Photoperiod-induced changes in gibberellin metabolism in relation to apical growth and senescence in genetic lines of peas (Pisum sativum L.)

In an early-flowering line of pea (G2) apical senescence occurs only in long days (LD), while growth in short days (SD) is indeterminate. In SD, G2 plants are known to produce a graft-transmissible substance which delays apical senescence in related lines that are photoperiod-insensitive with regard to apical senescence. Gibberellic acid (GA₃) applied to the apical bud of G2 plants in LD delayed apical senescence indefinitely, while N⁶-benzyladenine and -naphthaleneacetic acid were ineffective. Of the gibberellins native to pea, GA₉ had no effect whereas GA₂₀ had a moderate senescence-delaying effect. [³H]GA₉ metabolism in intact leaves of G2 plants was inhibited by LD and was restored by placing the plants back in SD. Leaves of photoperiod-insensitive lines (I-types) metabolized GA₉ readily regardless of photoperiod, but the metabolites differed qualitatively from those in G2 leaves. A polar GA₉ metabolite, GA_E, was found only in G2 plants in SD. The level of GA-like substances in methanol extracts from G2 plants dropped about 10-fold after the plants were moved from SD to LD; it was restored by transferring the plants back to SD. A polar zone of these GA-like materials co-chromatographed with GA_E. It is suggested that a polar gibberellin is synthesized by G2 plants in SD; this gibberellin promotes shoot growth and meristematic activity in the shoot apex, preventing senescence.Abbreviations GA gibberellin - GA₃ gibberellic acid - SD short days - LD long days     

The Control of Apical Bud Growth and Senescence by Auxin and Gibberellin in Genetic Lines of Peas

Pea (Pisum sativum L.) lines G2 (dwarf) and NGB1769 (tall) (Sn Hr) produce flowers and fruit under long (LD) or short (SD) days, but senesce only under LD. Endogenous gibberellin (GA) levels were inversely correlated with photoperiod (over 9-18 h) and senescence: GA20 was 3-fold and GA1 was 10- to 11-fold higher in flowering SD G2 shoots, and the vegetative tissues within the SD apical bud contained 4-fold higher levels of GA20, as compared with the LD tissues. Prefloral G2 plants under both photoperiods had GA1 and GA20 levels similar to the flowering plants under LD. Levels of indole-3-acetic acid (IAA) were similar in G2 shoots in LD or SD; SD apical bud vegetative tissues had a slightly higher IAA content. Young floral buds from LD plants had twice as much IAA as under SD. In NGB1769 shoots GA1 decreased after flower initiation only under LD, which correlated with the decreased growth potential. We suggest that the higher GA1 content of G2 and NGB1769 plants under SD conditions is responsible for the extended vegetative growth and continued meristematic activity in the shoot apex. This and the increased IAA level of LD floral buds may play a role in the regulation of nutrient partitioning, since more photosynthate partitions of reproductive tissue under LD conditions, and the rate of reproductive development in LD peas is faster than under SD.     

Photoperiodic and genetic control of carbon partitioning in peas and its relationship to apical senescence

Apical senescence but not flower initiation is delayed by short days (SD) compared to long days (LD) in pea plants (Pisum sativum L.) of genotype E Sn Hr. We recently reported that delay of senescence correlated with slower reproductive development, suggesting that fruits are weaker sinks for assimilates under delayed senescence conditions. Thus, we have examined assimilate partitioning in peas to determine if genotype and photoperiod regulate relative sink strength. Assimilate diversion by developing fruit has been implicated in senescence induction. A greater percentage of leaf-exported ¹⁴C was transported to fruits and a smaller percentage to the apical bud of G2 peas (genotype E Sn Hr) in LD than in SD. Relatively more of the ¹⁴C delivered to the apical bud of G2 peas was transported to flower buds than to young leaves in LD as compared to SD. There was no striking photoperiodic difference in carbon partitioning in genetic lines without the Sn Hr allele combination. The Sn Hr allele combination and photoperiod may regulate the relative strength of reproductive and vegetative sinks. Photoperiodic differences in sink strength early in reproduction suggest that these genes regulate sink strength by affecting the physiology of the whole plant. High vegetative sink strength in SD may maintain assimilate supply to the apical bud, delaying senescence.     

