Study On H₂O₂ Regulates Tomato Seedling Growth Under Salt Stress

Tomatoes are moderately salt-sensitive vegetables,and secondary salinization of facility soils severely limits the growth and yield formation of tomato seedlings under facility conditions.Therefore,it has great significance to carry out research to improve the adaptability of tomato salt.Predecessors and previous studies have shown that hydrogen peroxide?H2O2?as a signal molecule can enhance plant resistance.Therefore,in this paper,the seedlings of tomato variety“Zhongshu No.4”were used as experimental materials,pharmacological methods were used to construct different endogenous H2O2 levels by applying exogenous H₂O₂?N+H treatment?,DMTU?N+D treatment?and H₂O₂+DMTU?N+H+D treatment?to tomato seedling under NaCl stress.Studying the effects of exogenous H₂O₂ mediated endogenous H₂O₂ levels on growth,osmotic regulation,antioxidant enzymatic system and photosynthetic characteristics of tomato seedlings under salt stress to reveal the mechanism of action of H₂O₂ in plant salt tolerance stress,and provide a theoretical basis for further elucidation the formation mechanism of salt tolerance in tomato.The main conclusions are as follows:1.Compared with the control,NaCl treatment significantly reduced the chlorophyll content and root activity of tomato seedlings,inhibited the growth of plants and reduced the accumulation of biomass.Under NaCl stress,spraying exogenous DMTU,H₂O₂ and H2O2+DMTU could significantly reduce endogenous H2O2 level,increase chlorophyll content and root activity of tomato seedlings,promote plant growth and increase biomass accumulation.However,the promotion effect of exogenous DMTU and H₂O₂+DMTU on tomato seeding growth and endogenous H2O2 level were significantly lower than those of exogenous application of H₂O₂.It indicated that the low level of endogenous H₂O₂ were mediated by foliar application of DMTU,H₂O₂ and H₂O₂+DMTU under NaCl stress can significantly promote the growth of tomato seedlings under NaCl stress.However,exogenous H₂O₂ mediated the maintenance of a higher level of endogenous H₂O₂ in tomato seedlings,which is more conducive to promote growth and improve salt adaptability of tomato.2.NaCl stress significantly increased the MDA content of tomato seedlings,increased electrolyte permeability,aggravated membrane lipid per-oxidation,disrupted cell membrane structure,and inhibited the growth of tomato seedling.Under NaCl stress,foliar application of DMTU,H₂O₂ and H₂O₂+DMTU on the leaves reduced the MDA content and electrolyte permeability.In addition,the content of Pro increased.It indicated that the low level of endogenous H2O2 were mediated by foliar application of DMTU,H2O2 and H2O2+DMTU under NaCl stress can significantly alleviate membrane lipid per-oxidation induced by NaCl stress,maintain membrane integrity and maintain cell osmotic pressure balance,thus improving salt adaptability of tomato,and exogenous H₂O₂ mediated the maintenance of a higher level of endogenous H₂O₂ in tomato seedlings,which can better alleviate the damage of NaCl stress on the membrane of tomato seedling cells and induce the improvement of osmotic regulation.3.NaCl stress reduced enzymes activities of SOD,CAT,POD and the key antioxidant of AsA-GSH cycle in tomato seedlings,which resulted in the accumulation of H₂O₂,promoted membrane lipid per-oxidation,and exposed tomato seedlings to severe oxidative stress.Under NaCl stress,spraying DMTU,H₂O₂ and H₂O₂+DMTU on the surface of tomato seedlings leaves can adjust enzyme activities of SOD,CAT,POD and the key antioxidant of AsA-GSH cycle in different degrees,and reduce the level of endogenous H2O2.It indicated that foliar application of DMTU,H2O2 and H2O2+DMTU could alleviate the oxidative stress of tomato seedlings under NaCl stress in different degrees and sprayed H₂O₂ could better alleviate the damage of tomato seedlings caused by oxidative stress under the NaCl stress than sprayed DMTU and H₂O₂+DMTU.4.NaCl stress significantly reduced photosynthetic parameters Pn,Tr,Ci and Gs,increased VPD and WUE,significantly inhibited fluorescence parameters Fv/Fm,Y?II?,qP,and increased qN and Y?NPQ?values of tomato seedlings.It indicated that stomatal limitation was the main factor causing Pn decrease in tomato seedlings under NaCl stress,and tomato seedlings consumed excessive light energy of PSII by heat dissipation to adapt to salt stress environment,and tomato seedlings consume excess light energy of PSII by heat dissipation to adapt to salt stress environment.However,spraying DMTU,H₂O₂ and H₂O₂+DMTU on the surface of tomato seedlings leaves under NaCl stress could alleviate the inhibition of NaCl stress on photosynthesis of tomato seedlings by increasing the concentration and conductivity of intercellular photosynthetic substrates?CO₂?,promoting the activity and utilization efficiency of PSII photochemistry,stimulating energy and heat dissipation to protect photosynthetic apparatus from damage and other stomatal and non-stomatal constraints.The inhibition of NaCl stress on Photosynthesis of tomato seedlings could be better alleviated by exogenous spraying of H2O2 than spraying of DMTU and H₂O₂+DMTU.