Studies on the Ripening of Wheat Grain : 4. Influence of temperature upon the development of the endosperm

From the date of flowering to the full ripening stage, the developmental processes were studied at natural, 20°C and 30°C constant conditions. At 20°C, in comparison with the natural condition, the rate of development was same in Stages I-IV (from the division of endosperm mother nucleus to the stage of the peripheral cell layer formation), slightly quicker in Stages V-XI (from the stage of filling up of the embryosac cavity with endosperm cells to the stage of beginning of cell maturation) and was very slow in the last Stages XII-XIII (completion of cell growth and constriction of tissue). At 30°C, the developmental processes were hastened by 1.5∼2 times than that at 20°C, and finally reached the last Stage XIII on the 23rd day after anthesis. Among three temperature conditions, there were no differences in the number of endosperm cells. Hence, it may be said that the division of the endosperm cells, that is, the increase of the cells in number is independent of the temperature. However, at high temperature, the growth of the cells were hindered and the cells were smaller in size though they matured. At 30°C, the reserve starch grains began to deposit in the endosperm cells about 2∼3 days earlier than in the case of 20°C and of the natural condition. But at 30°C, the first type of starch grains found to be slightly smaller in size, and that the second type of starch grains appeared to be remarkably scantier in number than in the case of natural condition. There were no remarkable differences in the development of the starch grains between 20°C and natural condition. The above observations indicate that the temperature has a influence on the maturation of the endosperm cells, and that especially high temperature shortens the time in the ripening stages. Besides, the high temperature hastens the withering of the assimilate organs, and all leaves were already withering up in 19 days after anthesis at 30°C. Therefore, it may bring the decrease of the reserve substances which were supposed to be transported into the ear. Consequently, the seeds riped at 30°C were very thin in shape and light in weight. It was an interesting fact that the temperature affected not only the grain weight, size, color and protein content, but also the shape of the endosperm cells and size and number of the starch gains which were closely related to the quality of the flour and its taste.