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.     

Influence of 6-Benzylaminopurine on Fruit-Set and Seed Development in Two Soybean, Glycine max (L.) Merr. Genotypes

The influence of 6-benzylaminopurine (BA) on the premature abscission of developing soybean, Glycine max (L.) Merr. fruits of 2 genotypes was studied. BA was applied during the critical period of fruit-setting. The tested concentration range of BA was from 1 micromolar to 5 millimolar; 2 millimolar was optimal. Spray application of 2 millimolar BA to terminal inflorescences at the R₃ developmental stage of field-grown soybeans significantly increased fruit-set and seed yield of the Shore genotype during three growing seasons. In contrast, the Essex genotype gave significant responses two out of three seasons. The response of Shore was generally more pronounced than that of Essex. The apical fruits on the inflorescences gave the greatest response to BA. Seed weight increase was apparent 3-4 weeks after BA treatment.     

Partitioning and Utilization of Photosynthate Produced at Different Growth Stages after Anthesis in Soybean (Glycine max L. Merr.): Analysis by Long-term 13C-Labelling Experiments

Yamagata, M., Kouchi, H. and Yoneyama, T. 1987. Partitioningand utilization of photosynthate produced at different growthstages after anthesis in soybean (Glycine max L. Merr.): Analysisby long term ¹³C-labelling experiments.—J. exp. Bot. 38:1247–1259. Soybean (Glycine max L. Merr. var. Akishirome) plants were allowedto assimilate ¹³CO₂ with a constant specific activity for 10h at different growth stages (a total of seven times at aboutone week intervals) after anthesis. The plants were harvestedperiodically until the time of full maturity and the partitioningof ¹³C into individual plant parts was investigated with anemphasis on the contribution of carbon assimilated at differentgrowth stages to the seed formation. Carbon assimilated at the middle to late seed-filling stagecontributed most to the seed production; one day contributionaccounted for 3–4% in total carbon of the seed at fullmaturity. Integrated contribution of carbon assimilated afteranthesis was estimated as 96% of the final seed carbon. An approximationbased on the temporal data of the incorporation of labelledcarbon into the seeds indicates that 77% of the final seed carboncame from direct transfer of current photosynthate from sourceleaves, which occurred within a few days after the photosyntheticfixation, while the rest originated from remobilization of carbonreserved mainly in leaves and stems plus petioles. In comparison with the total carbon accumulation in the seeds,protein carbon in the seeds was relatively more dependent onphotosynthate produced during the early period of reproductivegrowth stage, whereas lipid carbon was more dependent on photosynthateproduced during the later reproductive stage. Key words: Photosynthate partitioning, soybean (Glycine max L. Merr.), ¹³CO₂ assimilation, seed formation     

Control of Seed Growth in Soya Beans [Glycine max (L.) Merrill]

The seed is the primary sink for photosynthate during reproductivegrowth and an understanding of the mechanisms controlling therate of seed growth is necessary to understand completely theyield production process. The growth rate of individual seedsof seven soya bean [Glycine max (L.) Merrill] cultivars withgenetic differences in seed size varied from 10.8 to 3.9 mgseed^–1 day^–1. The growth rates were highly correlatedwith final seed size. The growth rate of cotyledons culturedin a complete nutrient medium was highly correlated with thegrowth rate of seeds developing on the plant and with finalseed size. The number of cells per seed in the cotyledons variedfrom 10.2 to 5.7 x 10⁶ across the seven cultivars. The numberof cells per seed in the cotyledons was significantly correlatedwith final seed size and the seed growth rate both on the plantand in the culture medium. The data suggest that genetic differencesin seed growth rates are controlled by the cotyledons and thenumber of cells in the cotyledons may be the mechanism of control. Glycine max L., soya bean, seed size, growth rate, cell number, sink activity     

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     

Seed Water Relations and the Regulation of the Duration of Seed Growth in Soybean

Soybean [Glycine max (L.) Merrill] seeds and cotyledons weregrown in an in vitro culture system to investigate the relationshipsbetween cell expansion (net water uptake by the seed) and drymatter accumulation. Seeds or cotyledons grown in a completenutrient medium containing 200 mol m^–3 sucrose continueddry matter accumulation for up to 16 d after in planta seedsreached physiological maturity (maximum seed dry weight). Seedor cotyledon water content increased throughout the cultureperiod and the water concentration remained above 600 g kg^–1fresh weight. These data indicate that the cessation of seeddry matter accumulation is controlled by the physiological environmentof the seed and is not a pre-determined seed characteristic.Adding 600 mol m^–3 mannitol to the medium caused a decreasein seed water content and concentration. Seeds in this mediumstopped accumulating dry matter at a water concentration ofapproximately 550 g kg^–1. The data suggest that dry matteraccumulation by soybean seeds can continue only as long as thereis a net uptake of water to drive cell expansion. In the absenceof a net water uptake, continued dry matter accumulation causesdesiccation which triggers maturation. Key words: Glycine max (L.) Merrill, solution culture, duration of seed growth, water content, dry matter accumulation     

