Grain growth, translocation of assimilates to the ear and photosynthesis are important processes to contribute to the formation of grain during the period of grain-filling in cereal crops. The objective of this investigation was to identify, for rice, which of these three proecesses is most affected by the water stress developed in grain-filling Perlod. We grew rice plants (Oryza Sativa, L. cv. Nipponbare) singly in 4 litter pots under outdoor conditions. The pots were kept flooded untill 15 days after anthesis. Then we transferred plants in a vinyl-covered house and stopped watering half the plants (deslccated). The rest of the plants were kept watered (control). Just before treatment, plants had their tillers removed to have four culms of approximately the same age. Plant water status was determined in terms of relative water content (RWC), being supplemented by measurements of the stomatal aperture and the transpiration rate. Plants were harvested before and after treatment, and dry weight was determined for unhuIled rices, rachis, top internode, lower internodes, leaf blades, leaf sheaths, crowns and roots. Progressive decline in RWC was more evident in plants subjected to soil desiccation. The change in stomatal aperture and transpiration rate with time also indicate that more severe stress developed in desiccated plants. But, there was little difference in dry weight increase in unhulled rice over 10 day period between control and desiccated plants, though the increase of total dry matter was reduced significantly in desiccated plants. This was accompanied by the greater decrease in dry weight of non-grain parts in desiccated plants. We therefore conclude that the water stress during the rapid growth of grain has little effect on grain growth as well as translocation in rice, while it reduces the rate of dry matter production considerably.
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