Regulating Effect Of Exogenous Methyl Jasmonate On Response To Drought Resistance Of Wheat

Wheat(Triticum aestivum L.)yield ranked second in the world.About 40%of the world population take wheat as main food.However,there are nearly 100 million people suffered from chronic hunger in the world.A large scale of grain crisis had been broken in more than 30 countries and region.Therefore,high and stable yield of wheat are directly related to people's livelihood.With the deterioration of the global climate,the frequency and extent of drought will increase dramatically.Drought stress is one of the most complex environmental stress,which involved in a series of physiological and biochemical processe.Drought-induced loss in crop yield probably exceeds losses from all other causes.Therefore,it is very necessary to study drought resistance mechanisms of wheat and to establish the appropriate contingent measures.Among so many drought resisting techniques,chemical regulation technology is very popularity because of its advantages.Methyl jasmonate has been identified as a new kind of plant hormone that mediates divers developmental processes and defense responses against biotic and abiotic stress.In this research,hydroponics,tissue culture,pot culture and field cultivar were taken as cultivar methods,and methyl jasmonate were taken as a chemical regulation substance,systematic study regulating effect of exogenous methyl jasmonate on response to drought resistance of wheat to provide a theoretical basis and technical support in food safety production under drought stress.The main results are as follows:1.Drought stress significantly reduced fresh weight,dry weight and absolute water content.While,MDA,soluble protein content and root vitality were significantly increased.0.25?m of MeJA could significantly alleviate the decline of fresh weight,dry weight and absolute water content,and reduced membrane peroxidation product MDA content,increased root vitality and soluble protein content.Judging from phenotypes characteristics index and physiological index,0.25p.M of methyl jasmonate can significantly alleviate the negative influence of wheat seedlings under drought stress.2.Under mild drought and severe drought,the canopy temperature and total nitrogen content and its transport rates were increased,but the canopy NDVI values,dry weight,soluble sugar content and its transport rates were declined.The theoretical maximum weight of grains,the average filling rate,maximum grain filling rate emergence time,maximum filling rate and effective duration of grain filling were decreased.Effective number of spike,grain number and grain weight were decreased.Thus,the yield was decreased,but the water separation efficiency was increased.Spraying 0.25 ?M of exogenous methyl jasmonate significantly alleviated the negative influence of wheat seedlings under drought stress.3.Applications of MeJA enhanced adaptability to drought stress that included physiological and metabolic adjustments.In comparison with the control,drought stress decreased net photosynthetic rate(PN),stomatal conductance(gs),transpiration rate(E),and water use efficiency(WUE).The application of exogenous MeJA decreased gs and E,while increased WUE.MeJA mitigated the decline of PN,gs,and WUE induced by drought stress;it reduced the loss of photosynthetic C02 fixation caused by photosynthetic midday depression by 6-183%;while leaf temperature(LT)increased by drought stress and exogenous MeJA.Both drought stress and exogenous MeJA induced stomatal closure,which improved water status and delayed plant senescence due to drought stress.MeJA increased activity of SOD,POD,CAT,and decreased MDA content.PN-PAR response curves showed that MeJA mitigated the decline of maximum net photosynthetic rate(Pmax),apparent quantum yield(?),and saturation irradiance(Is)and the increase of compensation irradiance(Ic);dark respiration rate(RD)showed an additive effect when combined with drought stress.These results indicated that MeJA not only improved water status of wheat due to stomatal closure,but also induced the activity of antioxidant enzymes,which are resulted in mitigating the decline of photosynthetic characters and dry mass induced by drought stress,particularly during photoinhibition caused by photosynthetic midday depression.In addition,chlorophyll a+b,lutein content,Fv/Fo,Fv/Fm and?PS ? were decreased,xanthophyll cycle components(V+A+Z),xanthophyll cycle(A+Z)/(V+A+Z),Fo,NPQ and LUE