasing levels of membrane disorgamsation on the other, leading to a possible ‘error catastrophe’ and final senescence.
The nectary of Rosmarinus officinalis L. has the form of a four-lobed, asymmetrical disc situated around the base of the ovary. The nectary lobe facing the lower flower lip is enlarged and is the only one to have modified stomata. Vascular strands consisting of phloem only occur in the nectariferous tissue. It is suggested that the pre-nectar originating in the phloem accumulates primarily as starch grains in plastids of the nectariferous cells. The number of grains is very large before anthesis
and decreases considerably at anthesis. The transport of the pre-nectar to the various nectariferous cells appears to be mainly via the symplast. It could not be determined whether the process of elimination of the nectar is solely eccrine or partly granulocrine.
The ultrastructure of the nectary spur of Limodorum abortivum (L) Sw. was examined before and after anthesis. In cross section the nectary spur shows an internal epidermal layer of thin-walled cells bordering the secretory cavity and 10–12 layers of parenchyma cells. The ultrastructure of the secretory cells suggests the involvement of ER, Golgi and plastids in nectar secretion. The nectar accumulated in the sub-cuticular space is released into the nectariferous cavity by rupture of the outer la
In angiosperms, the pollen tube is siphonogamous and its main function is to carry the male gametes for double fertilization. In some taxa, as in Cucurbitaceae, the tube branches after entering the ovule, prior to fertilization. The tube may even swell and form a bulla. During post-fertilization development of the ovule, a portion of the tube may persist in the micropyle, or in the embryo sac, or in both, sometimes even in the micropyle of the mature seed. Haustorial function has been presumed i
n a number of taxa.In Grevillea, following fertilization, the pollen tube branches at the micropyle, and the branches grow intercellularly into the ovarian tissue where further branching occurs. A haustorial role of the pollen tube is presumed from circumstantial evidence. In gymnosperms (for example, Cycas, Zamia and Ginkgo) the pollen tube is nonsiphonogamous, arises from the distal (upper) pole of pollen grain, and grows laterally in the apical region of the nucellus. The tube branches in Cycas and Ginkgo but remains unbranched in Zamia. These pollen tube branches are enucleate, and are not concerned with the transport of male gametes for fertilization. However, the haustorial role has been well documented. In Podocarpus, the pollen tube is siphonogamous and arises from the proximal (lower) pole of pollen grain. After traversing the nucellus, the tube forms a bulla at the point of contact with the female gametophyte, and several branches originate from the bulla. The pollen tube branches grow along the inner surface of the nucellus and the outer surface of the female gametophyte. The haustorial role of the pollen tube branches is uncertain. Procedures for convincingly demonstrating the haustorial role of pollen tubes are discussed.
The breeding systems of an obligate outbreeder (Plantago lanceolata) and an obligate inbreeder (P. patagonica) were compared. Outbreeding in the former and inbreeding in the latter species is achieved by self-incompatibility and preanthesis cleistogamy, respectively. The difference in breeding system is accompanied by a difference in the pollen output, pollen to ovule ratio, stigma and anther size, and seed weight. P. ovata, a third species known only in cultivated form, is intermediate. This sp
ecies has two types of plants, some of which are protogynous and others where stigma receptivity and anther dehiscence synchronize. Although the differences between the two intraspecific variants are not large, they nevertheless suggest that the species is in evolutionary flux. Domestication is known to have modified the breeding system in many crop plants and there is evidence that, in P. ovata, a start in this direction has already been made.
Flower and pod abscission limit soybean yield. A system for quantifying flower and pod development based on the morphological appearance of the flower prior to and following anthesis has been developed to aid in studies of pod abscission. Changes in the appearance of the corolla, primarily the banner petal, are used to distinguish the different stages of the system. External pistil dimensions have been correlated with internal features for each stage of development. From anthesis to pod set, pis
til length and weight increase almost two- and fivefold, respectively, and ovule development progresses from unfertilized egg cells to embryos surrounded by cellular endosperm. Pod determined are correlated with ovule length and width and embryo cell number. Flower and pod stages can be determined in situ, thus permitting non-destructive observation and experimental manipulation of flowers or pods without necessarily impeding their development. Stages have been identified that indicate precisely when pod set occurs and when young pods cease growing and ultimately abscise. This system of flower and pod staging is useful in studies designed to assess effects of abiotic or biotic stress and genetic factors on pod set and abortion.
Durations from sowing to panicle emergence in 16 diverse genotypes of rice (Oryza sativa L.) were recorded in 13 different photothermal regimes, comprising constant and diurnally alternating temperatures between 16 and 32 °C and photoperiods between 10.5 and 15.0 h d−1—all provided by controlled-environment growth cabinets. In 11.5 h days and at sub-optimal temperatures, relations between the rate of progress towards panicle emergence and mean temperature were linear in all genotypes, and amongs
t these the base temperature at that photoperiod varied between 6.6 and 11.9 °C. In most cases progress was most rapid at 24–26 °C, i.e. the optimum temperature was much cooler than expected from previously published values of times to panicle emergence in a less extensive range of photothermal regimes. Only in three cultivars was it warmer than 28 °C, and in these there were sufficient data to establish that relations between rates of progress to panicle emergence and photoperiod in the diurnally alternating temperature regime of 28–20 °C are also linear. Also, the responses of these three cultivars provide no evidence of any interaction between the effects of photoperiod and temperature. We conclude, then, that the model in which rate of development is a linear function of both temperature and photoperiod with no interaction, which has been shown to be common to many other species, also applies to rice. Differences among genotypes in relative sensitivity of rate of progress towards panicle emergence to both temperature and to photoperiod were considerable; japonica cultivars tended to be more sensitive to temperature and less sensitive to photoperiod than indica cultivars. Four indica cultivars bred and selected at The International Rice Research Institute (IRRI) in the Philippines did not differ (P > 0.10) in their relations between rate of progress towards panicle emergence and sub-optimal temperatures in a daylength of 11.5 h, but the optimum temperature for cv. IR 36 was appreciably warmer than that for the cvs IR 5, IR 8 and IR 42.