Photoperiodically Induced Changes in Seed Growth Rate of Soybean as Related to Endogenous Concentrations of ABA and Sucrose in Seed Tissues

Short-day photoperiods can increase the partitioning of assimilatesto filling seeds of soybean (Glycine max L. Merr.), resultingin higher seed growth rates. The plant growth substance ABAhas been implicated in the regulation of assimilate transferwithin filling soybean seeds. Thus, we hypothesized that anincreased concentration of endogenous ABA in seeds may enhancesucrose accumulation and seed growth rate of soybeans exposedto short-day photoperiods. Plants of cv. Hood 75 were grownin a greenhouse under an 8-h short-day photoperiod (SD) until11 d after anthesis (DAA) of the first flower, when half ofthe plants were transferred to a night-interruption (NI) treatment(3 h of low-intensity light inserted into the middle of thedark period). Plants remaining in SD throughout seed developmenthad seed growth rates 43% higher than that of plants shiftedto NI (7·6 mg seed^–1 d^–1 vs. 5·3 mgseed^–1 d^–1). On a tissue-water basis, the concentrationof ABA in SD seeds increased rapidly from 7.6 µmol l^–1at 11 DAA to 65·2 µmol l^–1 at 18 DAA, butthen declined to 6·6 µmol l^–1 by 39 DAA.In contrast, the concentration of ABA increased more slowlyin NI seeds, reaching only 47·4 µmol l^–1by 18 DAA, peaking at 57·0 µmol l^–1 on 25DAA, and declining to 10·2 µmol l^–1 by 39DAA. The concentration of sucrose in SD embryos peaked at 73·5mmol l^–1 on 25 DAA and remained relatively constant forthe remainder of the seed-filling period. In NI, the concentrationof sucrose reached only 38·3 mmol 1^–1 by 25 DAA,and peaked at 61·5 µmol l^–1 on 32 DAA. Thusin both SD and NI, sucrose accumulated in embryos only afterthe peak in ABA concentration, suggesting that ABA may havestimulated sucrose movement to the seeds. The earlier accumulationof ABA and sucrose in SD suggests that ABA may have increasedassimilate availability during the critical cell-division period,thus regulating cotyledon cell number and subsequent seed growthrate for the remainder of the seed-filling period. Glycine max L. Merr. cv. Hood 75, soybean, assimilate partitioning, abscisic acid, photoperiod, source-sink     

Moisture Loss as a Prerequisite for Seedling Growth in Soybean Seeds (Glycine max L. Merr.)

Rosenberg, L. A. and Rinne, R. W. 1986. Moisture loss as a prerequisitefor seedling growth in soybeanseeds (Glycine max L. Merr.).—J.exp. Bot. 37: 1663–1674. As soybean seeds [Glycine max (L.) Merr.] develop, they undergoa change in seed moisture. When excised prematurely from thepod and planted, seeds do not exhibit seedling growth until63 d after flowering (DAF) when the seed moisture has fallenbelow 60%. In contrast, seed germination (radicle protrusion)can occur when seeds as young as 35 DAF (68–79% moisture)are excised, but this germination docs not lead to comparableseedling growth frequencies unless seeds are first given a moistureloss treatment to artificially reduce their moisture below 60%.A moisture loss treatment applied at 35 DAF thus enables seedto undergo the transition from germination (cell expansion)to seedling growth (cell division and expansion) to the extentthat treated immature seed have a vigour index comparable toseeds matured on the plant (100%). The pattern of protein synthesisin vivo was examined in 35 DAF seed using [³⁵S]-methionine incorporation.When moisture loss treatment was applied for 24 h to 35 DAFseeds, seeds synthesized several new polypeptides when comparedwith untreated seeds at the same developmental stage. The sameseed samples showed 0% seedling growth in the absence of moistureloss treatment and 80% seedling growth when the treatment hadbeen applied. Moisture loss from soybean seeds appears to bea prerequisite for the synthesis of new proteins which may bepart of the metabolic process or processes that allow the soybeanseed to undergo the transition from seed germination to seedlinggrowth. Key words: Moisture loss, germination/growth, soybean     

