Light and Shade Effects on Abscission and C-Photoassimilate Partitioning among Reproductive Structures in Soybean

Field experiments were conducted in 1981 and 1982 to study the effects of low-irradiance supplemental light on soybean (Glycine max [L.] Merr. cv Evans) flower and pod abscission. Cool-white and red fluorescent lights illuminated the lower part of the soybean canopy during daylight hours for 3 weeks late in flowering. At the same time, flowers and young pods on half the plants were shaded with aluminum foil. Flowers were tagged at anthesis and monitored through abscission or pod maturity.

Responses to red and white lights were similar. Supplemental light tended to reduce abscission and increase seed weight per node compared to natural light. Shading flowers and pods increased abscission and reduced seed weight per node. Number of flowers produced per node, individual seed weight, and seeds per pod were not affected by light or shade treatments.

Further studies examined the effects of shading reproductive structures on their capacity to accumulate ¹⁴C-photoassimilates. Individual leaves were pulse labeled with ¹⁴CO₂ 1, 2, and 4 weeks post anthesis. Flowers and pods in the axil of the labeled leaf were covered with aluminum foil 0, 24, 72, and 120 hours before pulsing.

Shading flowers and pods resulted in a 30% reduction in the relative amount of radiolabel accumulated from the source leaf. The reduction in ¹⁴C accumulation due to shading was evident regardless of the length of the shading period and was most pronounced when the shades were applied early in reproductive development. We conclude that light perceived by soybean flowers and young pods has a role in regulating both their abscission and their capacity to accumulate photoassimilates.

     

A Flower and Pod Staging System for Soybean

Flower and pod abscission limit soybean yield. A system forquantifying flower and pod development based on the morphologicalappearance of the flower prior to and following anthesis hasbeen developed to aid in studies of pod abscission. Changesin 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 internalfeatures for each stage of development. From anthesis to podset, pistil length and weight increase almost two- and fivefold,respectively, and ovule development progresses from unfertilizedegg cells to embryos surrounded by cellular endosperm. Pod determinedare correlated with ovule length and width and embryo cell number.Flower and pod stages can be determined in situ, thus permittingnon-destructive observation and experimental manipulation offlowers or pods without necessarily impeding their development.Stages have been identified that indicate precisely when podset occurs and when young pods cease growing and ultimatelyabscise. This system of flower and pod staging is useful instudies designed to assess effects of abiotic or biotic stressand genetic factors on pod set and abortion. Abscission, anthesis, Glycine max (L.) Merr, embryo development, pod set     

Effect of Removal of Flower Buds, Open Flowers, Young Pods and Shoot Apex on Growth and Pod Set in Soybean

The complete removal of the reproductive structures once andshoot apices of soybeans (Glycine max L. Merrill) during earlyanthesis but before the rapid seed development stage significantlyincreased flowering and pod set in greenhouse and field grownplants. The treated plants had darker green leaves, shorterstems and petioles and retained their chlorophyll content longerthan control plants. Pod maturation was also delayed. Althoughdecapitation and the removal of reproductive structures increasedthe number of 3- or more-seeded pods in all varieties tested,seed weight per plant was not consistently increased. The possibleinvolvement of endogenous hormones in pod set and multi-loculepod production in soybeans is discussed. Key words: Glycine max (L.) Merr, Reproductive structures, Shoot apex, Growth, Flowering, Pod set, Multi-locule pods     

不同时期叶喷植物生长调节剂对大豆花荚脱落率及多聚半乳糖醛酸酶活性的影响

在大田条件下,以大豆品种‘合丰50＇为材料,比较研究了在V3（第3节龄期,三叶期）、R1（初花期）和R3（始荚期）期叶面喷施DTA-6、S_（3307）和TIBA三种植物生长调节剂对大豆花荚脱落率及多聚半乳糖醛酸酶活性的影响。结果表明：V3期叶喷TIBA、S_（3307）、DTA降低了大豆花荚脱落率,降低了大豆花荚和脱落花荚多聚半乳糖醛酸酶活性;R1期叶喷植物生长调节剂显著降低了大豆花荚及脱落花荚中多聚半乳糖醛酸酶活性,以DTA-6调控效果最佳,S_（3307）次之;R3期叶喷植物生长调节剂降低了大豆荚及落荚的多聚半乳糖醛酸酶活性,以DTA-6调控效果最佳,TIBA次之。综合分析表明,V3、R1和R3期叶面喷施植物生长调节剂能够降低大豆花荚脱落率及多聚半乳糖醛酸酶活性,对大豆花荚的脱落有一定的调控作用,有利于提高产量,其综合调控效果为,V3期：S_（3307）〉DTA-6〉TIBA〉CK;R1期：DTA-6〉TIBA〉S_（3307）〉CK;R3期：DTA-6〉TIBA〉S_（3307）〉CK。     

