POST-HEADING PRODUCTION AND DISTRIBUTION OF ASSIMILATES IN RICE PLANTS AS INFLUENCED BY SINK MANIPULATION

The prupose of this study was to investigate the post-heading assimila tion and distribution of carbohydrate and nitrogen in rice plants as i nfluenced by reduced sink demand through spikelet removal or male ster ility. Field experiments were conducted in the 2nd crop of 1987 and 1s t crop of 1988 by using cultivars Tainung No. 67 (TNG(67)) and Taichun g Sen No. 2 (TCS2) and their cytoplasmic male sterile near-isogenic li nes (TNG(67)A and TCS(2)A) as materials. TNG 67 was also cultured in p addy tanks in the 2nd crop of 1989 to study the effect of panicle clip ping on photosynthesis of the source leaves. Experimental results reve aled that the reduction of panicle sink, either by male sterility or s pikelet clipping, showed no significant effects on the photosynthesis of the uppermost two leaves. The total N content remained relatively s table or decreased during the course of grain-filling in both the fert ile and sterile plants. No significant difference in total N content w as observed between the fertile and sterile plants. Both the fertile a nd sterile plants accumulated total nonstructural carbohydrates (TNC) at about the same rate during the first two weeks after heading. Howev er, the accumulation of TNC ceased in the sterile plants thereafter be cause of the vigorous growth of the young tillers emerged after headin g. The developing grains were the majors sink in the fertile plants, w hereas stem, leaf sheath and the newly-emerged young tillers were the alternative sinks in the plants with either male sterility or spikelet -clipping. It was concluded that under the current experimental condit ions, reduction in sink demand of rice plants could induce a drastic c hange in the pattern of assimilate partitioning rather than the inhibi tion of assimilate production.