Studies on Structure and Function of the Rice Ear : II. Photosynthetic and respiratory activities of organs consisting the rice ear

[摘要] Relations of photosynthetic and respiratory activities of rachis-branch including rachis and pedicel, husk and hulled grain with their nitrogen content were examined. The age of ear used for measurements was the same as in a previous report (SASAHARA, 1981). Changes in ear respiration with ear temperature were determined on four indica, three japonica and four large grain varieties. Ear temperature increased at the rate of 2 or greater for a temperature coefficient, 〓10 in the range of ear tempcrature from 20 to 30°C, but became smaller than 2 for 〓10 in some varieties above 30°C of ear temperature. The different response of ear respiration to the high ear temperature seems due to varietal difference in ear physiology. Both the increasing rate of car respiration and its value at the different ear tempcrature showed some varietal variations. Measurements of ear photosynthesis and respiration on 23 cultivars were made in about 50 days from August 6 for an extremely early maturing variety, Ishikarishiroge to September 21 for an extemely late maturing one, Yamahoshi. During the measurement period, outdoor temperature changed and influenced ear temperature in an assimilation chamber irradiated, changed 33 to 40°C on an average, but in darkness was kept at 19°C. Temperature of the ingoing air at the entrance of an assimilation chamber correlated negatively with the temperature difference between temperature of the ingoing air and ear temperature in an irradiated chamber, while the temperature difference correlated positively with ear temperature. Thus, the high temperature difference seems to have been caused by the low temperature of ingoing air and the high temperature of ears due to exposure to the former, i.e. ears of some varieties incrcased its temperature against the low temperature of ingoing air. Such increase of ear temperature seems to reflect changes in some physiological activities of ear with transfer from the outdoor of low temperature to the warm condition irradiated. Each of the temperature difference, temperature of the ingoing air and ear temperature, however, showed no significant correlation at least with net ear photosynthesis. Therefore, those three temperature factors appears to have no effect on varietal difference of net ear photosynthesis. Nitrogen content of the rachis-branch including rachis and pedicel correlated positively with net ear photosynthesis and ear respiration (r=0.477 and 0.449, respectively, and each is significant at 5% level). Nitrogen content of the husk showed no significant correlation with net ear photosynthesis, but positively with ear respiration (r=0.447, significant at 5% level). Nitrogen content of the hulled grain showed no correlation with net ear photosynthesis and ear respiration. In the previous report (SASAHARA, 1981), the rachis-branch was regarded as one of the most important organs in ear photosynthesis, i.e. almost all 14C-assimilates in the rice ear were fixed by the rachis-branch and negligiblely by the husk and the hulled grain. The present results coincide well with the previous report. Besides, the correlation of nitrogen content of the rachis-branch to ear respiration may show that the rachis-branch functioned actively for translocation of the assimilates from other organs to the ear, and it is interesting that nitrogen content of the husk showed a correlation with ear respiration. In case of the hulled grain, the storage protcin in the grain might have obscured the fraction active for respiration.

[学科分类] 农业科学（综合）