The Function Of Hydrogen Peroxide And Glutathione On Spermidine Regulating Tomato Seedlings Salinity-alkalinity Tolerance

Tomato is an economically effective crops,which plays an important role and is suitable for cultivation in neutral or weak acidic soils.In recent years,due to the environmental characteristics of high temperature and high humidity in the facilities and the inappropriate field management,the phenomenon of soil secondary salinization in the facilities has been aggravated year by year,which has seriously affected the normal growth and development of tomatoes,reduced yield and quality of tomatoes and caused great losses to the production of tomato in the proteced agriclture.Therefore,it is of great significance to explore ways to alleviate the damage caused by salt and alkali stress in tomato production facilities.Spermidine（Spd）is a kind of polycationic macromolecule widely distributed in plants,which can regulate the growth and development of plants and alleviate the damage caused by stress.Studies have shown that exogenous Spd can effectively alleviate the damage caused by salinity-alkalinity stress on tomato seedlings,but its molecular modulation mechanism is still unclear.In this study,the tomato inbred line Ailsa Craig was used to study the effects of pre-spraied exogenous Spd on the growth,balance of redox and Na⁺and K⁺homeostasis of tomato seedlings under saline-alkali stress.To investigate the signal transduction mechanism of polyamine secondary metabolites,hydrogen peroxide（H₂O₂）and glutathione（GSH）,on the salinity-alkalinity tolerance of tomato seedlings treated with pre-spraied exogenous Spd.The main results are as follows:1. Spd pre-treatment can alleviate the oxidative stress damage of tomato seedlings under saline-alkaline stress.Exogenous Spd pre-treatment significantly promoted the expression of Sl CAT1（Catalase gene）and Sl APX5（Ascorbate peroxidase homolog 5）,and significantly increased the activity of superoxide dismutase（SOD）,catalase（CAT）,dehydroascorbate reductase（DHAR）and ascorbate peroxidase（APX）,and reduced the relative conductivity（REC）,the accumulation of malondialdehyde（MDA）and the production rate of superoxide anion（O₂^-）in tomato leaves,and reduced the commucationg of ROS that induced by salinity-alkalinity stress,alleviate the oxidative damage caused by saline-alkali stress,maintain the stability of cell membrane,and alleviate the inhibition of saline-alkali stress on the growth of tomato seedlings.2. Under salinity-alkalinity stress,exogenous Spd pretreatment can maintain the Na⁺/K⁺homeostasis in tomato seedlings.Salinity-alkalinity stress conditions significantly increased the Na⁺content of tomato seedlings,the Na⁺/K⁺ratio and reduced the content of K⁺in tomato seedlings.The Spd pretreatment can raise seedling leaf the expression of genes（NHX1-3）encoding the Na⁺/H⁺transporters and reduce the excessive accumulation of Na⁺in tomato seedling under salinity-alkalinity stress,promote the absorption and transportation of K⁺,reduce the plant root,stem and leaf in Na⁺/K⁺ratio,maintain Na⁺/K⁺homeostasis,alleviate ion poisoning caused by salinity stress on tomato seedlings.3. Spd pretreatment may regulate the salinity tolerance of tomato by secondary metabolism to H₂O₂as a signal molecule produce.Under normal cultivation conditions,exogenous Spd treatment can induce the generation of H₂O₂,and after 24 h of exogenous Spd pretreatment,the accumulation of H₂O₂in tomato seedling leaves was significantly reduced under short-term stress compared with those under direct saline treatment,indicating that exogenous Spd pretreatment may regulate the salinity tolerance of tomato by secondary metabolism to H₂O₂as a signal molecule produce.The application of DMTU and DPI significantly increase of MDA content,REC and generation rate of ultra-oxygen anion,and increase the tomato oxidative damage under salinity-alkalinity stress,the exogenous H₂O₂pre-treatment can alleviate the damage of plant caused by salt stress;the application of DMTU and DPI does not eliminate the mitigative effect of exogenous Spd on plant under salinity-alkalinity stress,and the Spd can’t induce the expression of RBOH1 genes which encoding NADPH oxidase,which indicate the raised of hydrogen peroxide caused by Spd treatment was not caused by NADPH oxidase.The effect of Spd pretreatment on plant under salinity-alkalinity stress is mediated by H₂O₂which was produced by other pathways,rather than by NADPH oxidase.4. GSH play an important role in Spd pre-spray regulating saline-alkali tolerance of tomato seedlings.Under saline-alkali stress,GSH treatment can significantly reduce the relative conductivity of tomato leaves,reduce the accumulation of ROS in tomato seedling leaves,and alleviate the damage of membrane peroxidation,enhance the saline-alkali resistance of tomato seedlings.The application of BSO significantly inhibit the saline-alkali resistance of tomato induced by Spd pretreatment and saline-alkali resistance of tomato seedlings induced by H₂O₂was significantly weakened;the saline-alkali resistance of tomato seedlings induced GSH weakened after application of DMTU and DPI.To sum up,H₂O₂and GSH can play a synergistic role in exogenous Spd pretreatment to regulate salt and alkalinity tolerance of tomato seedlings,alleviate the oxidative damage of plants,and improve the ability of antioxidant stress of tomato plants under saline-alkali stress.