Pollen grains of Brassica juncea (L) Czern. were exposed to high temperature (45, 60 and 75°C, for 4–24 h) and their viability [using the fluorochromatic reaction (FCR) test], germination, and ability to set fruits and seeds were investigated. High temperature up to 60°C did not affect pollen viability; these pollen samples germinated on the stigma and produced fruits and seeds. There was no correlation between viability and seed set in pollen samples exposed to 75°C; they showed only about 25%
reduction in viability but failed to germinate on the stigma and, consequently, to set seeds. However, these pollen samples induced parthenocarpy. A clear relationship between viability and seed-set was observed when the extent of retention of fluorescence in pollen over a 2-h period was used to assess viability. The fluorescence was retained even after 2 h in pollen samples which induced seed-set, while in those which failed to induce seed-set the fluorescence was lost in about 60 min due to the leakage of fluorescein. Thus, in stressed pollen, the extent of retention of fluorescence may give a better indication of pollen function than initial fluorescence, as is being done routinely in FCR test.
A method was developed for the spatial analysis of plant architecture as it relates to the within-plant variation in the physical, chemical, and postharvest characteristics of the fruit Computer graphics were used to reconstruct the architectural framework and spatial arrangement of the fruit in the canopy of kiwifruit vines (Actinidia deliciosa) trained on two different support structures An infra-red beam theodolite was used to obtain the spatial coordinates of the vines components The data fi
les generated by the theodolite were in turn used with software specifically written for the project (MAPIT—Microcomputer Aided Plant Imaging Technology) to provide a 3-dimensional reconstruction of the original vines Each fruit was colour coded so that extremes in their attributes could be easily identified and accurately located in the canopy of the vine Patterns were clearly discernible for both the pergola and T-bar trained vines The heavier fruit were located at the apical ends of the canes, while greater soluble solids concentrations were associated with the smaller fruit located closer to the cordon These patterns were consistent for all of the vines examined The use of the theodolite coupled with the computer graphics described in this paper provides a rapid and objective means of accurately describing plant architecture
Changes in the freezing tolerance for Silene acaulis L., a subarctic and arctic species of circumpolar distribution, were examined to understand the extent of cold hardening and dehardening that occurs seasonally and with changes in plant phenology. Shoots of whole plants collected on a mountain ridge near Tromsø, Norway (69° N, 700 m above sea level) were frozen under controlled conditions at cooling rates of 3 to 4°C h-1. The extent of freezing-induced injury was examined both by chlorophyll f
luorescence and by visual inspection with a microscope. A freezing tolerance level of -30°C was observed in mid-winter, based on a 50% lethal point for freezing injury. Loss of cold hardiness was substantial in mid-summer, with freezing tolerance of -8·5 to -9°C observed in mid-July. Plants still covered by snow in mid-July had a freezing tolerance of -12·5 to -13°C. The maintenance of a basic level of freezing tolerance throughout the summer may be adaptive in the northern latitude-regions because of the occurrence of episodic frosts during the growing season.
Pollen wall development in Feliciamuricata Thunb. Nees (Asteraceae) was investigated by electron microscopy after addition of the lypophilic dye malachite green to the primary fixative. Pollen wall formation commences with the deposition of fibrillar electron dense units which represent future interbacular spaces. Radially arranged trilammelate structures develop between the fibrillar units. Sporopollenin is deposited in the trilammelate structures. After re
lease of the microspores from the tetrad, formation of interbacular spaces is accompanied by disintegration of fibrillar units. Endexine formation occurs on white lines of unit membrane dimensions. Intine formation follows the pattern described for most angiosperms. Observation of bead-like globules and pollenkitt with a membraneous structure is presumed to be related to the addition of malachite green to the fixative.
tCucurbita pepo carries male and female flowers on the same plant, and is pollinated by nectar-collecting bees. The nectaries are dimorphic in the two sexes and pollen is loaded and unloaded as the bees gain access to the nectar. Both types of flower are open for only 6 h (from 0600 h to 1200 h); male flowers open and close half an hour earlier than female flowers. The latter produce more nectar and are visited more often by the bees than the male flowers. Pollen viability determined by fluoresc
ein diacetate (fluorochromatic reaction) decreases by 20% during anthesis and more rapidly after the flower closes. This decrease is due to dehydration of the grain, especially around the pore where the intine is exposed. An unusual feature of this species is that the grains do not dehydrate before anther dehiscence. Female receptivity has two aspects, that of the stigma lasting 4 d, and that of the ovules lasting 2 d. The receptivity of the two sexes and the short period of anthesis are discussed in the light of the reproductive ecology of the species.
In order to assess the influence of environmental conditions on time of flowering of pea ( Pisum sativum L.), a serial sowing trial was conducted over 2 years at Dijon, France, on two winter cultivars Frisson and Frilene. Time of flowering was analysed according to two variables: the leaf appearance rate RL and the node of first flower NI . RL was linearly related to temperature ( r2 = 0·94). The base temperature was 2°C for both varieties. Growth rate accounted for the residual variability of R
L . Photoperiod and temperature acted on NI in an additive way. Frilene, the later genotype, was more responsive than Frisson. A model for predicting time of flowering based upon these results is proposed. Deviations from this model were related to N nutrition in interaction with the plant water relations. Steps for improving the model are then discussed. Copyright 1993, 1999 Academic Press
The mechanics of the triangular stems of Carex acutiformis was investigated by subjecting sections to bending and torsional tests. The stem was rigid in bending, being stiffened peripherally by lignified material around the vascular bundles, but because of its triangular shape it was vulnerable to local buckling. Despite being and narrow the stem was able to support the seed head, though it sagged appreciably towards the tip. In contrast the stem had very low torsional rigidity, both because of
its triangular shape because the strands of lignified material were isolated from each other. In its lowland habitat this allows the drooping stem to twist away from the light winds, so reducing drag and the chances of self-fertilization. This method of reconfiguring is not possible in the shorter, stiffer mountain sedges which must withstand higher winds; many therefore have more circular stems which will be more efficient at resisting bending. Copyright 1993, 1999 Academic Press
The response of pollen development to low or high temperature regimes was studied to determine the conditions suitable for the formation of fertile pollen in the mango cv. 'Kensington'. The phase most sensitive to the degree and duration of temperature stress was that from meiosis to the pre-vacuolate microspore (about 3 d duration at 25/20 °C) though vacuolated microspores were also sensitive to low temperature. Night temperatures below 10 °C resulted in pollen grains with a low viability (< 50
%). A temperature between 15 and 33 °C during the phase from meiosis to the pre-vacuolate microspore was optimum for pollen development (70-85% pollen viability).
