Salt-tolerant Mechanism Of GSH Alleviates Salt-induced Stress In Tomato Seedlings

Secondary salinization of soil is one of the main obstacle factors limiting protected cultiva-tion and production in China.Tomato is one of the main crops in protected cultivation.Second-ary salinization of greenhouse soil lead to the decrease of photosynthesis and resistance of to-mato,and severe decline in yield and quality.Therefore,it is of great significance to study the salt tolerance mechanism of tomato seedlings under salt stress.Previous studies have shown that glutathione?GSH?acts as an antioxidant and signaling molecule that enhances plant resistance.Therefore,in this study,a hydroponic experiment was conducted and tomato?Solanum lycoper-sicum L.?cv.Zhongshu No.4 was used as experimental material.Different endogenous GSH levels and redox states were constructed by spraying exogenous 5 mM GSH?NG treatment?,1mM BSO?L-Buthionine-sulfoximine,GSH synthesis inhibitor??NB treatment?and BSO+GSH?NBG treatment?on leaves under salt stress.This study discussed the mechanism of GSH alleviate salt stress in tomato seedlings.The main results are as follows:1.Exogenous GSH inhibited the absorption of Na⁺and Cl^-and promoted the absorption of K⁺,Ca²⁺and Mg²⁺on roots and leaves of tomato seedlings under NaCl stress,and improved the ion content and selection transportation capacity in roots,stems and leaves,as well as the mi-crodomain distribution of ion in root and leaves under NaCl stress,so as to maintain ion homeo-stasis,thus alleviating the toxic effect of salt stress and improving the salt tolerance of tomato seedlings,and promoting the growth of tomato seedlings under salt stress.2.Exogenous application of GSH increase the expression levels and activities of en-zymes related to GSH synthesis and metabolism,including?-ECS,GS,GST,GPX and GR,and the contents of intracellular GSH and AsA and the ratios of GSH/GSSH and AsA/DHA in the salt-stressed plants or salt-stress plants treated with BSO.Application of GSH also significant enhanced the activities of SOD,CAT,POD and enzymes related to the ascorbate-glutathione cycle including APX,DHAR,MDHAR and GR,and decreased the contents of H₂O₂ and O₂.^-,lipid peroxidation.Therefore,application of exogenous GSH to salt-stressed tomato seedlings can be a successful strategy for enhancing ROS detoxification and regulating GSH synthesis and metabolism.These changes keep ROS levels low and maintain the cellular redox homeostasis.3.GSH application alleviated the inhibition of photosynthesis of salt-stressed tomato seedlings mainly by overcoming stomatal limitations,enhancing the efficiency of light utiliza-tion and dissipation of excitation energy in the PSII,balancing the absorbed light allocation to reduce ROS production and regulating chloroplast redox homeostasis and the antioxidant de-fense system to protect chloroplasts from oxidative damage.Thus,GSH regulates photosynthetic activities at the tissue level and ROS metabolism at the organelle level.This is one of the im-portant mechanisms to mitigate the inhibition of the reduction of photosynthesis caused by salt stress.4.Exogenous GSH not only reduced PAs by down-regulating the activities and expres-sion level of PA-synthesizing key enzymes?ADC and SAMDC?and up-regulating the activity and expression level of PA-degrading enzymes?PAO?,but also increased the ratio of Spd+Spm/Put by promoting the transformation of polyamines between different forms in NaCl-stressed plants with or without BSO treatment,thus improving the salt adaptability of to-mato seedlings.Therefore,exogenous GSH applied to salt-stressed plants can be a successful strategy for conferring salinity stress tolerance in tomato seedlings by modulating polyamine metabolism.5.The gene expression profiles of tomato seedlings treated with CK?control,nonstress?,N?NaCl stress?,NG,NB and NBG were analyzed using RNA-Seq technology.The differential-ly expressed genes of CK vs N,N vs NG,N vs NB and NB vs NBG were analyzed by statistics,GO and KEGG.It was found that there were 1600 DEGs in CK vs N,1098 DEGs in N vs NG,2117 DEGs in N vs NB and 623 DEGs in NB vs NBG.The unique 663 salt-tolerant genes in-duced by GSH were analyzed by differential expression.It was found that exogenous GSH can regulate the transcription level of Ca²⁺signal,phosphorylation and hormone signal transduction pathway,photosynthesis,glucose metabolism and stress protein genes under salt stress,and al-leviating the adverse effects of photosynthesis,redox homeostasis and energy metabolism of tomato seedlings under salt stress.6.Exogenous GSH can reduce the carbonyl content and increase the cysteine and sulfhydryl content to protect protein from oxidative damage in tomato seedling leaves under NaCl stress.This study using S-glutathionylation-non-target quantitative proteomics analysis,was found that exogenous GSH can mediate endogenous redox state to regulate the enzyme of Calvin-Benson cycle[including Ribulose-1,5-bisphosphate carboxylase small chain?rbcS?,Phosphoribulokinase?PRK?,Sedoheptulose-1,7-bisphosphate phosphatase?SBPase?and Ribu-lose-1,5-bisphosphate carboxylase large chain?rbcL?,etc]to maintain intracellular glutathi-onylation/deglutathionylation homeostasis of tomato leaves under salt stress,and improving the adaptability of tomato seedlings to salt stress.It is illustrates that S-glutathionylation based on redox state induced by exogenous GSH is involved in the formation of tomato seedlings salt tol-erant.