High Temperature Injury of Ripening in Rice Plant : V. On the barly decline of assimilate storing ability of grains at high temperature

Abstract

A jabonica rice (cv. Norin-17) was used to test the effects of high temperature treatment (day-night, 35-30°C) combined with the treatments which increase or decredse the available carbohydrate amount per grain, upon the ripening of rice grains. 1) Under high temperature, the rate of ripening was much higher at an early ripening period, but the inflow of assimilates into grain ended earlier (2 to 3 weeks after flowering), resulting in lower 1000-kernel weight than that of normal outdoor temperature. 2) At both high and normal temperatures, 1000-kernel weight was incredsed by thinning the panicle branches and was decreased by leaf-cutting or fertilizer dificiency. At high temperature, panicle thinning increasd 1000-kernel weight about 10%, while at normal temperature about 20%. 3) At both temperatures, the amount of TAC (total sugar plus crude starch) accumulated in each shoot was greatest at the no-treatment control, being fllowed in order by fertilizer deficiency, panicle-thinning and leaf-cutting. The total nitrogen accumulatlon was also greatest at the control, being followed by panicle-thinning, leaf-cutting and fertilizer deficiency. Panicl/Straw ratios in dry weight and in TAC amount at high temperature were lower than at normal temperature, indicating a relativelvy less TAC translocation into the panicle, leaving relatively more amount in the straw at high temperature. 4) An addition of CO2 to the ambient air combined with the above treatments did not increase the 1OOO-kernel weight at both temperatures indicating that CO2 amount was not limiting in this experiment. 5) The 1000-kernel weight did not increase at all after moving the plant from high to favorable temperatures if the plants had been treated at high temperature about 2 weeks after anthesis, whether the as-similate amount which should be stored in each grain was increased or decreased. (3) It was assumed that the main cause of early stoppage of maturation with a small 1OOO-kernel weight at hightemperature was an early decline of storing ability of assimilates in panicle rather than the decficiency of assimilate amount in the plant