Relationship between the Grain Weight and Ammonium Concentration in the Rice Grain of Restrained Ripening

[摘要] Rice plants grown in pots were given a few treatments in order to restrain its ripening. Morphological characteristics and physiological factors relating to grain weight were investigated. Throughout all treatments, the dry 1000 grain weight at matured time had a highly positive correlation with the raw 1000 grain weight at around 17 days after full heading date. It seems that the matured grain weight was strongly regulated by the volume of young grain at the milky stage. Increasing rate of grain weight during the milky stage was depressed by night temperatures of 5°C lower and 8°C higher than in the outdoor. However, photosynthetic activity and carbohydrate accumulation in the stem and sheath were not so much influenced by both temperatures at night. Two treatments, the temperature 5°C higher than outdoor given to the ear and the solutions of 1000 ppm Asparagine and 20 ppm KNO3 respectively supplied through a part of the peduncle, were applied throughout the ripening period. The grain weight was significantly reduced in both treatments compared with that of controls. There was found a negative correlation between the ammonium concentration of the matured brown rice and its weight. The brown rice of low sugar concentration showed a lower ammonium concentration and a higher increasing rate of grain weight. These results suggest that starch synthesis in the rice grain is inhibited by high ammonium concentration which is increases due to accumulation of total amino acids evolved by disorder of protein metabolism.

[学科分类] 农业科学（综合）

[关键词] Amino acid;アミノ酸;Ammonium concentration;アンモニア濃度;Grain weight;水稲;Protein metabolism;窒素代謝;Rice plant;デンプン合成;Sugar concentration;登熟不良;Starch synthesis;糖濃度;粒重