| Rice is one of the most important crops in the world and provides human protein and energy.With the intensification of global warming,the probability of high temperatures encountered during filling stage of rice is increasing,which resulted in poor rice quality.Nitrogen application,as a traditional cultivation measure,plays an important role in dealing with the negative effect of elevated temperature on quality,but its regulatory mechanism is not clear.The relationship between starch and grain formation has been basically clear,but the relationship between nitrogen metabolites and grains has not been paid enough attention.In this study,Jiangsu conventional japonica rice Wuyujing 3 was used as the experimental material,and four treatments were set,namely,ambient temperature(CK),elevated temperature(ET),application of nitrogen fertilizer under normal temperature(CKN),application of nitrogen fertilizer under elevated temperature(ETN).This study explored the changes of rice yield and quality,accumulation of grain storage substances,nitrogen metabolism enzymes and regulatory factors under warming and nitrogen treatment to comprehensively clarify the physiological mechanism of warming and nitrogen fertilizer regulating grain storage protein and quality formation.The main results are as follows:1.Warming affected rice growth,significantly reduced rice yield,and nitrogen fertilizer could alleviate this effect.The net photosynthetic rate of rice varied with different growth stages under warming and nitrogen fertilizer.In the case of warming,the early grain-filling rate was obviously accelerated,and the late grain-filling rate decreased rapidly,which shortened the grain-filling period.The yield had a significantly loss because of the reduction of1000-grain weight and seed setting rate under open-field warming,which decreased by23.72% and 11.45% respectively in two years.Nitrogen application under warming could slow down the early grain-filling rate,increase the 1000-grain weight,compensate for the loss of yield,which was increased by 16.09%,7.25% respectively.2.The accumulation of storage substances such as starch and protein changed under nitrogen fertilizer and warming conditions,thereby regulating the formation of quality.Chalkiness significantly was increased,the length and width of grain and the head rice rate significantly were reduced under open-field warming,the application of nitrogen fertilizer under open-field warming had a mitigation effect,the chalkiness were decreased by 22.27% and 20.61%,the head rice rate were increased by 4.34% and 4.68%respectively in two years,which improved grain quality.Warming and nitrogen affected endosperm development,thus affecting storage matter accumulation.Warming accelerated the development of protein body and amyloplast,and the application of nitrogen fertilizer under open-field warming could coordinate the development.Warming and nitrogen fertilizer could regulate storage protein content by regulating carbon and nitrogen balance,and further regulate rice quality.Under open-field warming condition,the contents of total starch,amylose,prolamin subunits and prolamin in rice grains were decreased,while the contents of precursor subunit,glutelin and amino acid increased,but there was no significant difference in the relative content of most amino acids.With the application of nitrogen fertilizer under open-field warming,prolamin,glutelin precursor and acid subunits,glutelin and amino acid content further increased.Warming and nitrogen fertilizer had a superposition effect on amino acid and total protein content.In addition,nitrogen application could alleviate the decrease of glutelin under elevated temperature,indicating that nitrogen fertilizer might regulate grain quality by affecting prolamin content.3.Nitrogen metabolism enzyme activity enhanced,promoting the accumulation of protein and amino acid under nitrogen fertilizer and open-field warming.The change of nitrogen metabolism enzyme activity in grains under different treatments will affect protein synthesis.The GOGAT enzyme activity in the early grain filling stage,GPT and GOT enzyme activity increased and GS enzyme activity decreased under the open-field warming.The activities of GOGAT,GOT in the early filling stage were further increased with the application of nitrogen fertilizer under elevated temperature,which increased by 13.32% and 5.83%,nitrogen fertilizer could alleviate the decrease of GS enzyme activity in the early filling stage,which was increased by 21.05%.The results showed that the effect of nitrogen fertilizer on enzyme activity was mainly affected in the early filling stage.The increase of these enzyme activities promoted the synthesis of protein,increasing the protein content.4.Nitrogen fertilizer and warming affected protein synthesis factors and regulated protein synthesis.Factors related to grain storage protein synthesis affect protein synthesis.The synthesis of glutelin was regulated by Glu A and Glu B subfamily genes.The relative expression of Glu A1,Glu A2,Glu B5 and Glu B1 in the middle grain-filling stage increased under open-field warming.The relative expression of Glu A2,Glu B1 further increased by38.76% and 54.14% with the application of nitrogen fertilizer under open-field warming,indicating that warming and nitrogen application promoted the synthesis of glutelin by promoting the expression of Glu A and Glu B genes.The synthesis of prolamin is regulated by Pro14,the relative expression of Pro14 increased by 2.09% in the early grain-filling stage,and decreased by 33.04% in the middle grain-filling stage under warming condition,the relative expression of Pro14 increased with the application of nitrogen fertilizer under open-field warming,which was consistent with the change of prolamin content,indicating that the synthesis of prolamin is regulated by the relative expression of Pro14.The synthesis of glutelin and prolamin is also regulated by regulatory factors Bip and PDI.The relative expression of PDI and Bi P were decreased in the early filling stage,and increased in the middle filling stage under the open-field warming,the application of nitrogen fertilizer under open-field warming or not had no significant difference on Bi P.The relative expression of PDI further increased with the application of nitrogen fertilizer under open-field warming.Warming and nitrogen regulated prolamin and glutelin synthesis by affecting the expression of Bi P and PDI.In conclusion,increased temperature led to the decrease of grain yield and quality.Warming and nitrogen fertilizer affected storage protein synthesis factors Glu A 、 Glu B subfamily genes,Pro14 genes and related regulatory factors Bi P and PDI,nitrogen metabolism enzyme GOGAT,GS and GPT,GOT enzyme activity,which regulated storage protein synthesis,thus induced the changes in the accumulation balance of storage proteins,amino acids and starches,which coordinately controls the quality of grain.The application of nitrogen fertilizer under open-field warming alleviated the rapid early grain filling rate and protein body development,not only make up for the loss of yield,but also improve the grain quality,which is important for further guiding the actual production of rice and coping with climate change. |
PDF Full Text Request