Postflowering photoperiod regulates vegetative growth and reproductive development of soybean

Soybean development is controlled by environmental factors, primarily photoperiod and temperature. To date, photoperiod effects on flowering have been well studied but the performances and mechanism of postflowering photoperiod responses have not been fully understood, especially for the photoperiod effects on vegetative growth after flowering. In the present study, the responses of vegetative growth and reproductive development in soybean to different postflowering photoperiod regimes were investigated in four separate experiments. Three varieties of different maturity groups (MG) including the early (Dongnong 36, MG 000), medium (Dandou 5, MG IV), and late (Zigongdongdou, MG IX) were exposed to two photoperiods, short (10, 12 h) and long (15, 16 or 18 h). The results showed that postflowering photoperiod not only regulated reproductive development but also affected vegetative growth. Even when flowers and pods were removed, short-day (SD) treatment promoted leaf senescence. The onset of leaf senescence among varieties tested appeared to be dependent on photoperiod sensitivity. Leaf senescence of the late-maturing variety of Zigongdongdou (sensitive to photoperiod) was delayed more significantly than that of the medium and early-maturing varieties (less sensitive to photoperiod). Long-day (LD) treatments delayed leaf senescence and seed maturation in the late-maturing variety of Zigongdongdou plants with only the SD-induced leaves produced before flowering. LD treatments imposed from the beginning bloom, beginning pod setting or beginning seed filling delayed leaf senescence and seed maturation of late-maturing soybean variety (Zigongdongdou). Results of night-break with red (R) and far-red (FR) light demonstrated that postflowering photoperiod responses of soybean were R/FR reversible reactions and the phytochromes seemed to be functional as receptors of photoperiod signals even after flowering. It was proposed that the regulation of photoperiod on development of soybean was effective from emergence through maturation, and the postflowering photoperiod signals were also mediated by phytochromes similar to those before flowering. The flowering reversion in late-MG soybean varieties under LD was a direct result of LD and was not due to secondary effect of abscission of pods and flowers. Soybean leaves not only received SD signals but also LD signals; furthermore, the LD effects reversed the SD effects and vice versa.     

Evidence for a graft-transmissible substance which delays apical senescence in Pisum sativum L.

Apical senescence in an early flowering line of pea, G2, is greatly delayed by short days. This behavior is controlled by two dominant genes. Apical senescence of ungrafted, insensitive (I) lines is unaffected by photoperiod. When I-type scions with one of the two required genes were grafted onto G2, apical senescence of the I-type was delayed in short days, but not in long days. Flowering of the I-type was unaffected. The apex of the G2 stock was unaffected as well. Apical senescence of an I-type line lacking both photoperiod genes was not delayed when grafted on G2 in short days. It is concluded that G2 plants grown in short days produce a graft-transmissible factor which delays apical senescence of photoperiodically insensitive lines.     

Reversion of flowering in Glycine Max (Fabaceae)

Photoperiodic changes, if occurring before a commitment to flowering is established, can alter the morphological pattern of plant development. In this study, Glycine max (L.) Merrill cv. Ransom plants were initially grown under an inductive short-day (SD) photoperiod to promote flower evocation and then transferred to a long-day (LD) photoperiod to delay flower development by reestablishing vegetative growth (SD-LD plants). Some plants were transferred back to SD after 4-LD exposures to repromote flowering (SD-LD-SD plants). Alterations in organ initiation patterns, from floral to vegetative and back to floral, are characteristic of a reversion phenomenon. Morphological features that occurred at the shoot apical meristem in SD, LD, SD-LD, and SD-LD-SD plants were observed using scanning electron microscopy (SEM). Reverted plants initiated floral bracts and resumed initiation of trifoliolate leaves in the two-fifths floral phyllotaxy prior to terminal inflorescence development. When these plants matured, leaf-bract intermediates were positioned on the main stem instead of trifoliolate leaves. Plants transferred back to a SD photoperiod flowered earlier than those left in LD conditions. Results indicated that in plants transferred between SDs and LDs, photoperiod can influence organ initiation in florally evoked, but not committed, G. max plants.     

