The Mechanism Of Energy Metabolism Mediating Rice Heat Resistance

These years,extreme high temperature climates frequently occur,that seriously threatens the food security of China,and even the world.Cultivating heat-resistant rice varieties and developing risk-resistant cultivation techniques are efficient to deal with global warming.The studies about heat damage have made great progress,but it still cannot meet the demand of production.High temperature and other stress can interfere with carbohydrate metabolism and energy balance,and inhibit antioxidant capacity and heat shock protein accumulation,leading to yield loss and quality damage of rice.However,the mechanism of energy metabolism affecting heat resistance is still unclear.In this study,several rice varieties with different genotype and phenotypes were used to research the role of energy metabolism in heat response,and elucidate its mechanism.Under the background of global warming,we also discussed energy production,utilization and distribution in the role of yield formation and heat resistant which can provide theoretical basis for heat resistant breeding and cultivation developing.Four rice varieties,Huazhan(HZ)and its GS2 near-isogenic line(HZ^-GS2),Nipponbare(NIPP,WT)and its mutant(hts)with rolling leaf phenotype,were planted in pots.Different temperatures with climate chamber simulate high temperature and nitrogen levels were set at seedling stage,meiosis stage and anthesis stage.The results were as below.1.Energy deficiency results in a decrease in heat resistance of rice.NIPP(WT)and hts seedlings were subjected with 40?.Under heat stress,leaf temperature,respiration rate,ABA and H₂O₂ contents of hts were significantly higher than that of WT,but leaf transpiration rate and stomatal conductance of WT were significantly lower than that of the hts.In addition,the expression levels of HSP71.1 and HSP24.1,carbohydrate,ATP,NAD(H)content and dry matter weight increased significantly in WT leaves than that in hts.More importantly,exogenous ABA significantly reduced the heat resistance of hts,but significantly increased the heat resistance of WT.ABA significantly increased carbohydrate,ATP,NAD(H)content and HSPs expression in WT under high temperature,but significantly decreased it in hts.In conclusion,we suggest that ABA treatment at high temperature increases the energy consumption of leaf-rolling rice,leads to energy deficiency,and aggravates its high temperature injury.2.Improve the energy production efficiency can increase heat resistance of rice.HZ and HZ^-GS2 seedlings were subjected with 45?.The heat resistance of HZ^-GS2was higher than that of HZ,and the increase of H₂O₂,MDA and REC in the leaves of HZ^-GS2was lower than that of HZ.Meanwhile,the antioxidant capacity and heat shock protein accumulation of HZ^-GS2 were higher than that of HZ.GS2 mediated heat resistance of rice may relate to energy metabolism.Under heat stress,there was little difference in the decrease of carbohydrate between the two rice plants,but ATP content,energy charge and ATPase of HZ^-GS2 leaves increased,while decreased significantly in HZ.It was speculated that GS2 could improve energy utilization efficiency and heat resistance of rice by increasing ATPase activity.Further studies showed that exogenous GA₃ could increase the activity of ATPase in leaves,which can increase of ATP and energy charge,improve the heat resistance of rice.3.Increasing nitrogen level can enhance energy production,optimize energy allocation,and improve energy utilization efficiency,resulting in heat resistance.HZ and HZ^-GS2 planted in pots with different nitrogen levels treatments were subjected with 38?for 7d in climate chamber at meiosis and anthesis stages,respectively.High temperature significantly decreased spikelet fertility,and appropriate nitrogen fertilizer treatment could alleviate high damage,but the response of HZ and HZ^-GS2 to nitrogen was different.Under high temperature,pollen fertility,pollen germination rate and pollen tube elongation of HZ increased first,then decreased with the increase of nitrogen level,but they always increased at HZ^-GS2,suggesting that GS2 can improve nitrogen use efficiency.Nitrogen had little effect on carbohydrate in anther or spikelet,but it significantly increased the activity of acid invertase and ATPase expression.In concluding,N enhances energy utilization efficiency and heat resistance of rice by mediateing energy production and utilization.4.Based on the previous studies and the background of global warming,HZ and NIPP planted in pot with different temperatures treatments in climate chambers,to investigate the effects of energy production,energy allocation and energy utilization on dry matter loss.Recently,many studies have suggested that breeding rice varieties with high photosynthetic efficiency through transgenic or gene editing are an effective way to deal with high temperature,but we think that it is respiration rather than photosynthesis determin dry matter and yield loss of rice.Moderate high temperature(?40?)had little effect on the net photosynthetic rate of rice leaves,but significantly increased the respiration rate.In addition,high temperature significantly increased the activity of mitochondrial complex,but significantly decreased the activity of alternating oxidase(AOX),ATP content and dry matter weight.These results indicate that moderate high temperature increases energy production efficiency,but most of the energy is allocated to maintenance respiration,resulting in a decrease in energy utilization efficiency.Therefore,under the background of global warming,breeding rice varieties with low respiration and high energy efficiency is one of the important ways to solve the world food crisis.