Studies on Structure and Function of the Rice Ear : I. Fixation of 14C by ear and shoot, and redistribution of 14C-assimilates among organs

[摘要] The main aims of the present investigations are (1) to determine the assimilation rates of 14CO2 of the organs consisting the rice ear, i.e. hulled grain, hull, abortive grain and rachis-branch (including rachis and pedicel), and then (2) to determine the redistribution of 14C-assimilates among those organs after a given time. Plants from 10 to 14 days after ear emergence were used through the present experiments. 14CO2 gas was applied to the materials in following two ways; one is to the ear, and another to the shoot. The materials were harvested immediately after one hour exposure to 14CO2 for (1) experiment and at one week after exposure to 14CO2 gas for (2) experiment. When 14CO2 gas was applied to the ear, assimilation rates of 14CO2, i.e. 14C/mg dry weight/hr and 14C/1OO spikelets/hr were high in the rachis-branch, while were very low and/or almost negligible in the hulled grain and the hull. The translocation rate of 14C-assimilates to the hulled grain was most rapid for one hour following one hour exposure to 14CO2 gas, and became slow thereafter. The translocation of 14C-assimilates to the hulled grain, however, seems to continue for five to seven hours after exposure to 14CO2 gas. For one week following exposure to 14CO2 gas, the hulled grain functioned as a greedy "sink" organ of 14C-assimilates, while the rachis-branch and the abortive grain as a rich and a poor "source" orga'n of 14C-assimilates, respectively. On the other hand, the hull worked as a "source" organ in some cases, but in others. Each of "sink" and "source" capacities of the hull, however, was very small compared to the hulled grain and the rachis-branch. The assimilation rate of 14CO2 of the rachis-branch, 14C/100 spikelets/hr tended to be higher in varieties which was heavier in dry weight of the rachis-branch per 100 spikelets. Tsuno, et al. (1975) showed that net ear photosynthesis correlated positively with chlorophyll content of the ear. Therefore, the basic benefit of heavy dry weight of the rachis-branch may be to associate with the dense thickness and the anatomy having relatively high proportion of photosynthetic components. It is interesting that the varieties showing high assimilation rate of 14C/ 100 spike1ets/hr tended to be also high in 14C/mg dry weight/hr. When 14CO2 gas was applied to the shoot, the assimilation rates of 14CO2 of leaf blade and sheath were the highest in flag leaf. The assimilation rate of 14CO2 of the rachis-branch, 14C/mg dry weight/hr was similar to it of the flag leaf sheath and from one-half to one fourth of the flag leaf blade. The rachis-branch worked as only one "source" organ of 14C-assimilates in the ear, while others as "sink" organs. The proportion fixed by the ear out of the total amount of 14C-assimilates, however, was 4%, and it fixed by the rachis-branch 3%.

[学科分类] 农业科学（综合）