Cell Cycle Responses to Red or Far-red Light, or Darkness, in the Shoot Apex of Silene coeli-rosa L. During Floral Induction

Twenty-eight-day-old plants of Silene coeli-rosa L. were maintainedin short days (SD) for 9 d (0–8) or exposed to 7 longdays (LD), or 7 SD with a 5 min exposure at 1700 h of each dayto far-red (FR), red (R) or 5 min FR/5 min R, or 7 dark-interrupted(di = 1700–1720 h) LD. Treatments were followed by twofurther SD. The mitotic index and G1 and G2 proportions weremeasured in the shoot apices of plants sampled at 2000 h ofeach day of each replicated treatment. Exposure to 7 LD (= 100per cent flowering) resulted in significant increases, relativeto the SD controls, in both the G2 proportion and the mitoticindex on d 0 to 3, 7 and 8. Five minute FR (= 0 per cent flowering)resulted in cell cycle responses similar to those in LD onlyfrom d 0 to 2. R and FR/R (both = 0 per cent flowering) didnot result in any increases in the G2 proportion in the apexapart from d 3 of FR/R. However 5 min FR/5 min R, and to a lesserextent 5 min R, did result in significant increases in the mitoticindex on d 0, 1, 7, and 8. diLD (= 8–10 per cent flowering)also prevented any significant increases in the G2 proportionon d 0 to 3, and 5 to 8 but the mitotic index was again higheron these days compared with control data. Thus the transitionto floral growth for 90 per cent of the plants is associatedwith changes in the cell cycle in the shoot apex measured asincreases in the G2 proportion at 2000 h of LD 0 to 3 and 7to 8. Silene coeli-rosa L., cell cycle, flowering, phytochrome, shoot apex     

Gibberellin Is Involved in the Regulation of Cell Death-mediated Apical Senescence in G2 Pea

Senescence is the process of programmed degradation. The G2 line of pea exhibits apical senescence-delaying phenotype under short-day （SD） conditions, but the mechanism regulating the apical senescence is still largely unknown. Gibberellin （GA） was proved to be able to delay this apical senescence phenotype in G2 pea grown under long-day （LD） conditions. Here we show that the initiation of cell death signals in the terminal floral meristem was involved in the regulation of apical senescence in pea plants. SD signals prevented the formation of the cell death region in the apical mersitem. Moreover, GA3 treatment could effectively inhibit the occurrence of cell death-mediated apical senescence in LD-grown apical buds. Therefore, our data suggest that the prevention of apical senescence in SD-grown G2 pea through GA3 treatment may be largely responsible for the regulation of occurrence of the DNA fragmentation in apical meristem.     

The facultative photoperiodic response in the reproductive development of Amaranthus retroflexus L.: Changes in the dose response during ontogeny

The first inductive (short-day; SD) cycle advanced the initiation of reproductive development, while additional SD cycles progressively reduced the lag phase between the start of induction and initiation. The sensitivity to SD increased during ontogeny in long-days (LD) until even the requirement for the first SD cycle disappeared at the onset of autonomous flowering. In photo-induced plants, the postinitiation rate of elongation of the apex was accelerated as the SD dose was increased, but was progressively slower as the start of induction was delayed closer to autonomous flowering, approaching asymptotically the rate of non-induced controls. The inflorescences were branched in plants growing continuously in LD and unbranched in those growing continously in SD. The subsequent branching of the inflorescence could be repressed by SD at any time prior to autonomous flowering, and the degree of repression increased with the induction dose. After the initial SD cycle, 1–2 additional SD could induce the loss of apical dominance, causing excessive elongation and leaf production in the subjacent branches. Further increase in the SD dose inhibited this elongation by accelerating the transformation of the apices of these branches to the reproductive state.Abbreviations LD long day(s) - SD short day(s) - ContSD continuous short day(s) - RGR relative growth rate     

