On the Low Temperature Damage in Rice Seedling : II. Varietal difference in discoloration of leaves under low temperature and their restoration to green when moved to normal temperature, with respect to change in pigment compositions

Abstract

This study was done in phytotoron under natural light to clarify the processes of discoloration of rice leaves under low tenperature (17°/12°C), and their restoration to green under normal temperature (25°/20°C) switched from low temperature pretreatment, with respect to chlorophyll content and pigment compositions. Results obtained are summarized as follows: 1. The yellowing degree of leaf blades by low temperature coincided with the detree of decrease in chlorophyll content, being highest in IR 24 and lowest in Sasanishiki. The chlorophyll content of leaf blades at the 7th day under normal tenperature after low temperature pretreatment for a week increased more than that grown for 2 weeks under normal tempreature. The degree of increase was Sasanishiki > Milyang No. 23 > IR 24 in order. 2. The heights of absorption peaks of ethyl estracts of yellowing leaf blades under low temperature decreased compared with those of green leaves under normal temperature. The degree of decrease was IR 24 > MIlyang No. 23 > Sasanishiki in order. The maximal absorbance at the red (657 nm) and blue (432, 451 nm) bands under low temperature decreased compared with those under normal temperature, and that at the red band decreased more than at the blue band. 3. The heights of absorption peaks of ethyl ether extracts of greening leaf blades at the 7th day under normal temperature after a week of low temperature pretreatment increased than those under normal temperature for 2 weeks. The degree of increase was Sasanishiki > Milyang No. 23 > IR 24 in order. The rate of increase at the red band was greater than that at the blue band. 4. By low temperature treatment, the relative amount of the yellowish pigments increased more than that of the greenish pigments, and the rate of increase of the former pigments was IR 24 > Milyang No. 23 > Sasanishiki in order. The acetone-and water-soluble pigments (anthocyanin) increased under Iow temperature treatment and the degree of increase was IR 24 > Milyang No. 23 > Sasanishiki in order. 5. It was suggested that the yellowing of rice leaves by low temperature was caused by a decrease of chlorophyll content and by an increase in the ratio of yellowish/greenish pigments in amount, although the contents of both pigments decreased by low temperature. The order of yellowing of leaf color under low temperature was coincided with the order of decrease in chlorophyll content and increase in yellowish/greenish Pigments.