Analysis of field records showed a linear negative correlation between percentage of pollen viability and number of days which had a mean night temperature lower than 10 °C during the period from meiosis to early mature stage (y = 77·7-3·4x, r2 = 0·60). The temperature sensitive phase was estimated to begin 155 degree days D = Σ[(Tmax + Tmin)/2 - 10] before anthesis and to end 78 degree days before anthesis. This equation may be useful as a means of predicting pollen viability in the field from temperature records and thus fruit set, date of maturity and yield. It may also aid in the selection of areas for growing mangoes in marginal climates.
Mercurialis annua L. is a dioecious anemophilous species that (lowers all year round in central and southern Italy. The flowers of both sexes are dimorphic: the female flower has a vestigial calyx; the male flower consists only of a calyx that opens at anthesis. The anthers always dehisce after anthesis. The anihesis of male flowers seems to be temperature dependent, whereas anther dehiscence is related to relative humidity. The pollen grains vary in volume according to the season: they are smal
ler when relative humidity is low and vice versa. They always decrease in volume after anther dehiscence and have the capacity to vary in volume and reach equilibrium with a changing environment. Viability is high, but may drop suddenly during heavy rain or hail that damage the exposed male flowers. The number of pollen grains per stigma varies from 0 to 300. The data is discussed in relation to the type of pollination and environmental characteristics.
In soyabean [Glycine max (L.) Merrill] the period between sowing and flowering is comprised of three successive developmental phases—pre-inductive, inductive and post-inductive—in which the rate of development is affected, respectively, by temperature only, by photoperiod and temperature, and then again by temperature only. A reciprocal-transfer experiment (carried out at a mean temperature of 25 °C) in which cohorts of plants were transferred successively between short and long photoperiods and
vice-versa showed that eight combinations of three pairs of maturity alleles (E1/e1, E2/e2, E3/e3) had their greatest effect on the duration of the inductive phase in long days. This phase was increased with the increasing photoperiod sensitivity induced by the different gene combinations, and ranged from about 27 to 54 d according to genotype. In a short day regime (11-5 h d−1), less than the critical photoperiod, the duration of the inductive phase was brief—requiring about 11 photoperiodic cycles in the less photoperiod-sensitive genotypes and only about seven cycles in the more sensitive ones. The maturity genes also affected the duration of the two photoperiod-insensitive phases; these durations were positively correlated with the photoperiod-sensitivity potential of the gene combinations. The largest effect was on the pre-inductive phase which varied from 3 to 11 d, while the post-inductive phase varied from about 13 to 18 d. As a consequence of these nonphotoperiodic effects of the maturity genes, even in the most inductive regimes (daylengths less than the critical photoperiod) the time taken to flower by the less photoperiod-sensitive combinations of maturity genes was somewhat less than in the more sensitive combinations—ranging from about 28 to 34 d. The genetic and practical implications of these findings are discussed.
All eight isolines of three maturity genes (E1/e1, E2/e2, and E3/e3) of soyabean [Glycine max (L.) Merrill] cv. Clark were grown in widely different combinations of photoperiod and temperature. Under the more inductive conditions, i.e. in a warm mean temperature (30 °C) when daylengths were less than the critical value (i.e. less than about 13 h), the isolines flowered at similar times (23–24 d). The responses of all isolines to temperature were also similar, if not identical. Increase in daylen
gth above the critical photoperiod progressively delayed flowering until the time taken to flower (f) reached a maximum at the ceiling photoperiod. The relations between the rate of progress towards flowering (1/f) and photoperiod (between the critical and ceiling values) were linear. The coefficient characterizing the slope of the response (photoperiod sensitivity) varied amongst the isolines. These responses could be grouped into three categories of increasing sensitivity: (1) least sensitive, e1e2e3, e1E2e3, e1e2E3; (2) intermediate, E1e2e3, e1E2E3, and (3) most sensitive, E1E2e3, E1e2E3, E1E2E3. Thus, in the Clark cultivar genetic background, E1 induces greater photoperiod sensitivity but neither E2 nor E3 on their own have any effect. However, both E2 and E3 together induce photoperiod sensitivity comparable to that induced by E1 alone. Furthermore, in addition to this epistasis, either E2 or E3 has considerable epistatic effect on E1, further increasing photoperiod sensitivity. The effects of these genes and their epistasis were also reflected in the extent of the maximum delays to flowering which occur when the ceiling photoperiod is exceeded, and also possibly in earliness in circumstances when photoperiods were below the critical value.
Nectar is secreted for up to 11d after anthesis in Chamelaucium uncinatum . The volume and sucrose concentration secreted varies between flowers, plants and days. The period of nectar secretion coincides with the period of pollen presentation and stigmatic receptivity suggesting nectar is part of an efficient reproductive strategy in C. uncinatum . The nectary of C. uncinatum consists of the entire upper surface of the ovary and hypanthium. The epidermis of the nectary is covered by a thickened
cuticle which is only broken at the sites of the numerous modified stomata which are scattered across its surface. It is suggested that nectar is secreted onto the surface of the ovary via these modified stomata. The presence of extensive and well developed endoplasmic reticulum, mitochondria and Golgi bodies in the nectar secreting cells indicates that a granulocrine mechanism of secretion is occurring in C. uncinatum .
Morphogenesis of the specialized thread-forming (TF) cells in the Strelitzia reginae anther was investigated; particular attention was given to the cell walls and the degree of vacuolation. The mass of both cell wall and cytoplasm increased until just before dehiscence. However, cell growth and degradation were largely synchronous processes in the TF cells: before any wall thickening could be observed, degradation of primary cell wall material was already initiated. This degradation continued, w
ith the result that the mature thread cells were eventually fully separated from their surrounding cells. Four stages of development, mainly relating to the degree of cell separation, were established. At stage 1, TF cells began to separate from the subepidermis, while at stage 2 some initial cell wall thickening was taking place. The walls of the TF cell were, at stage 3, thickened considerably (about 1 μm), especially along the radial axes. The texture of these walls was loose due to the presence of large intermicrofibrillar regions, and the previously vacuolated cells were filled with cytoplasm. Longitudinal sections revealed conical gaps in the thick cell wall over the plasmodesmata. Just before dehiscence (late stage 3), the TF cells separated from each other and the subepidermis to such an extent that only plasmodesmata and fibrillar wall remnants kept the files of TF cells in place. The released uniseriate threads were classified as stage 4. (Occasionally the threads were multicellular but only where the transverse walls had not separated from each other.) The threads had thinner cell walls than the TF cells at stage 3 and were vacuolated.
