Response of Rice Starch Synthesis to Night Temperature Changes

【Objective】To clarify the effect of night temperature changes on rice starch accumulation, and to explore circadian changes of physiological characteristics of rice amylose/amylopectin formation at various night temperatures.【Method】High-quality japonica rice ‘Zhehexiang 2’ was subjected to three night temperature gradients of 31℃/20℃ (LT), 31℃/24℃ (NT), and 31℃/28℃ (HT) at the beginning of grain ripening stage, and the amylose and amylopectin contents, the key enzyme activities involved in amylose and amylopectin formation and the expression of related genes were measured at noon and midnight. 【Result】 The results showed that 1) compared with NT, LT and HT treatments significantly reduced grain weight and starch accumulation, LT and HT both reduced amylopectin content and increased amylose content, meanwhile the effect of HT was greater than LT. LT and HT treatments decreased grain pasting temperature and gel consistency, and had a significant influence on branched chain length. 2) The net photosynthetic rate of leaves under LT and HT presented no significant difference compared to NT, but LT and HT significantly reduced the accumulation of non-structural carbohydrates, meanwhile down-regulated the expression level of sucrose transporter genes OsSUT1, OsSUT2, and OsSUT4 both at noon and midnight. 3) LT and HT treatment reduced sucrose hydrolysis-related enzyme activities, meanwhile promoted starch hydrolase activities, resulting in increased soluble sugar contents, sugar utilization in grain was blocked. 4) Compared with NT, the adenosine diphosphate glucose content showed a downward tendency during the day and a rising trend at night under the treatment of LT and HT, which presented that the accumulation and utilization of adenosine diphosphate glucose were inhibited. And the granules bound starch synthetase activity were significantly reduced under LT and HT compared to NT with the prolongation of the treatment, and the enzyme activity at daytime was significantly influenced by temperature changing at night. 5) Compared with NT, LT and HT reduced the activities of night-time amylopectin synthesis-related enzymes and inhibited the expression of night-time related genes, which retarded formation of amylopectin, but the enzyme activities related to amylopectin synthesis was not significantly influenced by night temperature changing. 【Conclusion】High night temperature had a less effect on starch accumulation than low night temperature. High or low night temperature inhibited sucrose transport and metabolism, resulting in declined starch accumulation. The retarding of amylopectin formation was the main reason for the increase of relative content of amylose at high or low night temperature. Night temperature changes directly affected the metabolic process of starch formation at night, but the daytime activities of amylose-related enzymes were affected by night temperature changes, while the daytime activities of amylopectin-related enzymes were not significantly affected by night temperature changes.