Mechanism And Regulation Of High Temperature At The Early Stage Of Grain Filling On Changes In Carbon And Nitrogen Metabolism Of Japonica Rice Grains

In recent years,the global abnormal climate has occurred frequently,and the high temperature and heat damage have become increasingly prominent,which has seriously restricted rice production.The physiological process of grain carbon and nitrogen metabolism plays a key role in grain filling,and the intermediate products of the tricarboxylic acid cycle mediate the process of carbon and nitrogen metabolism together.At present,there are relatively few studies on the relationship between energy metabolism and carbon and nitrogen metabolism in grains under high temperature.The relationship between starch and protein synthesis in rice grains under high temperature is not clear,and the mechanism of the related effects of carbon and nitrogen metabolism is unclear.In response to the above problems,this study used high-quality japonica rice Zhehexiang 2 in the middle and lower reaches of the Yangtze River as the material,planted in pots,and used an artificial climate box for high temperature treatment.relationship,clarify the regulation mechanism of nitrogen ear fertilizer on carbon and nitrogen metabolism under high temperature at the early stage of filling,and explain the mechanism of exogenous sucrose regulating grain carbon and nitrogen metabolism at high temperature at the initial stage of filling.It provides a theoretical reference for high-quality rice cultivation measures and variety selection for high-quality rice in the middle and lower reaches of the Yangtze River.The main findings are as follows:1.The mechanism of high temperature in the early stage of grain filling affecting the carbon and nitrogen metabolism of rice grains.1.The mechanism of high temperature in the early stage of grain filling affecting the carbon and nitrogen metabolism of rice grains.Research indicates:Compared with NT（optimal temperature）,HT（high temperature）treatment significantly reduces the grain weight and relative starch content,and increases the relative protein content.The relative expression of sucrose transport genes Os SUT1 and Os SUT2 decreased significantly under HT treatment,while the activity of sucrose decomposing enzymes increased first and then decreased with the extension of treatment time,resulting in the inhibition of sucrose supply under high temperature conditions.Compared with NT,the activities of the key glycolytic enzymes hexokinase and pyruvate kinase decreased significantly under HT conditions;while the changes in the activities of key enzymes in the tricarboxylic acid cycle pathway showed significant differences under high temperature,citric acid The activities of synthase,α-ketoglutarate dehydrogenase and succinate dehydrogenase decreased significantly,and the activities of isocitrate dehydrogenase and malate dehydrogenase increased significantly;under HT conditions,ATP（adenosine triphosphate）and ADP there is no significant difference between the total amount of adenosine diphosphate and NT.Compared with NT,HT treatment significantly reduces 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 shows that high temperature promotes the hydrolysis of grain starch.Compared with NT,the total nitrogen content of grains under HT treatment has a rising trend,but the difference is not significant,the amino acid content has a significant rising trend,and the content of glutamic acid andα-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.2.The mechanism of exogenousα-ketoglutarate affecting grain protein synthesis under high temperature.Research indicates:Compared with NT,HT treatment significantly reduced grain weight.Exogenous spraying ofα-ketoglutarate can help alleviate the effect of high temperature on grain weight,but the difference did not reach a significant level.Under high temperature,external sourceα-ketoglutarate has a significant effect on protein synthesis.The main reason is that exogenousα-ketoglutarate promotes the synthesis of amino acids in rice grains and the transport of amino acids from vegetative organs to the grains under high temperature.Exogenousα-ketoglutarate affects the process of energy metabolism,increasing the activity of isocitrate dehydrogenase（NADP-IDH）while reducing the activity ofα-ketoglutarate dehydrogenase（α-KGDH）,it promotes the accumulation ofα-ketoglutarate（α-KG）,and at the same time promotes the conversion of nitrate nitrogen（NO₃^--N）in the grains to amino acids,which increases the synthesis of amino acids.3.Mechanism of Nitrogen Regulating Carbon and Nitrogen Metabolism of Rice Grain under High Temperature.Research indicates that increase in nitrogen supply:will reduce the inhibitory effect of high temperature on Starch synthesis and promote protein synthesis;up-regulate the sucrose transport genes Os SUT1 and Os SUT2,promote sucrose transport,and at the same time increase the activity of SS-I.The conversion of sucrose to starch.Significantly reduces the ratio of amylose content to amylopectin content,which is conducive to the softening of rice to a certain extent,and improves the quality of cooking and eating.Significantly affects the tricarboxylic acid cycle（TCA）In the cyclic process,the intervention of nitrogen under high temperature conditions significantly increases the activity of NADP-IDH and promotes the synthesis ofα-KG.On the other hand,it reduces the activity ofα-KGDH and promotes the further accumulation ofα-KG.4.Effects of Exogenous Sucrose Supply on Carbon and Nitrogen Metabolism of Rice Grain under High Temperature.Research indicates that Exogenous sucrose:helps to alleviate the effect of high temperature on grain weight,and promotes the synthesis of protein and starch;it can be used as a signal molecule to promote the up-regulation of Os SUT1 and Os SUT4 at high temperature to alleviate the inhibition of high temperature on sucrose transport.Increasing the activity of GBSS,SSS and SBE promotes the synthesis of starch.On the other hand,reducing the activities ofα-amylase,β-amylase and starch phosphorylase related to starch hydrolysis will further accumulate strong starch.Exogenous sucrose Affect the energy metabolism process,by increasing the activity ofα-KGDH to promote the utilization ofα-KG to slow down the accumulation ofα-KG under high temperature.Increase the activity of NIR and GOGAT at high temperature,thereby increasing the ability of ammonia assimilation,which may promote protein content The main reason for the rise.