The environmental control of flowering in some arctic-alpine Carex species has been studied in controlled environments. Carex nigra, C. brunnescens, C. atrata, C. norwegica and C. serotina all had a dual induction requirement for flowering. In all except C. nigra either low temperature (12 °C or lower) or short days (SD) over a wider range of temperatures were needed for primary floral induction and inflorescence formation. In C. nigra primary floral induction took place in SD only (9–21 °C), 8–
10 weeks of exposure being required for a full response. In all these species long days (LD) were required for, or strongly promoted, culm elongation and inflorescence development (secondary induction). Quantitative ecotype differences in both primary and secondary induction were demonstrated. Unlike the other species, C. bicolor proved to be a regular LD plant which required LD only for inflorescence initiation and development. In all species leaf growth was strongly promoted by LD, especially in the higher temperature range (15–21 °C). In SD and temperatures below 15 °C the leaves became senescent and the plants entered a semi-dormant condition which was immediately reversed by LD. The results are discussed in relation to growth form and life history of shoots.
This report deals with the male reproductive component of Butomus umbellatus and examines pollen development, presentation, viability and germinability, as well as pollen tube growth and penetration into the micropyle. Our developmental assessment presents a comprehensive description of the male reproductive processes in B. umbellatus , describes a variety of developmental irregularities starting with meiosis, and discriminates pre- and post-pollination developmental factors causing reduced male
reproductive potential. Developmental irregularities that occur in B. umbellatus include meiotic aberrations, pollen abortion, differences in pollen tube diameter, variations in sizes and frequency of callose plugs, excessive winding of pollen tubes and pollen tube branching. These are apparent under in vitro , glasshouse and field conditions, suggesting that such irregularities are innate and unlikely to be due to environmental or nutritional constraints. The lack of difference between self- and cross-pollinations indicates that the developmental peculiarities observed are not due to self-incompatibility reactions. The low numbers of viable pollen grains or grains with a normal appearance are attributed to meiotic aberrations that most likely affected successful division of uninucleate into binucleate pollen grains and subsequent pollen tube growth patterns. In spite of the differences in pollen tube growth patterns, inconsistent pollen tube penetration and pollen tube branching, many of these tubes end up in the micropyle. Therefore, reduced male reproductive potential in B. umbellatus is largely due to pre-pollination developmental events.
Plantain-derived tetraploid hybrids are routinely crossed inMusabreeding programmes with diploidMusaaccessions for the efficient generation of putative triploid hybrid seed. However, natural open pollination of these same tetraploid hybrids also consistently generates viable seed. The mean germination rate of such open pollinated seed was observed to be higher than that of seed generated from artificial pollinations. This may suggest that tetraploidMusahybrids played a much more important role i
n the evolution of triploidMusalandraces than previously considered. Moreover, the elite performance of certain hybrids generated through such open pollination offers possibilities of newMusabreeding paradigms. The inferences of these observations forMusaevolution and the implications forMusabreeding are discussed.
Pollen released at 1100 h has the highest viability (92.2%) but is no longer viable 3 d (84 h) after anthesis. In vitro pollen-tube growth is fast (140 μm h −1 ) and increases significantly within the first 8 h. In vivo pollen tubes also grow quickly and reach the base of the style within 2 h after pollination and enter the micropyle 8 h after pollination. There is no significant difference between self- and cross-pollination in either the rate and the number of pollen tubes in the pistil and th
e number of ovules penetrated by a pollen tube. Teak has late-acting gametophytic self-incompatibility; the majority of pollen tubes grow through the style but some do not continue to grow from the style towards the embryo sacs. Pollen-tube abnormalities include swollen, reversed, forked and tapered tips and irregular and spiralling tubes. These are most prevalent in self-pollination (20.4%). The index of self-incompatibility of 0.17 and low fruit set following self-pollination (2.49%) indicates that teak is mostly self-incompatible. Drastic fruit abortion occurs within the first week following controlled pollination. Within 14 d, fruit size and fruit set from cross-pollination is generally much greater than from self-pollination.
Flowering plants often produce ovules that do not develop into seeds. Lack of pollination, insufficient resources, environmental constraints and incompatibility reactions are often considered to be causal factors. Pre-pollination and post-fertilization developmental irregularities (DI) are less commonly implicated as causal factors, usually because information on them is limited. The results of a detailed developmental assessment of sexual reproduction in B. umbellatus using self- and cross-poll
inated glasshouse and open-pollinated field-grown plants, reveal a high degree of pre-pollination and post-fertilization DI. Pre-pollination DI account for a large fraction of the species' low reproductive potential. Post-fertilization DI represent another crucial reduction in the species' reproductive output. Seed set in B. umbellatus is less than 1%. In the female reproductive component, these DI include embryo sacs with hypertrophied or highly vacuolate eggs, collapsed synergids, collapsed egg apparati and embryo sacs that are empty, uninucleate or with disorganized mass of nuclei; there are also ovules with no embryo sacs. Post-fertilization DI include zygotes that are hypertrophied, highly vacuolate and collapsed, and malformed embryos. The lack of an obvious adaptive significance to the array of DI in B. umbellatus suggests that these are unlikely to be due to self-incompatibility reactions, and physiological or environmental constraints. Since B. umbellatus is a long-lived species, it is highly possible that disadvantageous mutations have accumulated in its clonal lineages causing a considerable load in terms of faulty meiosis resulting in defective meiotic products, a series of DI, and therefore, limited sexual reproduction.