Carbon Exchange Rate of Intact Individual Soya Bean Pods. 1. Response to Step Changes in Light and Temperature

Carbon exchange rates (CER) of individual intact field-grownsoya bean [Glycine max (L.) Merr.] pods were measured continuouslywith a mobile gas analysis laboratory. Conditions in pod chamberssimulated those experienced normally by pods except for experimentalmodification of incident radiation or pod temperature. Undernormal conditions, CER (where positive CER represents CO₂ evolution)fluctuated diurnally with a morning rise followed by a slowafternoon and evening decline which was similar among pods whichwere measured simultaneously. The frequency of measurementspermitted detection of rapid CER responses to step changes inlight and pod temperature. CER rapidly decreased and increasedwhen the chamber was alternately exposed to full sunlight andcomplete darkness, respectively. CER responded similarly tosteps up [from ambient to elevated (+ 10°C) temperature]and steps down (from elevated to ambient temperature), respectively.Thus, a temperature sensitive process which regulated pod CERwas located within the pod. CER ranged from less than 0·1to more than 1·2 mg CO₂ h^–1 pod^–1 over theperiod of rapid dry-matter accumulation. Glycine max (L.) Merr., Soya bean, carbon exchange rate, light, temperature     

The Physiological Basis for Cytokinin Induced Increases in Pod Set in IX93-100 Soybeans

Previous investigations have shown the feasibility of increasing pod number on legumes by the application of 6-benzylaminopurine (BA) directly to the raceme. These investigations were designed to determine what reproductive parameter was affected by cytokinin application, and if these applications were overcoming a deficiency in root-produced cytokinins during late flowering. Five individual main stem racemes on greenhouse grown soybeans (Glycine max L. Merr.) were treated with 2 millimolar BA. A single application of BA when pods appeared at 25 to 50% of the proximal floral positions resulted in a 58% increase in pod set due primarily to a 33% reduction in floral abscission. Applications of BA at later intervals also resulted in significant reductions in total abscission. When three applications of BA were imposed on the upper five nodes of field grown soybeans, total pod number and seed weight were significantly increased in this section of the canopy by 27 and 18%, respectively. Throughout the flowering period, root pressure exudate was sampled for the subsequent separation and quantification of zeatin, dihydrozeatin, zeatin riboside, dihydrozeatin riboside, and isopentenyladenine. Total cytokinin flux peaked from 0 to 9 days after flowering began, and then dropped to one-half of this level by 15 days postanthesis. The probability that a flower would initiate a pod was directly related to the concentration of total cytokinins present in the exudate when the flower opened.     

Pedicel abscission and rachis morphology of soybean as influenced by benzylaminopurine and the presence of pods

The cytokinin 6-benzylaminopurine (BAP) increases pod set of soybean Glycine max (L.) Merr. This study was performed to determine the effect of site and method of BAP application on pedicel abscission and the accompanying changes in rachis anatomy. Spraying racemes with BAP in solution, or applying in a lanolin suspension to proximal nodes on a rachis where proximal pedicels had been excised, delayed pedicel abscission at distal nodes. Applying BAP in lanolin to distal pedicels following flower excision failed to delay their abscission. BAP caused rachis swelling only when pods were present, but BAP could delay pedicel abscission either in the presence or absence of pods. These results suggest that rachis swelling following BAP treatment does not have a causal relationship to a delay or decrease of pedicel abscission.Alabama Agricultural Experiment Station Journal No. 6-912843P.     

Factors Affecting Shedding of Flowers in Soybean (Glycine max (L.) Merrill)

Flower shedding in soybean, Glycine max (L.) Merrill, was studiedusing cultivar ‘Clark’, isoline E₁t, which has relativelylong racemes for convenient identification and observation ofindividual flowers. On each raceme studied, pod set was greatestat the proximal (basal) positions, whereas shedding was greatestat the most distal positions. When proximal flowers were removedas they reached anthesis, pod set increased at the more distalpositions. Pod set was increased in some instances by applicationof water directly to the ovaries as a drop in the calyx cup.Peroxidase activity changed in parallel with ovary development,increasing rapidly in growing pods but not in shedding flowers.Increases in flower peroxidase was mainly in ovary walls. Flowerstaken at or near anthesis from positions with high percent podset could be grown in vitro with especially good ovary enlargement,whereas ovaries in flowers taken from positions of low pod setdid not enlarge in culture. Unidentified substances were extracted from young pods which,when incorporated into lanolin and tested in an in situ bioassay,could mimic the effect of proximal flowers in inducing sheddingof distal flowers. Indole-3-acetic acid resembled the extractedmaterials in inducing shedding, but differed by eliciting side-effectsthat extracts did not. The growth substances abscisic acid,gibberellic acid, and benzyladenine did not promote sheddingin the in situ test. The evidence was taken to indicate that soybean flower sheddingis induced in distal flowers by substances from the more proximal,fertilized ovaries, and that this is possibly due to interferencewith some of the intense metabolic changes that follow pollinationand fertilization.     

