The Growth Responses of Soybean Plant to Photoperiod and Temperature : VI. Starch accumulation and chloroplast fine structure in soybean leaf as affected by temperature

Abstract

The soybean plants (cv. Miyagishirome) were grown in the phytotrons under natural light at day/night temperatures of 30°/25°, 24°/19°, 17°/12° and 9°/9°C. The 6th trifoliate leaf (numbered from the base) which was fully expanded at the start of temperature treatment was sampled two times at weekly intervals during the treatment, and the young developing 11th leaf which was ca 0.5 cm long at the start was sampled three times: at the time when it elongated 1.0-1.5 cm long, when it elongated ca. 3.0 cm long, and fully expanded at respective temperature treatment. The samples were embedded in spurr resin and observed under both light- and electron microscopes. The results are summarized as follows: 1. Starch accumulation in the 6th leaf plastids was most abundant at 17°/l2°C'and decreased in the order of 24°/19°, 9°/9° and 30°/25°C, showing a tendancy to deposit most in the 2nd layer of palisade mesophyll and then at the inner layer of spongy mesophyll (Figs. 1-4). 2. The 11th leaf at the start consisted of six cell layers except around the vascular bundles (Fig. 5). When it elongated to ca 3.0 cm. long, the paraveinal cells began to expand and vacuolate ahead of the palisade and spongy cells (Figs. 9, 10), and at this time chloroplasts were scattered in the cytoplasm. In the fully expanded 11th leaf the starch accumulation under each temperature was almost similar to that of the 6th leaf (Figs. 11-13). 3. In the 11th leaf, starch accumulated most abundantly at 17°/12°C during all its developmental phases. It was observed that epidermal cells including trichomes and subepidermal mesophyll cells contained more starch granules than the inner cells when it was 1.0-1.5 cm long, but the cells of all layers contained them rather uniformely when it elongated to ca 3.0 cm long (Figs. 6, 9). When it fully expanded, starch granules disappeared in the epidermal and paraveinal cells, and thereafter new starch granules accumulated in all the mesophyll cells except vascular bundles. 4. The fine structure of chloroplasts of the 6th leaf was little affected by 17°/12°C, while at 9°/9°C after one week treatment an abnormal swelling of thylakoids and many vesicles appeared in the chloroplast, the tendency becoming more clear after two weeks. (Figs. 14-16, 21-23). The 11th leaf didn't expand after 3 days of treatment at 9°/9°C and its chloroplasts remained without development, although those at the other treatments formed thylakoid and grana faster the higher the temperature. 5. Starch accumulation in the chloroplast seemed to be more abundant during daytime than during nighttime (Figs. 24, 25 and Table 1).