Role Of Reactive Oxygen Scavenging System In The Formation Of Heat Tolerance Induced By The Interaction Of H₂S And ABA Signaling In Maize Seedlings

High temperature stress can lead to changes in plant morphology,physiological,biochemical and molecular levels,and then affects the growth,development and yield of plants.Maize（Zea mays L.）,as an important food crop,exploring the mechanism of its heat resistance has scientific significance.In this paper,maize seedlings were used as materials to explore the role of active oxygen scavenging system in the formation of heat tolerance induced by the interaction of H₂S and ABA signaling in maize seedlings.The results are as follows:In order to study the effect of H₂S and ABA signals on the formation of heat tolerance in maize seedlings,maize seedlings were treated with H₂S donor NaHS and ABA alone or in combination,and ABA was treated with H₂S inhibitors proparylene glycine（PAG）,hydroxyamine（HA）and scavenging hypotaurine（HT）.And NaHS combined with the ABA inhibitor sodium tungstate（ST）and fluriddone（FLU）followed by heat stress.The results showed that,compared with the control,NaHS and ABA alone could improve the survival rate and tissue viability of maize seedlings under high temperature stress,and reduced the relative electrical conductivity and malondialdehyde（MDA）content.Compared with NaHS and ABA alone,the combination of NaHS and ABA significantly improved the survival rate and tissue viability,and decreased the content of MDA.These results indicated that exogenous NaHS and ABA could induce the formation of heat tolerance in maize seedlings.In addition,compared with the control,the combination of ST and NaHS could improve the survival rate and tissue vitality of maize seedlings under high temperature stress,and reduce the relative conductivity and MDA content.The combination of FLU and NaHS could increase the tissue activity and decrease the relative conductivity of maize seedlings under high temperature stress.Compared with NaHS,the combination of ST and FLU with NaHS reduced the relative conductivity.Similarly,compared with the control,the combined treatment of PAG,HA and HT with ABA could improve the survival rate and tissue vitality of maize seedlings under high temperature stress,and reduce the relative conductivity and MDA content.Compared with ABA,the relative conductivity and tissue activity were improved.These results suggested that the interaction of H₂S and ABA signals was involved in the formation of heat tolerance in maize seedlings.In order to further clarify the interaction between H₂S and ABA signals,the contents of endogenous H₂S and ABA,as well as the activities of key enzymes for their synthesis,were measured in maize seedlings.The results showed that NaHS could increase the contents of endogenous H₂S,improved the activities of O-acetylserine mercaptan lyase（OAS-TL）,zeaxanthoxylate cyclooxygenase（ZEP）,9-cis-epoxide carotenoid dioxygenase（NCED）and ABA aldehyde oxidase（AAO）,decrease the expression of LCD1,and up-regulated the expression of NCED1.These effects could be attenuated by PAG,HA,or HT.ABA could increase the content of endogenous H₂S,improved the activities of D-cysteine dehydrhydrase（DCD）,L-cysteine dehydrhydrase（LCD）,NCED,ZEP and AAO,and up-regulated the expressions of LCD1,NCED1,ZEP and AAO.These effects could be weakened by ST or FLU.These further supported the interaction of H₂S and ABA signals.In order to further study the mechanism of heat resistance formation in maize seedlings,the activity of reactive oxygen scavenging system was measured.The results showed that before high temperature,compared with control,NaHS and ABA alone or in combination could significantly increase the contents of catalase（CAT）,glutathione reductase（GR）,ascorbate peroxidase（APX）dehydroascorbate reductase（DHAR）,and reduce the production rate of superoxide.After high temperature stress,the activities of peroxidase（POD）,superoxide dismutase（SOD）,CAT,GR,APX and DHAR and the contents of ascorbic acid（AsA）,total phenols,flavonoids and carotenoids were increased by NaHS and ABA alone or in combination.FLU and ST combined with NaHS could weaken the activity of NaHS-induced reactive oxygen scavenging system and reduce the expressions of CAT1 and DHAR.Compared with ABA alone,the activities of POD,CAT,DHAR and MDHAR,the contents of AsA,flavonoids,total phenols and carotenoids,and the total amount of ascorbic acid were significantly decreased by the combination of PAG,HA and HT with ABA,respectively.These results suggested that the reactive oxygen scavenging system regulates the formation of heat tolerance in maize seedlings induced by the interaction of H₂S and ABA.In conclusion,the interaction of H₂S and ABA signals could induce the formation of heat tolerance in maize seedlings,and the reactive oxygen scavenging system played an important role in the induction of heat tolerance in maize seedlings by such interaction.