The Effect of Temperature on the Production and Abscission of Flowers and Pods in Snap Bean (Phaseolus vulgaris L.)

The effect of temperature on production and abscission of flowerbuds, flowers and pods was studied in a determinate snap-beancultivar (cv. Tenderette). Under moderate temperature (e.g.27/17 °C) the onset of pod development was associated withcessation of flower bud production and with enhanced abscissionof flower buds. Raising night temperature from 17 °C to27 °C strongly reduced pod production, mature pod size andseeds per pod, while an increase in day temperature from 22°C to 32 °C had smaller and less consistent effects.Pod production under high night temperature was not constrainedby flower production since 27 °C at night promoted branchingand flower bud appearance. Under 32/27 °C day/night temperaturethe large reduction in pod set was due to enhanced abscissionof flower buds, flowers and young pods (< 3 cm). Flowershad the highest relative abscission followed by young pods andflower buds. Therefore, the onset of anthesis and of pod developmentwere the plant stages most sensitive to night temperature. Podslarger than 3 cm did not abscise but usually aborted and shrivelledunder high night temperature. The effects of 32/27 °C werenot due to transient water stresses and were observed even undercontinuous irrigation and mist-spraying. High temperature, flower production, pod set, seed set, abscission, snap bean, Phaseolus vulgaris L., cv. Tenderette     

Factors affecting the Abscission of Reproductive Organs in Yellow Lupms (Lupinus luteus L.): II. THE EFFECTS OF GROWTH SUBSTANCES, DEFOLIATION, AND REMOVAL OF LATERAL GROWTH

Abscission of flowers in Lupinus luteus L. (var. Weiko II) withoutgrowth of ovaries is followed by abscission of small pods (15–20mm. long). Normally flower abscission is much more pronouncedthan pod abscission. Abscission was delayed on plants from which laterals or theirterminal and axifliary buds were removed. Flower abscissionwas not affected, but pod abscission increased as a result ofdefoliation. When flowers at the base of the main inflorescence were replacedby auxins and anti-auxins flower abscission was induced in eitheran auxin pattern in which most of the flowers near the siteof application dropped, and pods developed on the apical whorls,or an anti-auxin pattern in which pods developed on basal whorlsnear the site of application but not higher up. The anti-auxinpattern was similar to the pattern of abscission normally inducedby developing pods on basal whorls. -Naphthylacetic acid (NAA) was much more effective in inducingabscission than ß-indolylacetic acid (IAA). 2:3:5-triiodobenzoicacid (TIBA), NAA, and IAA applied in mixtures at various concentrationsacted mainly antagonistically, i.e. the abscission-inducingeffect of NAA and LAA was depressed in basal whorls, and inapical whorls the effect of TIBA was less prevalent. Consequentlythe effect of the mixtures on the total number of pods was aboutequal to that of the most active component by itself. All growth substances seemed to move much more efficiently inacropetal direction than in basipetal direction in the flowerstalk. Transport in lateral direction was very limited. The effect of growth substances applied on laterals was enhancedby defoliating the main 8tem. The influence of assimilates on flower and pod abscission andtransport of growth substances is discussed.     

Cytokinin Regulation of Flower and Pod Set in Soybeans (Glycine max(L.) Merr.)

Exogenous application of cytokinin to raceme tissues of soybean(Glycine max(L.) Merr.) has been shown to stimulate flower productionand to prevent flower abortion. The effects of these hormoneapplications have been ascertained for treated tissues, butthe effects of cytokinins on total seed yields in treated plantshave not been evaluated. Our objectives were to examine theeffects of systemic cytokinin applications on soybean yieldsusing an experimental line of soybeans, SD-87001, that has beenshown to be highly sensitive to exogenous cytokinin application.Soybeans were grown hydroponically or in pots in the greenhouse,and 6-benzylaminopurine (BA) was introduced into the xylem streamthrough a cotton wick for 2 weeks during anthesis. After theplants had matured, the number of pods, seeds per pod, and thetotal seed weight per plant were measured. In the greenhouse,application of 3.4 x 10^-7 moles of BA resulted in a 79% increasein seed yield compared with controls. Results of field trialsshowed much greater variability within treatments, with consistent,but non-significant increases in seed number and total yieldsof about 3%. Data suggest that cytokinin levels play a significantrole in determining total yield in soybeans, and that increasingcytokinin concentrations in certain environments may resultin increased total seed production. Copyright 2001 Annals ofBotany Company Glycine max, soybean, flower abortion, cytokinin, 6-benzylaminopurine, hydroponic, seed yield, wicking     

