High Temperature Injury of Ripening in Rice Plant VI. Enzyme activities of kernel as influenced by high temperature

Abstract

To clarify the cause of early clecline of assimilate storing ability of grains by high temperature during ripening period, enzyme activities of kernels which may be concerned with the ability was compared at high and normal temperature with the progress of maturation. 1) Respiration rate of kernels declined with the prbgress of ripening, more rapidly at high temperature reachihg the lowest level at two weeks afrer anthesis. Oxygen uptake by kernel mitochondria followed a similar pattern as kernel respiration and ADP/O ratio at high temperature reached zero at thh 14th day, whereas that at normal temperature remained fairly high until maturity. When ADP/0 radio at high temperature rapidly declined, available starch still femained in the straw although of small amount. Water percentages of kernels rapidly and that of leaf-blade gradually decreased with the progress of ripening, being always lower at high temperature. 2) Carbohydrate and nitrogen contents of kernels paralleled with 1000-kernel weight during ripening at both temperatures, but protein-N at high temperature stopped to increase before the 14th day of treatment and non-protein-N gradually incrcased thereafter. 3) Phosphorylas activityj reached a maximum at the 1Oth day and theh gradually decreased at both temperatures, being lower at high temperature. 4) Yellowing of spikelet was first recognized At rachilla portion and occurred earlier at high temperature Succinic-dehydrogenase activity at rachilla disappeared at the 16th day and soon yellowing started. Kernel enzyme activities seemed to declin earlier than disappearance of succinic-dehydrogenase activity at rachilla. 5) It was suggested that the early decline of assimilate storing ability of grains at high temperature had a close relation to early decline of physiological activities of kernel cells