POST-HEADING PARTITIONING DYNAMICS OF TOT AL NONSTRUCTURAL CARBOHYDRATES IN RICE PLANTS AS INFLUENCED BY SINK MANIPULATION

Results from previous experiments indicated that in rice, reduction of sink demand resulted in no remarkable change in photosynthesis or tot al dry matter production, however, significant accumulation of carbohy drates and N in the vegetative organs was observed. It therefore sugge sted that post-heading sink manipulation could lead to a drastic shift in the pattern of assimilation distribution rather than a decrease in assimilate production. The purpose of this study was to investigate t he partitioning dynamics of total nonstructural carbohydrates (TNC) am ong leaf blade, leaf sheath, and stem at different node positions of r ice plants subjected to sink manipulation by spikelet removal or male sterility. Experimental results revealed that, as compared to fertile plants, sink manipulation increased TNC concentrations in the leaf bla de, leaf sheath, and stems during the grain-filling period. The increa se of TNC concentration in the stem internode was especially significa nt. Concentrations as high as 55-58% were recorded in the 3rd and 4th internodes (counted basipetally) between the 3rd to 5th weeks after he ading. There was no significant difference between the treatments of s pikelet-clipping and male sterility. It was suggested that stem was th e most important alternative sink of carbohydrates when the sink deman d of panicles was reduced in rice. Although spikelet-clipping can affe ct the physiology of the rice plants in many aspects, it is still an u seful tool in studying the effect of sink removal on the distribution of assimilates.