Influence of High Temperature on Sucrose Metabolism in Chalky and Translucent Rice Genotypes
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Chalk is an unwanted and unpleasant opaque area in the rice grain caused by loosely packed starch granules possessing numerous air spaces. High temperature during grain filling favours induction of chalky grains; therefore, studying grain sink activity and carbon partitioning under these conditions would help to elucidate the difference in sucrose metabolism in chalky and translucent genotypes. Two rice genotypes viz., PAU-3699-13-2-1-1 (chalky) and PR122 (translucent) were sown at two different dates in order to expose the plants to different temperature regimes during grain filling. Significant increase in sucrose content, reduction in sucrose synthase (SuSy) and increased acid invertase (AIV) activity was observed during early transplanting (ET) when the crop encountered heat stress. Reduction in SuSy activity during ET did not allow cleavage of sucrose, thereby restricting the synthesis of starch. PAU-3699-13-2-1-1 exhibited higher acid invertase activity than PR122. The partially purified AIV exhibited optimum pH of 5.5 and 5.0 during ET, but 5.0 and 4.5 during normal transplanting (NT) in PAU-3699-13-2-1-1 and PR 122, respectively. The optimum temperature for AIV activity was 50 and 45 °C for the two genotypes during ET and NT, respectively. Changes in optimum pH, optimum temperature and Km of AIV during ET might be responsible for reduced accumulation of starch and increase in percent of chalky grains. Enhanced AIV activity may enable the grain carbon metabolism to adapt to high temperatures by providing hexoses for enhanced respiratory needs experienced during grain development.
KeywordsRice grains Transplanting dates Sucrose synthase Acid invertase Heat stress Chalk
The authors are thankful to Dr. G. S. Mangat, Sr. Rice Breeder—cum–Incharge for providing the necessary facilities and Dr. R. Kaur, Plant Breeder, for helping in carrying out field experiments. The authors declare that they have no conflict of interest.
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