A kinetic analysis of the facultative photoperiodic response in Amaranthus retroflexus L.

The ontogenetic change taking place in the facultative photoperiodic response of A. retroflexus to inductive short-day (SD) conditions was studied by exposing plants to continuous induction after different initial exposures to long-days (LD), and comparing the kinetics of their developmental responses (cumulative number of plants with reproductive apices, flowering stage, and height of the apical dome). As the plants progressed from emergence to autonomous flowering (i.e., in non-inductive conditions), their response to continuous induction became progressively more rapid. Reproductive development was initiated following a progressively shorter lag-phase after the start of induction, but its subsequent rate remained unchanged. Until the onset of reproductive development, the undifferentiated upper part of the shoot apex (apical dome) elongated much more rapidly in SD than in LD. However, in both cases reproductive development was initiated when the apex had elongated to about the same extent, after which its elongation accelerated considerably, but to similar rates in both photoperiods. The data indicate that progress towards reproductive development takes place in inductive (SD), as well as in non-inductive (LD) photoperiods, but one cycle of the latter is as effective as 0.20–0.25 of a cycle of the former. —Plants induced at different stages in ontogeny started to change their subsequent branching pattern (ratio of leafy to leafless branches) as soon as induction was delayed beyond autonomous flowering.Abbreviations LD long-days - SD short-days - RGR Relative Growth Rate     

Indole-3-acetic acid concentration and ethylene evolution during early fruit development in peach

Ethylene evolution was measured from greenhouse-grown Jerseyglo peach fruits beginning 29 days after anthesis. Indole-3-acetic acid (IAA) levels were measured in the pericarp and seed tissues of individual fruits on a single shoot when variable ethylene evolution was noted. Despite hand-pollinating all flowers on the same day, variability within the shoot existed in fruit fresh weight, IAA levels, and ethylene evolution. Seed IAA concentration increased as fruit and seed fresh weight increased and ranged from 106 to 1572 ng. g^–1. As pericarp fresh weight increased, IAA levels in this tissue decreased. Ethylene evolution rates ranged from 0.21 to 1.07 nl. g.^–1 h^–1 and were not correlated with IAA concentration in seed, pericarp, or the whole fruit. High rates of ethylene evolution from the whole fruit occurred prior to increased IAA concentration in the seed.Fruits were excised from field-grown Redskin peach trees beginning 40 days after full bloom. Fruits from field sampled shoots appeared to be more physiologically advanced than the greenhouse-grown Jerseyglo fruits. Pericarp IAA concentration was low, ranging from 2.8 to 6.5 ng. g^–1. Seed concentrations accounted for 75% of the IAA found in the fruit and ranged from 239 to 1042 ng. g^–1. As with greenhouse-grown samples, whole fruit IAA concentration tended to decrease as fruits increased in fresh weight.     

Rates of cell division in the young prefloral shoot apex ofChrysanthemum segetum L.

