Alleviation Effects Of Exogenous Methyl Jasmonate And Spermidine On Rice Under Heat Stress

In this study,Ningjing 3 and Wuyunjing 24 were selected as materials,plants were pot planted,and treated with high temperature during the booting and grain filling early stage,and Methyl jasmonate(MeJA)and spermidine(Spd)were sprayed to investigate the effects of exogenous chemicals under heat stress on rice yield,quality and physiological characteristics,and initially identified the mechanisms of MeJA and Spd in releiving heat damage.Main results are as follows:1.Organ temperature was increased by high temperature,exogenous MeJA and Spd reduced the increase rate of organ temperature.MeJA treatment slowed the rate of increase in leaf temperature caused by high temperature by 2.24%-5.07%at the booting stage under heat stress,MeJA reduced the increase amplitude of leaf temperature and panicle temperature by 3.72%-9.65%and 2.46%-6.70%at early filling grain stage.Spd had the same effect on organ temperature under heat stress.2.Photosynthetic system was hurted by high temperature,exogenous MeJA and Spd could reduce the damage of high temperature to it.Heat stress decreased the stomatal conductance(Cond),transpiration rate(Tr)and intercellular carbon dioxide concentration(Ci),and PSII was subjected to high temperature damage,which followed that actual photochemical efficiency(?PSII),photosynthetic electron transport rate(ETR),the energy ratio of photochemical reactions(Pr)were significantly reduced,and eventually decreased the net photosynthetic rate(Pn)under heat sress.During heat sress period,foliar spraying MeJA and Spd significantly increased Cond,Tr,(?PSII,ETR and Pr,ultimately the decrease amplitude of net photosynthetic rate under heat stress of booting stage was slowed by 9.64%through foliar spraying MeJA treatment.At early grain filling stage,MeJA and Spd had the same effects on photosynthetic system3.High temperature had some effect on rice plants,but there were much differences as the varieties and the stages are quite different,MeJA and Spd could enhance the antioxidant capacity and the balance of cell osmotic pressure.High temperature during booting stage decreased activities of SOD,POD,APX in leaves and inccreased the content of MDA,MeJA reduced the decrease range of SOD,POD and APX activity and the content of carotenoids,resulted in reduced the amount of MDA by 8.38%-55.43%.High temperature during early grain filling stage decreased the activities of SOD and POD of wuyunjing 24,while the performance in Ningjing 3 was quite the contrary,and the content of MDA were significantly increased due to serious high temperature stress,and high temperature stress induced the synthesize of large quantities of soluble sugar to maintain the balance of cell osmotic pressure at early grain filling stage,exogenous MeJA and Spd could significantly improve the activities SOD,POD,and the content of soluble sugar,resulted in reduced the amount of MDA by 7.76%-29.29%under heat stress.4.The content of endogenous hormones were altered by high temperature,exogenous MeJA and Spd enhanced it.At booting stage,high temperature improved the ABA and CTK content,MeJA increased the accumulation of ABA and CTK respectively by 12.65%-13.48%and 2.65%-17.00%.At early grain filling stage,high temperature stress caused a significant increase in content of ABA and a significant decrease in content of CTK in rice leaves,spraying MeJA could significantly increase the accumulation of ABA and CTK,the increase range was 10.97%-13.85%and 5.59%-19.01%,Spd had the same effect as MeJA.5.High temperature caused serious production loss,MeJA and Spd could alleviate the loss in yield.At booting stage,heat Stress reduced the grain number per panicle,grain length,grain width in both varieties and seed rate in Wuyunjing 24 significantly,and that resulted in a substantial decline in final yield,foliar MeJA under heat stress significantly increased the grain number of two varieties and seed set of Wuyunjing 24,finaly the production loss was down 2.87%-20.78%.At early grain filling stage,heat stress decreased seed setting rate and grain weight in both varieties,spraying MeJA and Spd significantly increased the seed rate in two varieties and grain weight of Ningjing 3 which finalily improved production under heat stress,the chemical substances respectily dcreased the yield loss by 11.24%-15.38%and 15.82%-16.80%.