Soya Bean Seed Growth and Maturation by In Vitro Pod Culture

Immature Glycine max (L.) Merr. seeds initially at 50–70mg fresh weight were successfully grown and matured in vitroin detached pods. Surface sterilized pods were floated in aliquid medium containing 5 per cent sucrose, minerals, and glutaminein 125 ml Erlenmeyer flasks and incubated at 25 °C under350–400 µE m^–1 s^–1 white light. Seedswhich were matured in vitro increased tenfold in dry weight,were visually similar to commercial seeds of the same size,were tolerant to desiccation and germinated with normal seedlinggrowth. Excised pods transported dye from the pedicel to thegrowing seed within 120 min. Soya bean pod culture is a usefultechnique to study the influence of single or combinations ofchemical or environmental parameters on regulation of seed growth,seed maturation, and subsequent germination events without theconfounding interactions with the mother plant. Glycine max (L.) Merr., soya bean, pod culture, seed culture, seed growth, seed maturation, germination     

Probing Monocarpic Senescence and Pod Development Through Manipulation of Cytokinin and Mineral Supplies in Soybean Explants

Defined solutions containing cytokinin and/or mineral nutrientswere supplied in lieu of the roots through the cut stem baseof soybean explants (a leaf with associated pod and subtendingstem segment) in order to analyze the roles of cytokinin andmineral nutrients from the roots in pod development and foliarmaintenance. In explants cut at early-mid podfill, supplyingonly H₂O accelerated leaf senescence and pod maturation anddecreased seed d. wt relative to comparable parts of intactplants. Zeatin (Z) and/or minerals not only delayed leaf yellowingand the decline in foliar chlorophyll levels and photosyntheticrates but also inhibited leaflet and petiole abscission relativeto H₂O controls. Even large declines in foliar assimilatoryprocesses did not necessarily lead to abscission. Z and/or mineralsalso increased stomatal conductivity throughout podfill. Z showedsome positive synergistic effects with minerals on leaf maintenance.Pod wall, cotyledon and radicle yellowing were delayed by Zand/or minerals but not as much as leaf senescence. Mineralsonly or Z +minerals prolonged seed d. wt accumulation and increasedfinal dry seed wt to a level similar to that for intact plants.Seed growth showed a complex interrelation with pod wall andleaf f. wt and d. wt changes. A decline in cytokinin and mineralflux from the roots appears to be important for pod-inducedleaf senescence; however, pod development, foliar senescenceand their component processes may be affected differently. Thus,even though the explant is a physiological/nutritional moduleof the whole plant, it is influenced by cytokinin and mineralsfrom the roots and therefore only semiautonomous. Glycine max L. Merr. cv. Anoka, soybean, abscission, cytokinin, chlorophyll, mineral nutrients, seed development, semiautonomous physiological modules, senescence, stomatal resistance     

Auxins,ABA and gibberellin-like activity in abscising and non-abscising flowers and pods of Vicia faba L.

Abscission probability varies among floral positions within inflorescences of Vicia faba L. Flowers from proximal positions have a greater chance to develop into mature pods than flowers from more distal positions which normally abscise either as older flowers or as young pods. In three field experiments with the indeterminate single stem variety Herz-Freya, changes in the contents of extractable auxins, abscisic acid (ABA) and gibberellins in flowers and pods during their development, and their possible influence on abscission were investigated.Inflorescences at different positions along the stem were divided into the two proximal and the remaining fruits. The content of all three hormones was at a low level during flower development, increased greatly in parallel with dry matter accumulation in the young pods, and then decreased to maturity. The first hormone to increase in the fruits was auxin and this took place when abscission from the distal positions began. ABA and gibberellins at this time were still at a low level. This ontogenic course of hormone production was very similar in fruits of both positions within an inflorescence, but in flowers and young pods from proximal positions, auxin content in most inflorescences was greater than in those from the abscising distal positions. No such positional differences were observed with ABA and gibberellins. Decapitation of the plants reduced flower and pod drop from the remaining reproductive nodes. Although decapitation resulted in less abscission among distal flowers and young pods from these nodes, it did not affect the ontogenic course of auxin and ABA production in these fruits.     