The influence of temperature and photoperiod on phenological development of three bambara groundnut (Vigna subterranea) selections from Botswana, Zimbabwe and Mali was investigated in a semi-controlled environment experiment with factorial combinations of three constant temperatures (20.9, 23.4 and 26.2 °C) and four constant photoperiods (10.0, 12.5, 13.5 and 16.0 h d−1). In all three selections, the onset of flowering was influenced by temperature but not by photoperiod, while the onset of pod-
growth (‘podding’) of all three selections was influenced by both factors. The influence of temperature and photoperiod was quantified by means of photothermal models, linking development rates to temperature and photoperiod with linear equations. The rate of progress from sowing to flowering of the three selections could be described very well (r2>95%) as a function of temperature; the rate of progress from flowering to podding was described reasonably well as a function of both temperature and photoperiod by a combination of one to three response planes (r2for the different selections ranging from 63 to 90%). Model testing with independent data sets showed good agreement between observed and predicted times to flowering and podding.
Gibberellic acid (GA 3 ) promotes parthenocarpic fruit development and is used commercially to increase fruit set in many crops. However, fruit size is usually smaller than that of pollinated fruit. The purpose of this work was to determine the anatomical basis for differences in fruit size between pollinated and GA 3 -induced parthenocarpic blueberry ( Vaccinium ashei Reade) fruits. Fresh weights at ripening averaged 1.6 and 2.5 g for GA 3 -treated vs . pollinated fruits, respectively. In both
pollinated and GA 3 -treated fruits, mesocarp cell number comprised about 75% of the total pericarp cell number, and increased from ∼7000 cells per cross-sectional area at bloom to ∼9000 at harvest. The duration of the cell division period in pollinated and GA 3 -treated fruits was similar, with the majority of cell division ceasing by 24 d after bloom (DAB). Cell size in both middle and inner mesocarp of ripe pollinated fruits was significantly larger than in ripe GA 3 -treated fruits (31000 vs . 22000 μm 2 ). Differences in final fruit size between pollinated and GA 3 -induced parthenocarpic blueberry fruit are due to differences in cell enlargement rather than cell number.
The effects of temperature, photoperiod and light integral on the time to first flowering of pansy ( Viola×wittrockiana Gams) were investigated. Plants were grown at six temperatures (means between 14.8 and 26.1 °C), combined with four photoperiods (8, 11, 14 and 17 h). The rate of progress to flowering increased linearly with temperature (up to an optimum of 21.7 °C) and with increase in photoperiod ( r2 =0.91, 19 d.f.), the latter indicating that pansies are quantitative long day plants (LDPs)
. In a second experiment, plants were sown on five dates between July and December 1992 and grown in glasshouse compartments under natural day lengths at six temperatures (means between 9.4 and 26.3 °C). The optimum temperature for time to flowering decreased linearly (from 21.3 °C) with declining light integral from 3.4 MJ m −2 d −1 (total solar radiation). Data from both experiments were used to construct a photo-thermal model of flowering in pansy. This assumed that the rate of progress to flowering increased as an additive linear function of light integral, temperature and photoperiod. Independent data from plants sown on three dates, and grown at five temperatures (means between 9.8 and 23.6 °C) were used to validate this model which gave a good fit to the data ( r2 =0.88, 15 d.f.). Possible confounding of the effects of photoperiod and light integral are discussed.
Effects of nitrogen (N) supply on leaf and flower development in Lupinus angustifolius L. cv Merrit were examined in a temperature-controlled glasshouse. Low N supply (0.05 or 0.4 m M N) had little effect on leaf initiation but slowed leaf emergence on the main stem compared with plants receiving high N supply (6.0 or 6.4 m M N), or with symbiotic N 2 -fixation. Plants experiencing transient N deficiency had slower leaf emergence than plants with a continuous supply of 6.4 m M N. Nitrogen supply
did not affect the time of floral initiation, which occurred within 4 weeks of sowing, by which time nine to ten leaves had emerged. However, the flowering of low-N plants was delayed by 68 to 220 °C d (i.e. 4–14 d) even though they had fewer leaves. The effect of N deficiency on flowering time was largely a result of slower leaf emergence.
To examine flower opening and closing of a Portulaca hybrid, flower buds were placed in darkness for 12 h (2030–0830 h) at 20 °C and then exposed to various light-temperature conditions. Flower buds exposed to light at 25, 30 or 35 °C opened within 1 h, and wilted 10–14 h later. Flower buds exposed to light at 20 °C started to open after 4 h but opened slowly and not completely. Flower buds subjected to 25, 30 or 35 °C in darkness also opened rapidly, but did not reach full opening. Flowers open
ed at 30 °C in light, and partially closed and opened repeatedly in response to cycles of a 2-h exposure to 20 °C and a 2-h exposure to 30 °C at any time between 1000 to 1600 h. Similar phenomena were observed when the flowers opened at 30 °C in light and then were subjected to darkness and light alternately at 30 °C, although the effect of light was less obvious than that of alternating temperature. Flower opening and closing were not affected by relative humidity. These results indicate that a rise in temperature is required for rapid flower opening in the buds kept at 20 °C, and that light intensifies the effect of high temperature. Exposure to light without a temperature change delayed and slowed flower opening which was never complete. The involvement of an endogenous rhythm in flower opening by Portulaca is indicated.
Floral biology and pollination mechanism of the Acacia hybrid ( A. mangium Willd. × A. auriculiformis A. Cunn. ex Benth.) growing in Thailand are investigated using light and electron microscopy. The hybrid is andromonoecious. A floral spike consists of about 150 loosely arranged flowers. Flowers are cream coloured, fragrant and have no floral nectaries. The pistil has a solid style with a smooth, wet stigma and amphitropous ovules with immature integuments. The anther consists of eight loculi,
each bearing only one 16-grain polyad. The flowers are weakly protogynous. Anthesis is complete at 0500–0600 h but peak female receptivity begins at 0200–0300 h and is completed that day. The stigmatic exudate is of the lipophilic type and is secreted from the stigmatic cells by a holocrine mechanism. Pollen is the main floral reward for the insect pollinators. There are several floral characteristics which facilitate pollen transfer from anthers and deposition on stigmas. Apis mellifera and Ceratina sp. are the most effective pollinators because they are the most common visitors and carry a heavy load of hybrid polyads. However, their behaviour in foraging for pollen in the same tree and weak protogynous dichogamy may promote self-pollination in the hybrid. The hybrid has low pollination success due to low pollinator number. An increase in exposure time of flowers to pollinators or pollinator number may increase pollination success but may not affect the rate of pollen deposition on stigmas due to the relatively small size of the stigma in relation to the polyad.
