Studies on the Development of Endosperm in Rice : 6. Effects of early-season cultural practice on the size of endosperm and the number of cell layers of endosperm.

Abstract

In case of early-season cultivation, the ripening period was moved up to warmer season by about 30 days earlier than in the case of ordinary-season culture, and the daily mean temperature at the ripening stage in the early cultural season was by 2°C higher than that of the ordinary cultural season. The experimental results obtained from the test for 4 Japonica varieties are summarized as follows: Length of the longitudinal diameter of endosperm obtained from early-season cultivation was slightly shorter than that of endosperm under the ordinary-season cultivation. While, it showed no difference in the number of cell layers of endosperm grown under the two cultural conditions. As to the dorsal radius of endosperm, the size and number of cell layers of endosperm grown in early-season were almost similar to those of endosperm grown in the ordinary-season. However, the number of starch cell layers showed somewhat decrease e in case of early-season cultivation from that in case of the ordinary-season culture owing to the increase of aleuron cell layers. The most remarkable differences were observed on the ventral radius. Comparing with the ordinary-season cultivation, early-season cultivation showed 6.0 to 22.5% decrease in length and a 8.7% decrease on an average in the number of cell layers, respectively. No significant differences were found in the lateral radius of endosperm according to the different cultural seasons. It seemed that the number of cell layers might be more invariable than the length, in other words, the cell division is less affected adversely by the enviromental conditions in the ripening stage than the elongation of the cells. The ratio of dorsal radius to ventral radius of endosperm grown in the early-season was larger than that of endosperm grown in ordinary-season. The ratio of breadth (sum of the dorsal radius and ventral radius) to thickness (twofold of the lateral radius) of endosperm gorwn in early season was less than that of endosperm grown in the ordinary-season. Namely, the shape of endosperm developed under the early-season cultural condition showed shorter and more roundish than that developed under the ordinary-season cultural condition.