水稲幼植物の低温障害に関する研究 : 第3報 低温による葉身葉緑体の微細構造の変化とその品種間差異

抄録

Electron microscopic observations were made on the ultrastructural changes of the chloroplasts of leaf-blade mesophyll cells in the 3rd leaf which was fully expanded and the 5th leaf which was developing at the start of temperature treatments. The temperature treatments were started at 3.2 to 3.3 leaf number stage. The varieties used were Sasanishiki (japonica), IR 24 (indica) and Milyang No. 23 (japonica×indica). 1. Under normal temperature (25°/20°C), the leaf color of the 5th leaf was white when it was 3 to 4 mm length, yellowish white when it elongated to 2 to 3 cm length, and green when it emerged 4 to 5 cm above the 4th leaf sheath. The plastids of mesophyll cells developed from proplastids to chloroplasts along with greening of the leaf, and with increasing of their grana and thylakoid stratum resulted from fusion of vesicles (Fi9. 1-7). 2. Under low temperature (17°/12°C) for 2 weeks, the greening of the 5th leaf was suppressed; the leaf color of Sasanishiki became light green, and yellowish in those of Milyang No. 23 and IR 24. The Chloroplasts of Sasanishiki contained large starch grains and a considerable number of grana, but those of Milyang No. 23 and IR 24 contained small starch grains and numerous vesicles without forming normal grana (Fig. 8-10). The 5th leaf grown under 1 week normal temperature after 2 weeks low temperature pretreatment, restored its color to green. The chloroplasts of mesophyll cells in all varieties rapidly restored grana formation, degrees of the restoration being higher in Sasanishiki, Milyang No. 23 and IR 24 in that order (Fig. 11-13). 3. Under low temperature for 1 or 2 weeks, the 3rd leaf discolored; light green in Sasanishiki, yellow or brown in Milyang No. 23 and IR 24. Under low temperature for 1 week, the chloroplasts of mesophyll cells in all varieties contained large starch granis and limited number of grana-thylakoids (Fig. l7-19). After 2 weeks of low temperature, the chloroplasts in Milyang No. 23 and IR 24 contained macrograna, but no starch grains, and decreased number of grana. Single thylakoids arranged parallel with the chloroplast envelope were often observed (Fig. 20-23). The chloroplasts of the subepidermal cells of the adaxial surface contained numerous vesicles which might be formed from separated thylakoids (Fig. 24, 25). The chloroplasts of mesophyll cells only in IR 24 contained phytoferritin in stroma (Fig. 23). 4. The subepidermal cells of the adaxial surface of the 3rd leaf in Milyang No. 23 and IR 24, which became brown due to low temperature for 1 or 2 weeks, formed dehydrated masses which contained large starch grains. The chloroplast envelope became indistinguishable (Fig. 26, 27).