Exposure to high temperature (30 °C) before or after exposure to low temperature (0, 4 or 8 weeks at 4 °C) consistently increased the number of leaf nodes at flowering and delayed flowering in a range of genotypes of spring rape (Brassica napus var. annua L.). Four days of prior exposure to high temperature had more effect than 2 d, and the effect of subsequent exposure to high temperature was maximized when exposure commenced 1 week after the end of the low-temperature treatment. In genotypes t
hat showed a vernalization response (i.e. in which the number of leaf nodes at flowering was reduced or flowering was advanced by low temperature), this response was reduced or eliminated by either prior high-temperature treatment (antivernalization) or subsequent high-temperature treatment (devernalization). A biochemical model to account for these effects is proposed.
The combined forces of developmental biologists, studying primordium initiation at the stem apex, and mathematical modellers, developing simulations of crop growth and development, have brought about considerable advances in the understanding of the control of flowering in wheat and barley. Nevertheless, there are still major gaps in this understanding including: what determines the basic rate of development (magnitude of the phyllochron or plastochron); how temperature and photoperiod interact
to bring about the transition from vegetative to reproductive development; and how flowering occurs eventually in the absence of inductive conditions. Although geneticists have tended to measure cereal flowering in terms of ‘days from sowing or emergence to heading’, results of studies using aneuploids and molecular markers are compatible with the roles for photoperiod and low-temperature vernalization established in purely-physiological or developmental investigations. They have also revealed the existence of ‘earliness per se ’loci, whose detailed roles have yet to be established. Progress towards isolating and characterizing wheat and barley loci is hampered by the poor resolution of mapping (location to a precision of tens of thousands of base pairs). Neither of these broad approaches promises a rapid resolution of the factors controlling the induction of flowering. Two expanding areas of molecular genetics now provide potential for greater understanding of cereal flowering. First, the extensive homoeology among members of the Gramineae can be employed to establish the existence and location of genes or quantitative trait loci in rice which correspond to controlling loci in wheat or barley. Since the rice genome is 1/30th of the size of the wheat genome, the accuracy of mapping loci can be much higher, and there is greater potential for precise location of loci using techniques such as chromosome walking. With the ultimate cloning of individual genes, and the isolation of gene products, the relative roles of the 20 loci apparently involved in the induction of flowering of wheat could be explored. However, progress in the molecular genetics of Arabidopsis (the second area) may provide a more rapid route to understanding the control of flowering in cereals for several reasons: its small genome (1/4 that of rice); the likelihood of extensive homoeology with cereals, in spite of differences in codon usage between monocots and dicots; the existence of a wide range of flowering-time mutants; and the control of floral induction by a similar range of environmental factors including photoperiod and low temperature. It is likely that the MCDK (Martinez-Zapater, Coupland, Dean and Koornneef, 1994. In: Meyerowitz EM, Somerville CR. Arabidopsis. New York: Cold Spring Harbor Laboratory, 403–433) model, formulated to explain the genetic and environmental control of flowering in Arabidopsis, could be employed usefully in the formulation of experimental work on flowering in wheat and barley. This paper reviews these issues, paying particular attention to the significance of ‘earliness per se ’ loci and the ‘constitutive floral pathway’ for wheat and barley.
Primula vulgaris Huds., P. veris L., P. frondosa Janka, and three populations of P. farinosa L. were legitimately and illegitimately pollinated, and the self-fertile P. scotica selfed and cross-pollinated and then subjected to uniform temperature conditions of 6, 15 or 26 °C for 4 d before gynoecia were examined for pollen germination and pollen tube growth, or plants progressed to seed set at 15 °C, after which seeds were weighed, germinated, and seedlings grown on. The temperature responses of
pollen germination and pollen tube growth were not always congruent, and varied between species, populations, and often between morphs (pin and thrum) in the distylous species. Nevertheless, optimal temperature responses tended to be lower for vernal species ( P. vulgaris and P. veris ) and for subarctic P. scotica than for later flowering montane species. However, no relationship was found between pollen temperature response, and fertility. The greatest seed set occurred after legitimate pollination at 15 °C in most cases; a flowering temperature of 26 °C tended to impede seed set, except for P. scotica and the low altitude population of P. farinosa . In P. veris, P. frondosa and the high altitude population of P. farinosa, some illegitimate pollen germination and pollen tube growth occurred at 26 °C, but this did not lead to increased within-morph seed set in these self-incompatible species at this relatively high temperature. Temperature at flowering frequently affected average seed weight, and in P. veris and two populations of P. farinosa this attribute may have been influenced by seed number, the average seed weight of few-seeded capsules tending to be greater than for many-seeded capsules. A high seed weight might mitigate the disadvantageous effects of low fecundity resulting from interactions with flowering temperature. However, in P. vulgaris and P. scotica interactions between flowering temperature and seed weight may have other, undetermined, causes. The seed of four species germinated least well in standard conditions when set following a flowering temperature of 6 °C, which tends to support the hypothesis that temperature at flowering can affect seed physiology; in contrast the seed of the two upland populations of P. farinosa germinated least well after flowering at 26 °C. We conclude that much more work is needed on interactions between temperature and reproductive efficiency, but that preliminary indications suggest that a global increase in temperature at flowering might adversely affect the quantity and quality of seed set in some species.
