Effects Of High Night Temperature On Protein Content And Cooking And Eating Quality Of Rice And Its Physiological Mechanism

Protein is the second largest storage substance in rice endosperm,and its content and composition have an important effect on cooking and eating quality.However,at present,the effect of night temperature on protein content and cooking quality of rice and its physiological mechanism are not clear.For this reason,a pot experiment was carried out from 2020 to 2021.Among them,10 rice varieties were planted in 2020 to compare the response of protein content and cooking and eating quality of different rice varieties to night temperature.Based on the results of the 2020 experiment,four rice varieties with different responses to night temperature were selected in 2021,including YY4949 and HHZ(whose rice protein content increased with the increase of night temperature),WSSM(whose rice protein content decreased with the increase of night temperature)and LLYHZ(whose rice protein content changed little with the increase of night temperature).The aim of this study was to explore the physiological mechanism of the effect of HNT on protein content and cooking and eating quality of rice.Night temperature treatment began after heading,including control treatment(CK,day / night average temperature was 30.2 / 22.2 ℃,respectively)and night high temperature treatment(HNT,day / night average temperature was 30.2 / 27.0 ℃,respectively).The main results are as follows:(1)The results in 2020 showed that night temperature and variety had significant interaction effects on rice appearance,cooking and eating,RVA parameters,protein and four protein components content.HNT significantly increased chalky rate,chalkiness,gel consistency,peak viscosity,breakdown viscosity value,albumin content,glutenin content and protein content,while significantly decreased grain length,grain width,amylose content,alkali spreading value,hot paste viscosity,cold paste viscosity and setback viscosity value.Among them,the protein content and gel consistency increased by 5.8%and 1.6% respectively,and the amylose content and alkali spreading value decreased by15.0% and 18.7%,respectively.(2)The 2021 study found that HNT significantly increased the rice protein content of YY4949 by 10.5%,and significantly decreased the rice protein content of HHZ,WSSM and LLYHZ by 5.0%,7.7% and 16.3%,respectively.The difference of protein content in rice at different night temperatures significantly affected the related indexes of cooking and eating quality.Correlation analysis showed that there was a significant negative correlation between taste value and the contents of protein,glutenin and globulin.(3)In 2021,it was found that the significant increase of protein content of YY4949 rice under HNT was related to the increase of glutamine synthetase(GS)activity in grains10 days after full heading.There was a significant positive correlation between protein content and GS,GOT and GPT activities of grains 20 days after full heading in four varieties under different temperature treatments.(4)In 2021,it was found that HNT significantly reduced the yield of YY4949 and HHZ by 22.5% and 11.20%,respectively,while the yield of WSSM and LLYHZ had no significant difference among different temperature treatments.Among them,the decrease of yield of YY4949 was mainly due to the decrease of seed setting rate and 1000-grain weight,while the decrease of yield of HHZ was mainly due to the decrease of 1000-grain weight.In addition,HNT caused early senescence in the late filling stage,which increased the respiration rate and decreased the photosynthetic rate.In a word,there were genotypic differences in the effects of night temperature on protein content and cooking and eating quality of rice,and there was a significant negative correlation between protein content and taste value of rice under different temperature treatments.HNT affects the protein content of rice by affecting the activities of enzymes related to nitrogen metabolism in grains.Future studies should further clarify the physiological mechanism of the effect of night temperature on rice protein content and the relationship between rice protein content and taste value.