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     

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     

Plant regulated aspects of nodulation and N2 fixation

Abstract. Root nodule organogenesis is described. Plant regulated aspects of nodulation and N₂ fixation are reviewed and discussed. Since the effective N₂ fixing symbiosis requires the interaction of the host plant and bacterium in an appropriate environment (the rhizosphere and the root nodule) it is essential that research aimed at improving N₂ fixation involve a knowledge and understanding of the plant genes that affect nodule development, growth, and function. Current knowledge of host plant genes involved in N₂ fixation is summarized. Various experimental approaches to the study of the host plant's contribution to nodulation are noted. The functions of nodule specific proteins (nodulins) in symbiosis are delineated. Future areas of research are suggested.     

The Effect of Source-Sink Alterations on Soybean Seed Growth

Soybeans (Glycine max L. Merrill) were grown in the greenhouseand in the field to investigate the effect of variations inthe assimilate supply during the linear phase of seed developmenton the rate and duration of growth of individual seeds. Increasedassimilate supplies, created by partial fruit removal, increasedrates of dry matter accumulation, duration of seed growth, andfinal seed size (weight per seed). Reductions in the supplyof assimilate to the developing seed, created by shading (60per cent) the plants during the linear phase of seed development,lowered seed growth rate but did not affect final seed sizebecause of a longer duration of seed growth. Nitrogen stressduring seed development, created by removing N from the nutrientmedium, did not affect seed growth rate but shortened the durationof seed growth and reduced final seed size. The data indicatethat the growth characteristics of soybean seed are influencedby the supply of assimilate to the seed during the linear phaseof seed development. Glycine max L., soybean, seed growth rate, duration of seed growth, effective filling period     

The Effect of Population Density on Floret Initiation, Development and Abortion in Winter Wheat

There is little information in the literature concerning thephysiological basis of the relationship between plant populationdensity and kernel number in winter wheat (Triticum aestivumL.). Thus, two experiments were conducted to evaluate this relationship.Expt 1, involving three population densities, was carried outnear Taian, China in 1982 and in Expt 2, two densities wereevaluated near Lexington, Kentucky in 1986. Plants were sampled every 2 d in the spring, main stem spikeswere dissected and florets were scored according to a 10-stagescale of development. The rate of primordia initiation increasedas density increased until the point at which primordia numberswere equal in all treatments. After this point, an increasein density reduced the primordia initiation rate. In both experimentsincreasing density reduced the total number of floret primordiainitiated and the number of kernels per spike. In Expt 1 theeffect of density on kernel number per spike was accounted forapproximately equally by the effect of density on number ofprimordia initiated and floret abortion. In Expt 2, however,floret abortion was influenced much less by density and accountedfor only 7 % of the variation in kernel number per spike. Thekey result was that the effect of density was determined earlyin floral development. The data suggest that yield losses athigh densities may be determined too early in development tobe offset by N applications at the terminal spikelet stage. Triticum aestivum L., spike development, spikelet development, seeding rate