Observations were made on Dendrocalamus giganteus clumps in six locations in the Kandy district of Sri Lanka when 23 out of 111 clumps flowered from 1990 to 1996. Examination of fresh florets confirmed their description by Munro in 1868 (Clayton et al ., 1994. In: Dassanayake MD, Fosberg FR, Clayton WD, eds. A revised handbook of the flora of Ceylon.Vol. VIII . New Delhi: Amerind Publishing, 1–458). Flowering behaviour was similar to that reported by Macmillan (1907, Annals of the Royal Botanic
Gardens, Peradeniya. Vol IV : 123–129) when the species first flowered after its introduction to Sri Lanka. Giant inflorescences bearing numerous florets developed in flowering clumps. Seed set was rare. Except for two clumps that died, the others survived after flowering. Precocious flowering was seen in a 4-year old seed-raised plant. Vegetative growth was related to the seasonal rainfall, while flowering did not appear to be related to any external factor; but the development of vegetative shoots from floral primordia of in vitro cultured inflorescences indicated the possible reversal or deviation of flowering by external factors. Flowering behaviour did not indicate mast seeding, while the relatively large proportion of clumps that flowered ruled out sporadic flowering. It was not possible to confirm that the species had a flowering cycle of 76 years as reported by Janzen (1976, Annual Review of Ecology and Systematics7 : 347–391). It was more likely to be a population of cohorts with different flowering cycles. Copyright 1998 Annals of Botany Company.
This paper presents a plant phenological model based on genotype×temperature×photoperiod interaction (GPTmodel). In the model, rate of development towards a specified stage (e.g. flowering) for a given genotype is composed of three components: the genotype's maximum rate of development; any delay due to a non-optimal temperature; and any delay due to a photoperiod response. It is assumed that development to the specified stage is an autonomous process established by most, if not all, genes other
than the vernalization genes and the photoperiod genes; and that this autonomous process is delayed by any activity of the photoperiod genes. Since all physiological processes are modulated by temperature, any photoperiod response is inevitably a photoperiod×temperature interaction. This interaction is simulated by assuming that the photoperiod gene activity occurs only beyond a critical photoperiod (Pc) and is enlarged by temperature above a base temperature (Tbp) that allows the photoperiod gene activity. The model is written as R=1/Db − St (T−Topt) 2 − Sp (T−Tbp) ∣ P−Pc ∣, where R is the expected rate of development to the specified stage under any combination of temperature (T) and photoperiod (P). The other model parameters are: Sp , the sensitivity to a delaying photoperiod; Topt , the optimum temperature for development in the absence of the photoperiod response; St , the sensitivity to a non-optimum temperature; and Db , the basic duration to the specified stage (or intrinsic earliness), the inverse of which is the maximum rate of development. Db is observable only if T=Topt and simultaneously P ⩾ Pc for long-day plants (LDP) but P ⩽ Pc for short-day plants (SDP). The model is shown to successfully simulate and predict the published phenological data of five crops, viz. long-day plants: pea (Pisum sativum L.), oat (Avena sativa L.), and wheat (Triticum aestivum L.), and short-day plants: bean (Phaseolus vulgaris L.) and maize (Zea mays L.).
Exogenous gibberellin A 3 (GA 3 ) reduced the number of leaf nodes at flowering and time to flowering and increased the stem height at flowering in three genotypes of spring rape ( Brassica napus var. annua L.). The responses to GA 3 were similar to those for long days (LD) and low-temperature treatments, suggesting that the effect of photoperiod and the vernalization response are probably mediated through gibberellins. The response to exogenous GA 3 was greatest in non-cold-treated plants in sh
ort days (SD) suggesting that endogenous GAs are limiting in these conditions. CCC, an inhibitor of gibberellin biosynthesis, caused a small increase in the number of leaf nodes at flowering and time to flowering and a small decrease in the stem height at flowering, but unexpectedly, its effect was hardly influenced by the application of exogenous GA 3 . Genotypes that showed the clearest responses to the treatments with regard to the number of leaf nodes at flowering and time to flowering did not show the clearest responses with regard to the stem height at flowering; the pattern of responses of the number of leaf nodes at flowering and time to flowering was distinct from that of stem height at flowering. This indicates that flower formation and stem elongation are separable developmental processes which may be controlled by different endogenous gibberellins, different levels of a specific endogenous gibberellin, or different responses to gibberellin.
Flower and immature fruit abscission can be caused by proximate factors preventing the development of all flowers into mature fruits. Two potential limiting factors, pollen supply and carbohydrate availability, were assessed as relative constraints on accumulation of fruit dry matter in Persoonia rigida (Proteaceae). Natural pollen transfer was highly efficient, and no evidence of self-incompatibility was found. Levels of fruit set (67.4% following open-pollination and 50.4–58.8% following hand-
pollinations) may be the highest recorded for a species of Proteaceae with hermaphroditic flowers. Fruit abscission occurred principally in a single phase from 4–10 weeks post-anthesis, with a peak during the eighth week post-anthesis, and this early abscission was the result of fertilization failure in some flowers. Manipulation of carbohydrate availability by girdling and/or defoliation of branches provided evidence that carbohydrate supply affected fruit set only when supply was very low. Fruit abscission due to very low carbohydrate availability on defoliated branches was evident during the early abscission phase but was more pronounced during the second half of the fruit development period (>17 weeks post-anthesis), coinciding with the period of greatest dry matter demand by the fruits. Minimal fruit abscission occurred during this later period on leaf-bearing branches. Increases in carbohydrate supply had no effect on fruit set, but fruit size was highly sensitive to carbohydrate availability. Subtending and adjacent leaves were identified as major contributors to the carbohydrate supply of fruits, although some carbohydrate could be obtained from beyond the fruiting branch. Despite the high levels of natural fruit set, both pollen supply and resource availability were indicated as potential constraints on accumulation of fruit dry matter in P. rigida.
Hot days and warm nights are important environmental factors limiting fruit yields of groundnuts in the semi-arid tropics. The objective of the present research was to quantify the effects of short episodes of heat stress on pollen production and viability, and fruit yield. Plants of cultivar ‘ICGV 86015’ were grown at a day/night temperature of 28/22 °C from sowing until 9 d after flowering. Cohorts of plants were then exposed to a factorial combination of four day (28, 34, 42 and 48 °C) and tw
o night (22 and 28 °C) temperatures for 6 d. Thereafter, all plants were maintained at 28/22 °C until final harvest 9 d later. Number of flowers per plant (FN), the proportion of flowers setting pegs (fruit-set), the number of pegs and pods per plant (reproductive number, RN t ), pollen production per flower and pollen viability were determined during the 6 d stress period. There were strong negative linear relations between day temperature over the range of 28 to 48 °C and FN (slope, −1.1 °C −1 ), fruit-set (−2.8% °C −1 ), RN t (−0.90 °C −1 ), and pollen production (−390 °C −1 ) and viability (−1.9% °C −1 ). Warmer night temperature (28 vs. 22 °C) had no effect on FN, but reduced fruit-set (31 to 19%), RN t (8 to 5), and pollen production (4389 to 2800) and viability (49 to 40%). There were no significant interactions between day and night temperature. Reduced fruit-set was a consequence of fewer pollen grains and reduced pollen viability. The threshold day temperature for pollen production and viability was 34 °C and there were strong negative linear relations between both pollen production and pollen viability and accumulated temperature >34 °C.
