Ecophysiological Factors In Influencing Seed Size Of Soybean(Glycine Max (L.) Merrill)

In order to examine the relationship between soybean seed growth, cotyledon cell number, cell growth rate, cell volume with plant endogenous hormone concentrations, as well as the exogenous hormone effect on single seed size and the accumulation of assimilate, seed fatty acids and protein, three semi-determinate soybean varieties differing in quality and 100-seed weight were planted with three planting densities in the field of Hailun Agroecological Experimental Station, Chinese Academy of Sciences from 2007-2008.. The three varieties are Hai 339(H339), big seed size; Heinong 35 (HN35), medium seed size with high-protein content; Kennong 18(KN18), small seed size with high fat content.During seed filling, big seed variety had higher dry matter accumulation rate. The rate of seed filling was positively correlated to cotyledon cell number. More cotyledon cell number, greater cotyledon cell volume and cell weight was found in big seed size variety, while medium and small seed size varieties had less cotyledon cell number, lower volume and cell weight. Big seed size variety owned higher ratio of seed and pod wall. Higher ratio of seed and pod wall was an indicator of assimilate transportation between seed and pod wall, and thus was extremely beneficial to seed filling and improvement of harvest index.The dynamic of seed ABA concentration was significantly correlated to seed growth rate. The ABA concentration in big seed variety was constantly higher during seed filling than that of the medium and small varieties, especially in the second half of the seed filling. Correlation coefficient (P<0.05)was 0.92**in HN35, while H339 and KN18 was 0.85**,0.83** respectively.In the big seed size variety, significant correlation between dynamic of GA3 concentration and seed growth rate was also observed(r=0.87**), while for the medium seed size variety, the relationship between GA3 concentration and seed growth rate was not closely related(r=0.63*) .No close relation was found between ZR concentration and seed growth rate. The ZR concentration present a single peak in H339 and KN18, which occurred at 40 days after flowering, while the ZR concentration in HN35 remained relatively stable. It is proposed that soybean seed quality might be related with the dynamic of ZR concentration.Enriched light treatment at the early pod-setting. stage increased seed yield. The yield increase was mainly attributed to the increase in 100-seed weight. For the big seed size variety, the increase in seed size by light enrichment was due to the increase in cotyledon cell volume and cell weight, but primarily due to cell number increase for the medium and small seed variety.In seed development, the regulation of potential sink to light availability is through cotyledon cell number and seed growth rate. For the big seed variety, 100-seed wight was greatest in the highest density. The spatial distribution of single seed-weight in the main stem was"┃"shaped, and planting densities had weak effect on the soybean single seed, but different responses existed among varieties to differnet planting density. Single weight of the small seed variety had higher stability compared with the least unstability in the big seed variety.The big seed variety had the greatest concentration of linoleic,linolenic and stearic acids followed by the medium, and the small seed variety had the least. However, the small seed variety had the greatest concentration of palmitic acids and oleic acids, followed by the medium, while the big seed variety had the least. The concentration of linoleic acids increased gradually with seed filling in big seed variety. In the late seed filling, the concentration of linoleic acids increased significantly.Different soybean varieties had significant difference in seed relative protein concentration. The greatest relative protein in big seed variety and greatest fat, content in small seed variety was observed 30 days after flowering, In the seed filling, the small seed variety had the most relative soluble sugar content, which may be due to lower translocation rate On opposite, the big seed variety had higher rate of translocation resulting in a lower relative soluble sugar content. Although the small seed variety had higher relative soluble sugar content compared with the big seed variety, the absolute soluble sugar content was greater in big seed variety than that of small seed variety.The results of the study provids a scientific basis for exploreing the realitionship between seed development, hormone signal, assimilate accumulation and cotyledon cell traits, it also provides a reference for evaluating high-yield variety and breeding germplasm resources. Hormone activities in relation to quality in soybean seeds need further study.