Regulation Of Methylglyoxal Detoxification And Osmoregulation Systems On Heat Tolerance Induced By Glutamic Acid In Maize Seedlings

With the intensification of greenhouse effect,heat stress has become a main stress factor that restricts crop yield.Glutamic acid(Glu)is not only an amino acid,but also a signaling molecule.Our previous study revealed that Glu treatment is able to enhance the heat tolerance of maize(Zea mays L.)seedlings,but its mechanism is still elusive.Maize is not only the third grain crop,but also a model plant.Therefore,in this study,maize seedlings were used as experimental materials to study regulation of methylglyoxal detoxification and osmoregulation systems on heat tolerance induced by Glu in maize seedlings.The following results were obtained:Maize seedlings germinated for 60 h were primed with 90 m L of 0,0.5,1.0 and1.5 mmol/L Glu for 6 h.After Glu treatment,the maize seedlings were exposed to heat stress(45℃)for 16 h.The results showed that compared with the control,Glu treatment promoted the survival rate and tissue activity of maize seedlings,relieved electrolyte leakage,which indicated that Glu treatment increased the heat tolerance of maize seedlings.Moreover,0.5 mmol/L Glu was more suitable than other concentrations.In order to study whether MG detoxification system is involved in Glu-induced heat tolerance in maize seedling,the maize seedlings germinated for 60 h,treated with 0.5 mmol/L Glu for 6 h.After Glu priming,the corn seedlings were exposed to heat stress for 16 h.The results have showed that compared with the control,Glu pretreatment improved the content of MG,as well as the activities of glyoxalaseⅠ(Gly Ⅰ)and lactate dehydrogenase(LDH),but reduced the activity of aldose/aldehyde reductase(ALR);up-regulated the expression of Zm AKR1 gene in maize seedling under non-heat stress.Besides,compared with controls,Glu pretreatment improve the content of MG,the activities of Gly Ⅰ,glyoxalase Ⅱ(GlyⅡ),glyoxalase Ⅲ(Gly Ⅲ)and aldo-keto reductase(AKR);up-regulated the expression of Zm Gly Ⅱ,Zmaldr1 and Zm AKR1 gene in maize seedlings under heat stress.These indicated that methylglyoxal detoxification system regulated Glu-induced thermotolerance in maize seedlings.In order to explore the role of osmoregulation system in the formation of heat tolerance induced by Glu in maize seedlings,the maize seedlings germinated for 60 h were treated with 0.5 mmol/L Glu for 6 h.After Glu treatment,the maize seedlings were exposed to heat stress for 16 h.The results showed that compared with the control,Glu treatment increased the contents of proline(Pro),glycine betaine(GB)and soluble sugar,as well as the activities of delta1-pyrroline-5-carboxylate synthetase(P5CS),betaine aldehyde dehydrogenase(BADH)and trehalose-6-phosphate phosphatase(TPP)in maize seedlings under no-heat stress.The results also showed that compared with the control,Glu treatment increased the contents of Pro,GB,treholase(Tre)and soluble sugar,as well as the activities of BADH,TPP and trehalase,up-regulated the expressions of Zm P5 CS,Zm BADH and Zmtre1 gene in maize seedlings under heat stress.These results suggested that osmoregulation system was involved in the formation of heat tolerance induced by Glu in maize seedlings.In sum,Glu treatment was able to increase thermotolerance of maize seedlings,methylglyoxal detoxification and osmoregulation systems are involved in the formation of heat tolerance induced by Glu in maize seedlings.