The Effect of Temperature on the Production and Abscission of Flowers and Pods in Snap Bean (Phaseolus vulgaris L.)

The effect of temperature on production and abscission of flowerbuds, flowers and pods was studied in a determinate snap-beancultivar (cv. Tenderette). Under moderate temperature (e.g.27/17°C) the onset of pod development was associated withcessation of flower bud production and with enhanced abscissionof flower buds. Raising night temperature from 17°C to 27°Cstrongly reduced pod production, mature pod size and seeds perpod, while an increase in day temperature from 22°C to 32°Chad smaller and less consistent effects. Pod production underhigh night temperature was not constrained by flower productionsince 27°C at night promoted branching and flower bud appearance.Under 32/27°C day/night temperature the large reductionin pod set was due to enhanced abscission of flower buds, flowersand young pods ( 3 cm). Flowers had the highest relative abscissionfollowed by young pods and flower buds. Therefore, the onsetof anthesis and of pod development were the plant stages mostsensitive to night temperature. Pods larger than 3 cm did notabscise but usually aborted and shrivelled under high nighttemperature. The effects of 32/27°C were not due to transientwater stresses and were observed even under continuous irrigationand mist-spraying. High temperature, flower production, pod set, seed set, abscission, snap bean, Phaseolus vulgaris L, Tenderette     

Records of Source--Sink Relations by Means of Respiration Measurements

A method for recording respiration rates of attached singlesoybean pods is described. By means of such records source-sinkrelations can be observed over an extended period of time ifphotosynthesis of leaves is recorded simultaneously. It is shownthat there are direct influences on respiration, such as changesin temperature and indirect effects which influence primarilythe assimilate influx into the pods, e.g. light and competitionbetween pods. The shading of a single leaf next to the pod has only a smalleffect because the pod is supplied by more than one leaf. Bygirdling the plants, the export-import conditions can be studiedon a single leaf as source and a single pod as sink. The resultsshow that a trifoliate fully-grown leaf produces more assimilatethan can be used by a single pod. If only one pod is growingwithin the girdled area then starch is accumulated and the photosyntheticrate of the leaf is greatly reduced. The respiration rate ofthe pod is only slightly increased, in spite of the abundantavailability of assimilates. It appears therefore, that thefilling rate of pods is determined mainly by the capacity ofthe pod to off-load the phloem, and cannot be increased beyonda certain level by additional sucrose influx. Our results show that, using this method, the source-sink relationscan be recorded qualitatively over time periods of 3–4weeks. Key words: Source-sink relations, pod respiration, Glycine max, pod filling, photosynthesis     

Effect of Temporary Chilling on Foliar and Caulinary Growth and Productivity in Soybean (Glycine max)

The effects of chilling on the apical bud were investigatedin soybean. A temperature of 6 °C was applied to leavesI and 2 and the apex for 12 d as soon as leaf 2 appeared. Thegrowth of the foliar and internodal series was analysed usingNelder's logistics. Chilling decreased the number of neoformed phytomers as wellas their rate of appearance. Schematically, the effect of chillingon growth is characterized by an inhibition of leaves and astimulation of internodes. However, the changes in the adultdimensions, and in the kinetic parameters (various durationsand growth rates), depend on the rank of the organ on the axis.Branching was markedly decreased at some nodes. The overallfructification of the main axis remained unchanged, but thedistribution of the seeds on the axis and the repartition betweenaxis and branches were markedly modified. These data clearly show (i) the importance of the position effecton the nature and the intensity of the responses and (ii) theabsence of any return to a normal growth pattern. Thus, a transientand relatively localized thermal stress can disturb the wholeontogenesis. Glycine max, soybean, growth kinetics, development, leaf, shoot, chilling     

Preferential Loss of an Abundant Storage Protein from Soybean Pods during Seed Development

A temporary vegetative storage protein, composed of similar 25 kilodalton and 27 kilodalton subunits, was found to be abundant in soybean (Glycine max (L.) Herr. var Hobbit) leaves, stems, pods, flower petals, germinated cotyledons, and less abundant in roots, nodules and seeds. Total pod protein was highest at 3 weeks after flowering and declined by 37% within 3 weeks during seed development. During this time the vegetative storage protein declined from 18% to 1.5% of the total pod protein and accounted for 45% of the protein lost from pods. This indicates that the vegetative storage protein makes a significant contribution to the pool of nutrients mobilized from pods for transport to developing seeds.