SSR analysis of 38 genotypes of soybean (Glycine Max (L.) Merr.) genetic diversity in India

Sixteen polymorphic Simple sequence repeat (SSR) markers were used to determine the genetic diversity and varietal identification among 38 soybean (Glycine max (L.) Merr.) genotypes which are at present under seed multiplication chain in India. A total of 51 alleles with an average of 2.22 alleles per locus were detected. The polymorphic information content (PIC) among genotypes varied from 0.049 (Sat_243 and Satt337) to 0.526 (Satt431) with an average of 0.199. The pair wise genetic similarity between soybean varieties varied from 0.56 to 0.97 with an average of 0.761. These 16 SSR markers successfully distinguished 12 of the 38 soybean genotypes. These results suggest that used SSR markers are efficient for measuring genetic diversity and relatedness as well as identifying varieties of soybeans. Diverse genetic materials may be used for genetic improvements of soybean genotypes.     

Functional Correlation between Endogenous Phytohormone Levels and Hormone Autotrophy of Transformed and Habituated Soybean Cell Lines

We analysed the time course of the endogenous free IAA and cytokininlevels in hormone requiring and hormone autotrophic (both transformedand untransformed) Glycine max. L. Merr. cv. Mandarin tissuecultures. The auxin habituated line showed an enhanced endogenous IAAlevel, whereas the IAA as well as the cytokinin concentrationsin the cytokinin habituated line differed not significantlyfrom the non-habituated hormone requiring soybean callus. It were only the auxin habituated cells that could be inducedto fully habituated cells, from which a pale and a green typewas isolated. The phytohormone autotrophic growth of the paletype was sustained by enhanced IAA levels, whereas the greentype was characterised by elevated cytokinin concentrations. These results on the phytohormone content of partially and fullyhabituated soybean calli were compared with soybean crown galllines and discussed in view of the positive effect of exogenouslyapplied cytokinins on the endogenous IAA levels. ³Recipient of an Instituut voor Wetenschappelijk Onderzoek inNijverheid en Landbouw (I.W.O.N.L.) grant. ⁴Senior Research Associate Nationaal Fonds voor wetenschappelijkOnderzoek (N.F.W.O.). (Received March 25, 1988; Accepted July 7, 1988)     

Sugar Efflux from Attached Seed Coats of Glycine max (L.) Men.

Ellis, E. C. and Spanswick, R. M. 1987. Sugar efflux from attachedseed coats of Glycine max (L.) Merr.—J. exp. Bot. 38:1470—1483. Sugar efflux (sucrose + glucose) from attached seed coats ofGlycine max (L.) Merr. was measured at high sampling rates toimprove the kinetic characterization of seed coat exudation.This study confirms that sugar efflux in seed coats has at leasttwo components, and demonstrates that the concentration of mannitolosmoticum bathing the seed coat may influence one or both ofthese components. High leaf irradiance increased sugar effluxrelative to a low leaf irradiance at the same mannitol concentration.A high concentration of mannitol (500 mol m³) enhanced sugarefflux relative to a medium concentration (100 mol m³) underboth high and low leaf irradiance. A low mannitol concentration(10 mol m³) stimulated sugar efflux (relative to 100 mol m³)to a greater extent when leaf irradiance was high. Rapid changesin mannitol concentration produced immediate stimulations ofsugar efflux. Effects of osmoticum on sugar efflux are explainedby simultaneous turgor-mediated effects on import of sucroseby the phloem and retrieval of apoplastic sucrose, presumablyby seed coat parenchyma.     

Variation in the Durations of the Photoperiod-sensitive and Photoperiod-insensitive Phases of Post-first Flowering Development in Maturity Isolines of Soyabean [Glycine max(L.) Merrill] 'Clark'

