Abstract
Rice plants, the variety Norin No. 29, were ripened after flowering in glassrooms, controlled at constant temperatures of 17°C, 21°C and 25°C respectively, and the behaviour of carbohydrates and its related enzyme activities were studied. Samples were taken at intervals of 4 days from flowering. Each of these samples was divided into the ear and the 1st, the 3 rd and the 5 th internodes respectively from the panicle downwards. The distribution and rise or fall in the contents of sugar, starch, and some enzymes (amylase, phosphorylase, invertase, and hexokinase) which were related to the metabolism of carbohydrate, respectively were determined. The activity of those four enzymes in respect of each part of the plant, which ripened at the low temperature, was not so much low. On the 65th day after flowering, the dry weight and the starch content of the ear were respectively highest at 21°C and were almost equal between 25°C and 17°C. But the process of ripening at 25°C and that at 17°C were quite different from each other. At 25°C, the dry weight and the starch content of the ear increased rapidly and then ceased accumulating at an early stage of ripening. On the contrary, at 17°C it increased slowly but steadily and it continued until the 75 th day after flowering. Sugar and starch in the culm were translocated to the ear at an early stage in the treatments of 21°C and 25°C, but not in that of 17°C. The following conclusions were drawn from the above mentioned results. The impediment in ripening at high temperatures is mainly due to the cessation of ability of the ear as a "receiving organ" at an early stage, and at low temperatures it is mainly due to the disturbance in supply of materials to the ear from the culm.