Summary The rate of cell division was determined by the colchicine induced metaphase-accumulation technique in the young prefloral shoot apex of the quantitative long-day plantChrysanthemum segetum L. growing under conditions favourable to flowering (16-hour photoperiod; 124Em^–2s^–1; 22 °C). Cell cycle duration was evaluated in relation to the location of the cells in the intact apex. The cell cycle durations were 53.5 hours, 47.4 hours, and 97.7 hours in the axial, lateral and subapical central cells respectively. Compared with previous results, these data give evidence of the major role played by the early increase in cell division rate of axial cells in the new pattern of the prefloral shoot apex at its initial stage of development. By comparison with the vegetative shoot apex, the cell cycle duration was preferentially shortened in the axial zone; it was only slightly altered in the lateral zone while it was lengthened in the vacuolating subapical central cells. In the three zones within the prefloral shoot apex, the duration of mitosis was constant (3.2 to 3.3 hours) and the same as in the vegetative shoot apex.     

Sex-related adaptive responses of Populus cathayana to photoperiod transitions

Populus cathayana Rehd., a dioecious tree species, occupies a wide range of habitats in southwest China. Both males and females were grown under two regimes of photoperiod, from mid-length to short-day photoperiod (SD shift), or to long-day photoperiod (LD shift). SD shift triggered leaf senescence in both males and females by decreasing net photosynthesis rate ( A ), transpiration ( E ), and chlorophyll pigment ( Chl ), non-structural carbohydrate (NSC) and indoleacetic acid (IAA) contents, while increasing abscisic acid (ABA), malonaldehyde (MDA) and free proline (Pro) contents. The antioxidant enzyme (e.g. POD, CAT and SOD) activities and capability to maintain ultrastructural integrity also decreased under SD shift. Males exhibited faster leaf senescence than did females, as shown by greater decreases in A , E , Chl and IAA. However, males maintained a less senescent stage than did females, as indicated by higher values of A , Chl , NSC, IAA and antioxidant enzyme activities. Conversely, A , E , NSC and IAA contents and antioxidant enzyme activities were enhanced by lower O₂^•− in females, whereas reduced by higher O₂^•− in males under LD shift. Such sex-dependent responses of P. cathayana to photoperiod transitions showed that males and females possess different adaptabilities, which may relate to sex-specific leaf senescence speed under changing environments.     

Export of organic materials from developing fruits of pea and its possible relation to apical senescence

In the G2 line of peas (Pisum sativum L.) senescence and death of the apical bud occurs only in long days (LD) in the presence of fruits. Removal of the fruits prevents apical senescence. One possible reason for the senescence-inducing effect of fruit is that the fruits produce a senescence-inducing factor which moves to the apical bud and is responsible for the effect. For this to be possible there must be a transport mechanism by which material may move from the pods to the apex. To examine the extent of fruit export, pods were labeled via photoassimilation of ¹⁴CO₂ beginning 12 days after anthesis. Under LD conditions, 1.14% of label fixed was transported from the pods with only 10.5% of this found in the apical bud and youngest leaves after 48 hours, the remainder being found principally in other developing fruits and mature leaves. During the onset of apical senescence, less total label was actually exported to the apical bud than at other times. In addition, more total export occurred from pods in short days than in LD, with the apical bud receiving a greater percentage than in LD. Thus the amount and distribution of export would not seem to support the idea of specific export of targeted senescence-promoting compounds. Girdling of the fruit peduncle did not change the characteristics of export suggesting movement via an apoplastic xylem pathway.     

Changes in Tuberization and Assimilate Partitioning in Potato (Solanum tuberosum) During the First 18 Days of Photoperiod Treatment

Potato (Solanum tuberosum L.) plants were equilibrated under18-h days (LD) before a subset of the plants was transferredto 10-h photosynthetic periods with either a dark night (SD)or an 8-h dim photoperiod extension with incandescent lamps(DE). Plants were harvested at regular intervals for growthanalysis during the 18 d after transfer. Leaf area increasedrapidly under SD and LD but was inhibited under DE. Internodeelongation was similar under SD and LD, but much higher underDE. Stem d. wts were lowest under SD. Axillary branching wasgenerally greatest under LD. Total shoot weights were greatestunder LD. Total shoot weights were similar under SD to thoseunder DE, even though within 18 d of transfer as much as one-thirdof the biomass of SD plants was in tubers. Tuber initiationwas later under LD than under SD, and was delayed even moreby DE. High temperature increased the delay in tuberizationfrom LD. The early tuber initiation under SD was concurrentwith a rapid increase in leaf area under SD, not with an earlycessation of leaf growth. This was contrary to assumptions basedupon studies of long-term effects of photoperiod. The resultanthigh sink strength under SD contributed to the greater efficiencyof biomass production. Potato, Solanum tuberosum L. cv. Norchip, photoperiod, temperature, morphology, tuberization, growth analysis, biomass partitioning, sink strength, leaf area, short term effects     