Plants of eight isolines of soyabean [Glycine max(L.) Merrill],comprising all combinations of two alleles at the three lociE₁/e₁,E₂/e₂andE₃/e₃inthe cultivar ‘Clark’ background, were transferredafter different periods following first flowering from longdays (LD, 14 h d^-1) to short days (SD, 12 h d^-1) andvice versaina reciprocal-transfer experiment in a plastic house maintainedat 30/24 °C (day/night). Photoperiod (0.10>P>0.05),transfer time (P<0.001),>isoline (P<0.001), and theirinteractions (P<0.001) all affected flowering duration, i.e.the period from first flowering until the appearance of thelast flower. The flowering duration comprised two distinct phases:a photoperiod-sensitive phase beginning at first flowering,and a subsequent photoperiod-insensitive phase. The durationof the photoperiod-sensitive phase varied much more among theisolines in LD than in SD. Only the dominant alleleE₁increasedthe sensitivity of the photoperiod-sensitive phase of floweringduration to photoperiod singly, but positive epistatic effectswere detected betweenE₁andE₂,E₁andE₃, and especially among allthree dominant alleles. The increases in flowering durationresulting from the combined effects of gene and environment(i.e. photoperiod) were associated with considerable increasesin biomass and seed yield at harvest maturity.Copyright 1998Annals of Botany Company. Glycine max(L.) Merrill, soyabean, maturity genes, flowering, photoperiod, reciprocal transfer, yield.     

Soya Bean Seed Growth and Maturation In vitro without Pods

Immature Glycine max (L.) Merrill seeds, initially between 50and 450 mg f. wt, were grown and matured successfully in vitro.Excised seeds were floated in a liquid medium containing 5 percent sucrose, minerals and glutamine in flasks incubated at25 °C under 300 to 350 µE m^–2 s^–1 fluorescentlight. During 16 to 21 d in culture, seeds grew to a matured. wt of 100 to 600 mg per seed at an average rate of 5 to 25mg d. wt per seed d^–1 depending on initial size. Growthrates were maximal during the first 8 to 10 d in vitro but declinedwith loss of green colour in the cotyledons. Seed coats rupturedwith rapid cotyledon expansion during the first 2 d in culture.Embryos were tolerant to desiccation and 80 to 90 per cent germinatedif removed from culture before complete loss of green colour.The growth of excised seeds in vitro exceeded the growth ofseeds in detached pods, but when windows were cut in pods topermit direct exposure of seeds to the medium, seed growth wascomparable. Glycine max (L.) Merrill, soya bean, seed culture, seed growth, seed maturation, germination     

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.     

Protein Modification and Utilization of Starch in Soybean (Glycine max L. Merr.) Seed Maturation

Seeds of soybean (Glycine max L. Merr.) harvested at variousstages of development and allowed to dry in intact pods undergoa maturation process and are viable. Defatted powders of seedharvested 24–66 d after flowering were extracted to yieldbuffer-soluble and alkali-soluble proteins. Imposition of amaturation process increased the level of buffer-soluble proteinsbut had no effect on the disulflde content of these proteins.After undergoing maturation, seeds showed an accumulation ofbuffer-soluble polypeptides in the molecular weight range of43–94 kD. Maturation may be associated with the synthesisof specific polypeptides having a molecular weight of approximately85 kD. Alkali-soluble proteins, which represents the storageproteins, did not show any responses to maturation. Their quantityincreased substantially during seed development and the disulfidelevel was only half that of buffer-soluble proteins, attaininga maximum value of 10.9 mol S per 10⁵ g protein. Matured seedat all harvest dates had a final starch content close to thatof normal seed, 10–20 mg g^–1, and soluble sugarswere maintained at quite high levels, 51–83 mg g^–1.The metabolic program for synthesis and degradation of starchseems quite rigidly followed and is independent of harvest dateor of attachment to the parent plant. Soybean seeds retain considerablesoluble proteins and soluble sugars throughout maturation, andthese collectively may be important in maintaining a desiccationresistant structure.     

Morphological Description of Transgenic Soybean Chimeras Created by the Delivery, Integration and Expression of Foreign DNA Using Electric Discharge Particle Acceleration

Transgenic soybean (Glycine max L.) plants derived from electricdischarge particle acceleration experiments exhibited varyingdegrees of chimerism which was followed by the expression ofthe introduced ß-glucuronidase (gus) gene. Degreesof chimerism in transgenic plants were established by determiningexpression of the gus gene observed as blue spots, streaks orsectors in stem and leaf tissues in in vitro grown plantletsand greenhouse plants. Clonal plants were also obtained. Presenceof the gene was confirmed by Southern blot analysis. These studiespermitted the reconstruction of a partial picture for the developmentof the soybean plant. Glycine max L. cv. Williams 82, soybean, transformation, ß-glucuronidase, chimeric plant phenotypes, development     

Carbon Flow from Nodulated Roots to the Shoots of Soybean (Glycine max L. Merr.) Plants: An Estimation of the Contribution of Current Photosynthate to Ureides in the Xylem Stream

