CARBOHYDRATE-METABOLISM IN LEAF BLADES AN D STEMS OF RICE CULTIVAR AKITAKOMACHI AT THE RIPENING STAGE

Akitakomachi was cultivated in a paddy field, and the lower leaves and about 1/3 of an ear were clipped off before and immediately after hea ding, respectively. The effect of the treatments on the carbohydrate m etabolism in the leaf blades and stems including leaf sheathes at the ripening stage was analyzed. The leaf blades accumulated the photosynt hate mainly as sucrose but a little as starch. With the increase of ca rbohydrate content in the leaf blades, the ratio of sucrose in the car bohydrate increased. The accumulation of carbohydrate in the stems was principally similar to that in the leaf blades except that st-arch la rgely accumulated when a large accumulation of carbohydrate occurred. At early ripening stage with a vigorous increase of ear weight, the co ntent of carbohydrate, especially sucrose, decreased in the leaf blade s and more remarkably in the stems. At middle to late ripening stage, the rate of increase in ear weight gradually decreased. After ear weig ht reached its maximum, photosynthate began to reaccumulate in the lea f blades and stems; especially, the accumulation of sucrose was remark able. The activity of sucrose phosphate synthetase in the flag leaves at the ripening stage gradually decreased as leaf senescence proceeded .