Abstract: Global temperature increase caused by climate warming is an obvious feature of climate change in recent years. With the global temperature rising, high temperature and heat damage of rice occur frequently. Especially in southern China, high temperature during grain filling has become an important factor restricting rice quality. The optimumaverage temperature for the grain-filling stage of rice is about 21℃. High temperature above 35℃ will significantly reduce the yield and quality of rice. The physiological process of carbon and nitrogen metabolism plays a key role in grain filling. As an important component of grain dry weight, the metabolism of starch and protein is affected by the physiological processes of carbon and nitrogen metabolismIn order to clarify the effect of high temperature on the physiological characteristics of carbon and nitrogen metabolism of rice grains during the early stage of filling, In this experiment,“Zhehexiang2”, a Japonica rice with good quality, was used as material. Two temperature gradients (31℃ / 24℃ (NT) and 35℃ / 28℃ (HT) were set up at the early stage of grain filling. After 5 days, 10 days and 15 days, and at harvest, the activities of key enzymes and related gene expression of starch, protein and adenosine triphosphate (ATP) formation in rice grain were observed and analyzed to determine the high temperature at the early stage of grain filling mechanism of effects on carbon, nitrogen and energy metabolism in rice grain. The results showed that, (1)compared with NT, HT treatment significantly reduced grain weight and starch content, while protein content increased. (2)Under HT treatment, the relative expression of sucrose transport genes OsSUT1 and OsSUT2 decreased significantly, while the activity of sucrose catabolic enzymes increased first and then decreased with the extension of the treatment time, resulting in the inhibition of sucrose supply under high temperature. (3)Compared with NT, the activities of key glycolytic enzymes hexokinase and pyruvate kinase decreased significantlyunder HT conditions; however the changes of key enzymes in the tricarboxylic acid cycle pathway showed significant differences under high temperature, citrate synthase. The activities of ɑ-ketoglutarate dehydrogenase and succinate dehydrogenase decreased significantly, while the activities of isocitrate dehydrogenase and malate dehydrogenase increased significantly.There was no significant difference in ATP and ADP between HT and NT. (4)Compared with NT, HT treatment significantly reduced the activity of ADPG pyrophosphorylase, and at the same time reduces the activity of granule-bound starch synthase and soluble starch synthase, resulting in the hindrance of amylose synthesis; the activity of starch hydrolysis-related enzymes has an upward trend. It showed that high temperature promotes the hydrolysis of grain starch. (5)Compared with NT, the total nitrogen content of grains under HT treatment had a rising trend, but the difference was not significant, the amino acid content had a significant rising trend, and the content of glutamic acid and ɑ-ketoglutarate increases significantly. The activities of nitrate reductase and nitrite reductase showed a downward trend, while the effect of high temperature on the activities of glutamate synthase and glutamine synthetase was not significantly different from that of optimum temperature. The test results showed that, the main reason for the hindrance of grain development at high temperature was that sucrose transport is hindered rather than sucrose utilization. At the same time, high temperature led to disorder of glycolysis and tricarboxylic acid cycle; grain starch synthesis was hindered at high temperature, while starch hydrolysis was enhanced; Process disorder and increased accumulation of ɑ-ketoglutarate are one of the reasons for the increase in protein content.Related research on energy metabolism involving ɑ-ketoglutarate can provide new ideas for the improvement of rice quality under high temperature.

Key words: Rice, High temperature during filling, Carbon and nitrogen metabolism, Energy metabolism, Sucrose transport, Sucrose utilization, Starch synthesis, Starch hydrolysis