Treatments consisting of maceration of the centre of the shoot apical meristem or localized application of the plant hormone, indoleacetic acid (IAA), to apical flower buds or the estimated centre of the shoot apex were made to test their effect, if any, on flower shape or symmetry. Both types of treatment affected flower symmetry. IAA treatment was most successful, but it also affected the completeness of the flower, producing a small number of reduced flowers. Alteration of symmetry was, howev
We studied the morphology of the androecium in 168 species and subspecies of Fabaceae from SW Europe and its relationship with nectar production. Six androecium types were recognized: monadelphous; pseudomonadelphous without basal fenestration; pseudomonadelphous with basal fenestration; diadelphous; reduced diadelphous; and androecium with free stamens. The monadelphous androecium appears in the tribe Genisteae, in Ononis , and in Galega officinalis, and the pseudomonadelphous without basal fen
estration only in the genus Coronilla, with both types having the same functionality—they are linked to the absence of nectar from an intrastaminal nectary, their taxa being mostly polliniferous. The pseudomonadelphous androecium with basal fenestration appears in around 38% of the taxa studied and has the same functionality as the diadelphous androecium: there is nectar secretion from an intrastaminal nectary in both. The reduced diadelphous androecium only appears in three species ( Biserrula pelecinus, Vicia pubescens and Astragalus epiglottis ), and its functionality could be related to the syndrome accompanying autogamy in Angiosperms. The free stamen androecium may imply a greater nectar production than other types.
Twenty-four plant species native or naturalized in Britain were grown in the Cambridge University Botanic Garden, UK and evaluated as potential resources for nectar-foraging bees, butterflies and hoverflies. In ten plant species a series of measurements were made, at regular intervals from dawn to dusk, of nectar secretion rate and standing crop, and in all species insect visits were monitored throughout daylight hours. The study revealed differences between plant species in the composition of t
he assemblage of insect visitors, and in the magnitude and temporal distribution of the nectar reward. In some cases we found interesting correlations between temperature and secretion rates or patterns of insect visits. Species that received numerous insect visits in our study are potentially valuable forage plants that might be planted by gardeners to support local pollinator populations. Deep flowers whose nectar is accessible to long-tongued bumblebees ( Bombus hortorum, B. pascuorum ) but not to honeybees may provide long-tongued pollinators with a resource refuge relatively free from honeybee competition. Features that make some of those plant species particularly interesting to observe in the garden include robbing by short-tongued bumblebees in Saponaria, baseworking by honeybees on closed flowers in Malva sylvestris , and apparent displacement of bumblebees by territorial behaviour of the solitary bee Anthidium manicatum on species of Stachys.
We investigated whether partial self-sterility in Calluna vulgaris results from abortion of selfed offspring owing to inbreeding depression or a late-acting self-incompatibility mechanism, and whether self-pollen interferes with normal functioning of cross-pollen. Self-pollination resulted in 75% less seed set than cross-pollination. Self-pollen tubes reached ovaries and penetrated ovules as often as those of cross-pollen. Following self-pollination, examination of the size of undeveloped seeds
showed that at least 70% resulted from ovule fertilization and arrest of development occurred at various stages. All self-pollinated plants produced seeds and self-fertility varied among plants. These results indicate that the reduced seed set observed in self-pollination is more likely the result of inbreeding depression rather than a late-acting self-incompatibility system. The fecundity component of inbreeding depression was high (0.762). Seed set was reduced by an average of 40% when self-pollen was mixed with cross-pollen, compared to pure cross-pollination. Using genetic markers, we found about 20% of seeds resulted from self-pollination in mixed-pollinated fruits. C. vulgaris is likely to experience self-pollination in nature and our data suggest this will reduce the number of ovules that might otherwise mature after cross-pollination.
A comparison between bat-pollinated plant assemblages at two sites in different altitudinal ranges covered by the Atlantic rainforest in southeastern Brazil is presented. The lowlands (5–90 m) harbour ten plant species in seven families, pollinated mostly by three glossophagine bat species. The highlands (1540–1600 m) harbour seven plant species in five families, pollinated by a single species of glossophagine. Bromeliads account for about 30% of the bat-pollinated species at each assemblage. Tu
be and brush shapes prevail in the flowers at both sites. Corolla lengths averaged 26.8 and 37.2 mm, sugar concentrations in nectar averaged 15.0 and 18.1%, and nectar volumes averaged 150.8 and 167.0 μl in the lowland and highland assemblages, respectively. The flowers are pollinated mostly by glossophagine bats during hovering visits, and the plants are visited in the trap-line foraging pattern. The plants bloom annually and both assemblages show a staggered continual flowering pattern. Flowering seasonality was found at both sites, with flowering clustering in the drier season at the lowland site and in the wetter season at the highland site. The ratio between bat-pollinated and hummingbird-pollinated species is 0.24 at the lowland site and 0.23 at the highland one. These similar values indicate that additional studies on bat- and bird-pollinated assemblages are merited at other Atlantic rainforest sites.
Garden flowers can be valuable to wildlife if they produce nectar, pollen and/or seeds. To provide information needed by gardeners to select wildlife-friendly plants, we investigated nectar production and insect visits to Tropaeolum majus, Consolida sp., Antirrhinum majus, Viola×wittrockiana, Tagetes patula and Alcea rosea , in each case comparing a near-original flower type with a cultivar that had spurless, doubled, peloric or enlarged flowers. All species showed high secretion rates and stand
ing crops of nectar. In most cases the horticultural modifications affected the numbers or species composition of the assemblage of insect visitors, and they generally reduced the value of the floral reward to insects, often affecting accessibility. Effects on seed yield were not investigated directly here, but are likely to further reduce the wildlife value of modified variants.