Effect of Fruits on Dormancy and Abscisic Acid Concentration in the Axillary Buds of Phaseolus vulgaris L

The mechanism regulating the growth of adult plants in two determinate bean (Phaseolus vulgaris L.) cultivars was investigated. “Redkloud” plants flowered, formed fruits, and ceased shoot growth earlier than “Redkote” plants. Redkloud attained a smaller plant size, compared to Redkote, by imposing dormancy on axillary buds at an earlier age. In both cultivars, cessation of bud growth coincided with maximum combined fruit length per plant. Removal of fruits caused resumption of axillary bud growth within 4 to 5 days. The amount of new growth induced by fruit removal depended on the cultivar and plant age. In fully developed Redkloud plants, where shoot growth had already ceased, total leaf and shoot number per plant nearly doubled within 2 weeks following fruit removal. A much smaller response was observed in the still growing Redkote plants. Fruits, therefore, are assumed to play a major role in the regulation of shoot growth and total plant size through the control of axillary bud dormancy. It seems that smaller plant size, earlier maturity, and earlier senescence of Redkloud, compared to Redkote, were the result of earlier flowering, and accomplished in part through the growth-inhibiting action of fruits.     

Changes in the Pattern of Cell Division in the Shoot and Root Meristems of Lolium perenne during the Transition from Vegetative to Floral Growth

For Lolium perenne cv. Cropper, a system which resulted in 100%flowering comprised 90 short days (SD) at 4 ?C (vernalization)and 30 SD at 18 ?C followed by 8 long days (LD). The mitoticindex and G1 and G2 percentages were measured in the shoot androot apices of plants following 2, 5 or 8 LD and in SD controlssampled at the beginning and end of induction. Identical measurementswere made in plants given 48 SD at 18 ?C followed by 2, 5 or8 LD; plants remained vegetative in response to this treatmentlacking vernalization. Significant increases in both mitoticindex and meristem size occurred in the shoot apex in LD followingthe vernalizing, but not the non-vernalizing, treatment. A clusterof mitoses in the apical dome of the shoot apex was unique tothe vernalized plants given 5 or 8 LD. However, an increasein root meristem size occurred regardless of vernalization,but a significant increase in the mitotic index was limitedto vernalized plants given 5 or 8 LD. Whilst the vernalization-LDtreatment resulted in an increase in the G2 percentage in theshoot apex following 2, 5 or 8 LD, no such alteration was observedin the root meristem. Thus, the changes to the cell cycle whichcorrelated with flowering were increased mitotic indices andG2 percentages in the shoot apex at each sampling time and increasedmitotic indices in the root apex following 5 and 8 LD. Key words: Cell division, flowering, Lolium perenne L.     