were increased under drought stress.Spraying 0.25?M of exogenous methyl jasmonate alleviated the negative influence of wheat seedlings under drought stress.4.The endogenesis jasmonic acid(JA)content,activity of LOX,hydrogen peroxide(H2O2)content,antioxidant enzymes activities,level of reactive oxygen species(ROS),content of malondialdehyde(MDA),and cell viability were measured.The results showed that exogenous MeJA induced the activity of LOX and resulted in elevating endogenous JA level rapidly in a concentration-dependent manner;JA declined gradually after reaching its maximum.The level of H2O2 increased with increases in LOX activity and endogenous JA level,which are involved in the octadecanoid signaling pathway.However,SHAM inhibited LOX activity,the endogenous JA level,and the accumulation of H2O2 in wheat callus.In addition,the activities of several antioxidant enzymes increased after MeJA-pretreatment,but this effect was also inhibited by SHAM.The cumulative results suggest that H2O2 was generated through the octadecanoid signaling pathway,and some defense genes were provoked by the accumulation of H2O2.Therefore,we inferred that H2O2 might act as a signal molecule for the MeJA-induced antioxidant defense.Drought stress can be improved by MeJA-pretreatment,leading to decreases of endogenous malondialdehyde(MDA)and ROS contents,which are normally induced by drought conditions.Both drought stress and exogenous MeJA-pretreatment increased LOX activity,endogenous JA level,and antioxidant enzymes.Combinatory treatment showed an apparent synergistic effect on the activities of these antioxidant enzymes and resulted in improved cell viability.These results confirmed the hypothesis that H2O2 acts as a signal molecule for the MeJA-induced antioxidant defense and could alleviate the negative effects of drought stress on wheat callus.5.Drought and exogenous MeJA increased IAA levels in spike-stalk and root of wheat.Drought increased the IAA content in leaf,but exogenous MeJA decreased it;Drought and exogenous MeJA significantly increased the abscisic acid content in spike-stalk,flag leaf and root.While,drought significantly reduced spike-stalk,leaf and root GA1+3 and ZR content.Exogenous MeJA alleviate the decrease of GA1+3 and ZR.GA/ABA,GA/IAA,GA/ZR correlated significantly with yield in 0,10,and 20 days after flower,the correlation coefficients were-0.92,-0.97,-0.92,-0.98,-0.99,-0.99,-0.92,-0.97,and-0.92.6.H2O,MeJA,PEG and PEG + MeJA priming significantly improved wheat seed germination characteristics under drought conditions.Germination potential,germination rate,plant height,root length,root number,shoot dry weight,root dry weight,germination index and vigor index were increased.Soluble sugar,proline,and soluble protein content were increased.Antioxidant enzymes activity,such as SOD,POD,CAT and GR,were induced,and MDA content were decreased.7.Drought and exogenous MeJA significantly increased the LOX ability and endogenous JA content.Semi-quantitative PCR and quantitative PCR analysis showed LOX1 was mainly contribute to increase LOX activity under drought conditions,while LOX2 was mainly contribute to increase LOX activity under exogenous MeJA conditions,LOX3 and LOX4 had little effect on increasing LOX activity.Exogenous MeJA significantly induced up-regulation expressions of AOS and AOC.Drought and MeJA significantly induced OPR1 up-regulation expression.8.The 18680108,20769380,18117240 and 27503774 raw sequence were obtained in the four treatment samples by high-throughput sequencing.Then,18433566,20560147,17891454 and 27062892 high-quality sequence were acquired,respectively.After removing the repeat sequence,4773899,5545535,4277756 and 6806738 unique reads were obtained in the different samples.According to the length of the sequence analysis,the sequence were mainly 18-29 nt in length,which accounted for 99.19%,96.7%,98.32%,98.82%,respectively.In the total number of sequencing,the largest proportion was 24 nt in length,followed was 21 nt.Small RNA in four treatment were compared with wheat reference genome(EST)by using SOAP data analysis,the specific sequences were only 391,607(8.2%),452,778(8.16%),318,797(7.45%),510,881(7.51%)to match wheat ESTs reference sequence.From the predicted target genes,these differentially expressed miRNA mainly involved in plant growth and development in the process of signal transduction,hormone regulation,TCA cycle,osmotic regulation and other aspects of metabolism.