Relationship Between Physiological-Biochemical Changes Under High Temperature Condition And Chalkiness Formation In Early Season Indica Rice

Chalkiness is the opaque part formed by the inconsistent arrangement of amyloid and protein bodies in the endosperm of rice.It seriously restricts the improvement of the quality of early indica rice in southern of China.The grain-filling period is an important time for rice yield and quality.The heat stress in that time has an important influence on chalkiness formation.To investigate the relationship between physiological-biochemical changes under high temperature condition and chalkiness formation in early season Indica rice,three early season Indica rice varieties Xiangzaoxian 7（X7）,Xiangzaoxian 11（X11）and Xiangzaoxian24（X24）were conducted as materials to treat with high temperature（HT）for 15 days from the 4_th day after heading（DAH）.At the same time,we analyzed the relationship between flag leaf net photosynthetic rate,grain filling rate,grain dehydration rate,antioxidant capacity,grain soluble protein content,grain amylose content,grain mineral element content,expression of starch synthesis-related gene at grain-filling stage chalkiness formation under high temperatures condition.The results are as follows:1.Under high temperature condition,the high chalky X24 and X11 have two rapid dehydration.the dehydration rate of X24 increased in the first rapid dehydration,and the second rapid dehydration（mature dehydration）of X11 and X24 was advanced.Under high temperature condition,the grain initial filling rate of X11 increased significantly,The grain filling rate of X7 and X24 did not rebound as NT in 20 DAH.Therefore,high temperature treatment changes the rate of grain dehydration and filling,resulting in insufficient and discontinuous grain filling,reduced grain fresh and dry weight,and increased chalkiness.2.Under high temperature conditions,the net photosynthesis and stomatal conductance decrease of X7,X11 and X24 flag leaves,and the high chalkiness X11 and X24 are more severely reduced than the low chalkiness X7,thus photosynthetic compounds supply insufficient;the lipid membrane peroxidation in rice grains and flag leaf cells increasesed,and the content of MDA,POD and SOD activity of flag leaf increased,POD and SOD activity of grain and antioxidant capacity decreased under high temperature.indicate the high temperature caused the imbalance of the antioxidant enzyme system in the grains,resulting in abnormal starch synthesis in the grains and increased chalkiness.3.The content of most mineral elements in low chalky X7 grains is higher than that of high chalky X11 and X24;High temperature treatment leads to lack of As,Mn,Zn,Mg,Ca in X7 and X24 grains,Possibly by affecting the level of grain metabolism,inhibiting the synthesis of starch and protein,resulting in insufficient filling and chalkiness.4.the expression of starch synthesis-related genes（SSIIIa、AGPSL2 and GBSSI）were significantly down-regulated at 12 DAH and 16 DAH in high chalky grains（X11 and X24）under high temperature conditions,causesing amylose content decreased and chalkiness increase in rice grains.In summary,this paper analyzes the physiological-biochemical changes of rice after high temperature treatment during grain-filling period,we found that leaf net photosynthesis rate,grain filling rate,grain dehydration rate,antioxidant capacity,soluble protein,grain amylose content,grain mineral element content,and starch synthesis-related gene expression were closely related to chalkiness formation caused by high temperature.It provides the important evidences for analysis of physiological-biochemical mechanism of the chalkiness formation in early season Indica rice induced by high temperature.