The role of auxin and sugar signaling in dominance inhibition of inflorescence growth by fruit load

Dominance inhibition of shoot growth by fruit load is a major factor that regulates shoot architecture and limits yield in agriculture and horticulture crops. In annual plants, the inhibition of inflorescence growth by fruit load occurs at a late stage of inflorescence development termed the end of flowering transition. Physiological studies show this transition is mediated by production and export of auxin from developing fruits in close proximity to the inflorescence apex. In the meristem, cessation of inflorescence growth is controlled in part by the age-dependent pathway, which regulates the timing of arrest. Here, we show the end of flowering transition is a two-step process in Arabidopsis (Arabidopsis thaliana). The first stage is characterized by a cessation of inflorescence growth, while immature fruit continues to develop. At this stage, dominance inhibition of inflorescence growth by fruit load is associated with a selective dampening of auxin transport in the apical region of the stem. Subsequently, an increase in auxin response in the vascular tissues of the apical stem where developing fruits are attached marks the second stage for the end of flowering transition. Similar to the vegetative and floral transition, the end of flowering transition is associated with a change in sugar signaling and metabolism in the inflorescence apex. Taken together, our results suggest that during the end of flowering transition, dominance inhibition of inflorescence shoot growth by fruit load is mediated by auxin and sugar signaling.

Dominance inhibition of inflorescence shoot growth by fruit load involves auxin and sugar signaling during the end of flowering transition.     

Modification of Seed Growth in Soybean by Physical Restraint: Effect on Leaf Senescence

Crafts-Brandner, S. J. and Egli, D. B. 1987. Modification ofseed growth in soybean by physical restraint. Effect on leafsenescence.—J. exp. Bot. 38: 2043–2049. The effect of total plant sink size on leaf senescence in soybean[Glycine max (L.) Merrill] was investigated by using a simple,non-destructive method to decrease seed growth rate and totalplant fruit sink size without altering fruit or seed number.The treatment consisted of placing plastic pod restriction devices(PPRD), which were made from plastic drinking straws (6·35mm diameter), over the fruits so that all of the seeds werecontained within the PPRD's. The treatment did not alter thetime of initiation of leaf senescence for two cultivars (McCalland Maple Amber), but decreased the rate of leaf senescencebased on declines in chlorophyll, ribulose-l,5-hi'sphosphatecarboxylase/oxygenase level and carbon dioxide exchange rate.The treatment also delayed seed maturation. At the time of seedmaturation, the plants still retained green leaves. In a separate experiment, one seed in each fruit (40% of theseeds on the plant) was not restrained by the PPRD's. This treatmentled to an intermediate rate of leaf senescence compared to controland complete seed restriction treatments. The results indicatedthat, for the cultivars examined (1) leaf senescence was initiatedat the same time regardless of sink size (2) the rate of leafsenescence could be modified by altering sink size and (3) seedmaturation could occur without complete leaf yellowing and leafabscission. The effect of the PPRD treatments on leaf senescencewere similar to results obtained when fruits were physicallyremoved, which indicated that physical removal of fruits doesnot lead to artefacts due to wounding of the plants. Key words: Glycine max L, senescence, source-sink     

Ageing of theSilene coeli-rosa L. shoot apex under non-inductive conditions: Changes in morphology,mitotic index,and polypeptide composition

Summary Ageing was studied in the shoot apex of the long day plant,Silene coeli-rosa by maintaining it in non-inductive short day conditions for 170 days. The dimensions, the zonation, and the polypeptidic pattern of the shoot apex, and the rate of leaf initiation were altered in 170-day-old plants compared with young plants grown under the same conditions (28 days). In aged plants, the number of cells increased in all shoot apical zones and, notably, the mitotic index increased in the axial zone; however, the rate of leaf initiation slowed down. These changes showed some similarities to those during the intermediate phase in quantitative photoperiodic species. The two-dimensional mini-gel electrophoretic study of protein extracts from shoot apices of young and ageing plants maintained in non-inductive conditions revealed 489 common polypeptidic spots, 13 unique to the young state and 24 new ones specific to aged plants. The spots characteristic for each state represented only 3.6% of the total identified polypeptides, but apical development under non-inductive conditions was characterized by qualitative changes in the polypeptide complement.Abbreviations C nuclear DNA complement - 1D gel first dimension gel - LD long day - NEPHGE non equilibrium pH gradient electrophoresis - SD short day - SDS sodium dodecyl sulfate - TCA trichloracetic acid