Post-heading production and distribution of assimilates in rice plants as influenced by sink manipulation

Abstract

The prupose of this study was to investigate the post-heading assimilation and distribution of carbohydrate and nitrogen in rice plants as influenced by reduced sink demand through spikelet removal or male sterility. Field experiments were conducted in the 2nd crop of 1987 and 1st crop of 1988 by using cultivars Tainung No. 67 (TNG(67)) and Taichung Sen No. 2 (TCS2) and their cytoplasmic male sterile near-isogenic lines (TNG(67)A and TCS(2)A) as materials. TNG 67 was also cultured in paddy tanks in the 2nd crop of 1989 to study the effect of panicle clipping on photosynthesis of the source leaves. Experimental results revealed that the reduction of panicle sink, either by male sterility or spikelet clipping, showed no significant effects on the photosynthesis of the uppermost two leaves. The total N content remained relatively stable or decreased during the course of grain-filling in both the fertile and sterile plants. No significant difference in total N content was observed between the fertile and sterile plants. Both the fertile and sterile plants accumulated total nonstructural carbohydrates (TNC) at about the same rate during the first two weeks after heading. However, the accumulation of TNC ceased in the sterile plants thereafter because of the vigorous growth of the young tillers emerged after heading. The developing grains were the majors sink in the fertile plants, whereas 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 conditions, reduction in sink demand of rice plants could induce a drastic change in the pattern of assimilate partitioning rather than the inhibition of assimilate production.