Alleviated Effects Of Exogenous Sa On High Temperature Stress And The Underling Physiological Mechanisms In Wheat

Salicylic acid?SA?is a little phenolic molecule,distributed in a wide range of plant species.SA is one of the important hormones in plant.For a long time,SA is most known as a critical endogenous signal molecule to induce plant hypersensitive response?HR?and systemic acquired resistance?SAR?.However,in recent years many research found that SA acts as an important signaling molecule in plants to defense abiotic stress.The wheat cultivarYang Mai 16 was used as experimental materials to study the effects of different exogenous SA concentration pre-treatments on wheat thermotolerance and shift the optimal concentration of SA application to induce wheat thermtolerance.Pre-treatment with exogenous SA increased antioxidant enzymes activity and Fv/Fm,decreased relative electrolyte leakage rate and MDA content,alleviated lipid peroxidation of wheat leaves under heat stress.One of the optimal concentrations of SA is 0.01 mmol L-1 applied on the root and 0.1 mmol L-1 applied on the leaf to induce wheat thermotolerance,respectively.To explore the role of endogenous H₂O₂ in exogenous SA induced wheat heat tolerance,we analyzed 0.1 mmol L-1 SA-induced,which sprayd on leaves,dynamic changes endogenous H₂O₂ content.We found that sprayed exogenous SA can induce endogenous H₂O₂ accumulation fast,maximum at 30 min after SA application.Subsequently,H₂O₂ content sharply declined for 6 h,then did not obvious change.The acticity of SOD increased rapidly,peaked at 15 min after SA applied,but CAT and APX activity increased more temperately,peaked at 6 h after SA applied.Pre-treatment with exogenous SA increased antioxidant enzymes activity and Fv/Fm,decreased relative electrolyte leakage rate,as well as MDA?H₂O₂?O2-.content,alleviated lipid peroxidation of wheat leaves under heat stress.Thermo-protection obtained in SA-treated wheat seedings was time dependent,being maximal from 6 to 12 h after spraying.Wheat plants often suffer from heat stress during the grain-filling stage that finally reduction of yield and quality droping.Therefore,this experimental is to investigate the effects of foliar applied SA on protecting wheat from heat stress during the grain-filling stage.Our results showed that pre-treatment with exogenous SA and H₂O₂increased antioxidant enzymes activity,decreased MDA.H₂O₂ content,alleviated lipid peroxidation of wheat flag leaves as well as delayed plant senescence under heat stress.Besides,pre-treatment with exogenous SA and H₂O₂ increased Pn,Ti,Gs,thousand kernel weight and grain yield of wheat flag leaves under heat stress.Nevertheless,pretreatment of wheat with DMTU,a scavenger of H₂O₂,resulted in a significant reduction of SA-induced thermo-protection.These results indicated that applying exogenous SA with suitable concentration can induce wheat thermotolerance.Fiolar applied exogenous SA could induce endogenous H₂O₂ content transient changes.Therefore,H₂O₂ may act as a critical endogenous signal molecule in exogenous S A-enhanced thermotolerance in wheat.