Changes of Fine Structure of Soybean Cotyledons During Seed Ripening, Germination and Emergence

Abstract

Two observations were made. Firstly, growth and fine structures of cotyledons of ripening soybean seeds under high and normal temperatures were compared under light microscopy and electron microscopy. Secondly, changes of fine structure of cotyledons during germination, emergence and yellowing were observed. Soybean used is cv. Miyagishirome. The mean day/night temperatures were 35°/30°C (high temperature) and 24°/19°C (normal temperature). The results obtained are summarized as follows: 1. The seed maturity at 24°/19°C was about three weeks faster and 100-seed weight was greater than those at 35°/30°C. The number of seeds ripened per plant was almost the same between the two on account of very high sterility at 35°/30°C, although the number of pods per plant was greater at 35°/30°C (Tables 1 and 2). 2. The number of cell layers in both lengh and width directions of cotyledon was greater at 24°/19°C than at 35°/30°C, but that in thickness in opposite. The mean cell length of matured cotyledon was greater at 24°/19°C than at 35°/30°C, but the mean diameter was smaller at 24°/19°C (Tables 4 and 5). 3. Carbohydrate concentration (sugar+starch) was higher at 24°/19°C than at 35°/30°C, but protein concentration in opposite (Table 3). 4. The number of starch granules was most abundant in late ripening periods (Sep. 27 at 24°/19°C and Oct. 16 at 35°/30°C. At maturity they were almost disappeared from all parts at 35°/30°C and from abaxial parts at 24°/19°C. A few thylakoids appeared among starch grains during ripening period. Protein body was small at early ripening period, then became amoeba like at middle and late ripening periods, and grew up to bigger, round bodies at maturity. Mary endoplasmic reticulums were observed in adaxial parts of the cotyledon at middle and late ripening periods. Lipid spherical bodies were packed reticulately among the protein bodies just before maturity (Figs. 1-32). 5. The partitioned protein granules appeared in parenchyma cells of the cotyledon germinated but remained in the soil, and lipid bodies were almost disappeared at this time. In completely emerged yet folded cotyledon, thylakoid formation and starch deposition preceeded at abaxial part, but after unfolding they became more prominent at adaxial part, suggesting a light reception be concerned (Figs. 33-35). When cotyledon turned yellow, thylakoids were separated to form numerous vesicles (Fig. 36). These procedures seemed to proceed faster in abaxial parts.