Kouchi, H. and Higuchi, T. 1988. Carbon flow from nodulatedroots to the shoots of soybean {Glycine max L. Merr.) plants:An estimation of the contribution of current photosynthate toureides in the xylem stream.–J. exp. Bot. 39: 1015–1023. Well-nodulated, water-cultured soybean plants were allowed toassimilate ¹³CO₂ at a constant specific activity for 10 h andthe ¹³C-labelling of total carbon and ureides in xylem sap wasinvestigated. Labelled carbon appeared very rapidly in the xylem stream. Percentageof labelled carbon (relative specific activity, RSA) in xylemsap was 18% at 2 h after the start of ¹³CO₂ assimilation andreached 53% at the end of the 10 h assimilation. The amountof labelled carbon exported from nodulated roots to the shootsvia the xylem during the 10 h labelling period accounted for33% of total labelled carbon imported into the nodulated roots.Ureides (allantoin and allantoic acid) in xylem sap were stronglydependent on currently assimilated carbon. The RSA of ureidesin xylem sap had reached 83% at the end of the assimilationperiod. Labelled carbon in ureides accounted for 51% of totallabelled carbon returned from nodulated roots to the shootsvia the xylem during the 10 h assimilation period. A treatmentwith 20 mol m^–3 nitrate in the culture medium for 2 ddecreased the ureide concentration in the xylem sap slightly,but greatly decreased the RSA of ureides. By comparing the data with the results of analysis of the xylemsap of nodule-detached plants, it was concluded that the majorityof labelled carbon exported to the xylem stream from noduleswas in ureide form. A considerable amount of carbon was alsoreturned from roots to shoots via the xylem stream but it wasmore dependent on (non-labelled) carbon reserved in the roottissues. Key words: Soybean(Glycine max L.), root nodule, carbon partitoning, ¹³CO₂ assimilation, xylem     

Characterization of the Photoperiodic Response of Post-flowering Development in Maturity Isolines of Soyabean [Glycine max(L.) Merrill] 'Clark'

Plants of all eight isolines of three maturity genes (all combinationsof two alleles at the three lociE₁/e₁,E₂/e₂,E₃/e₃) of soyabean[Glycine max(L.) Merrill] were grown in four different photoperiods(12, 13, 14 or 15 h d^-1) at 30/24 °C from first flower openingto harvest maturity. Photoperiod, isoline, and their interaction,affected significantly (P<0.01) the duration between firstand last flowering, and reproductive duration. The interactionsbetween genotype and photoperiod were sufficiently strong thatconsiderable differences in these durations were detected amongisolines in the least-inductive environment (15 h d^-1) whereasdifferences were negligible in the most-inductive regime (12h d^-1). There was a negative linear relation between photoperiodand both rate of progress from the appearance of the first tothe last flower, and rate of progress from first flowering toharvest maturity; sensitivity to photoperiod varied (P<0.05)six- and five-fold, respectively, among the extreme isolines(e₁e₂e₃andE₁E₂E₃). The three dominant allelesE₁,E₂andE₃, singly,had comparatively little effect on post-flowering traits, butconsiderable epistasis (particularly betweenE₁andE₂) was detectedfor sensitivity to photoperiod in respect of rates of progressfrom the appearance of the first to the last flower, and fromfirst flower to harvest maturity. Thus the large variationsdetected for these traits are the consequence of genexgene (xgene)xenvironmentinteractions.Copyright 1998 Annals of Botany Company. Glycine max(L.) Merrill, soyabean, maturity genes, flowering, photoperiod.     

Changes in Seed Constituents During Germination and Seedling Growth of Precociously Matured Soybean Seeds(Glycine max)

During 7 d of precocious maturation of soybean seed (Glycinemax), the starch content declined and soluble sugar levels increasedin patterns similar to natural seed dehydration and maturation.Total seed protein content and total seed dry weight increasedwhereas oil content remained relatively unchanged. Overall,the proportions of the constituents in precociously maturedseeds were comparable to naturally mature seeds. Precociouslymatured soybean seeds showed much the same germination and seedlinggrowth frequency patterns as naturally matured seeds. Duringgermination and seedling growth of precociously matured seeds,starch, soluble sugar, protein and oil levels followed patternssimilar to naturally mature, germinating seeds and seedlings.Therefore, precocious maturation may be used as a model systemto investigate the control of the physiological and biochemicalevents occurring during seed maturation which lead to germinationand subsequently, seedling growth. Glycine max (L.) Merr., soybean, cotyledons, maturation, germination/seedling growth