Effects Of Different Salt And Alkali Stress On Proteome And Metabolome Of Cotton Seedlings

Objective: Soil salinization has seriously affected crop growth and brought serious challenges to agricultural production.However,the tolerance mechanism of cotton to salt and alkali stress is not completely clear.Therefore,this study explored the effects of different salt and alkali stress on cotton growth physiology,nutrient absorption and transportation,proteome and metabolome,clarified the tolerance mechanism of cotton under different salt and alkali stress,explored the molecular mechanism of cotton seedlings responding to salt and alkali stress,and laid a foundation for further research on cotton metabolism,specific protein and related gene functions under salt and alkali stress.This study provides a theoretical basis for cotton breeding and cotton cultivation on different types of saline alkali land.Methods: In this study,the pot experiment was conducted,and the control,salt stress（NaCl）and alkali stress（Na HCO₃+Na₂CO₃）were set up.The effects of salt and alkali stress on cotton growth and physiology were studied by measuring cotton biomass,adversity physiological indicators,photosynthetic parameters,and enzyme activities.The effects of salt and alkali stress on the absorption and transport of nutrient elements in cotton were clarified by measuring the ion concentrations in various organs of cotton.Through the proteome sequencing of cotton leaves and roots,the differential proteins in cotton leaves and roots were screened,and the GO analysis and KEGG analysis of the differential expressed proteins were carried out to explore the response mechanism of cotton to different salt and alkali stress.The specific pathway of the effect of different salt and alkali stress on cotton metabolism was analyzed by measuring the metabolic groups of cotton leaves and roots.Results:（1）Compared with the control,salt stress and alkali stress significantly reduced cotton biomass,significantly increased leaf relative conductivity,malondialdehyde content,superoxide dismutase activity,peroxidase activity,catalase activity,and proline content.Salt stress significantly reduced the net photosynthetic rate,stomatal conductance,transpiration rate,intercellular CO₂ concentration and chlorophyll content of cotton leaves,but alkali stress had no significant effect on it.（2）Compared with the control,salt and alkali stress significantly increased the concentration of Na in cotton organs.Salt stress reduced the contents of P,K,Ca,Mg,S and Cu in cotton leaves,and the contents of N,Ca,B and Fe in roots.Alkali stress reduced the contents of N,P,Ca,Mg,S and B in cotton leaves,and the contents of N,Fe,P,S,Ca and Zn in roots.Under salt stress,the absorption capacity of P,Mg,K,S and Cu increased,but the transport capacity decreased,the transport capacity of B,N and Fe increased,and the absorption and transport capacity of Mn,Zn and Mo increased;Under alkali stress,the absorption of Mg and B is promoted,the transport capacity is inhibited,the transport capacity of Zn and Fe is improved,the absorption and transport of N,P,S,and Ca are inhibited,and the absorption and transport capacity of Mn,Mo,Cu,and K is improved.（3）458 differential proteins were detected in cotton leaves under salt stress,which were mainly concentrated in benzodiazepines biosynthesis,photosynthesis and amino acid biosynthesis;Under alkali stress,240 differential proteins were identified,which were mainly concentrated in benzodiazepines biosynthesis,valine,leucine and isoleucine biosynthesis and monoterpene biosynthesis.1725 differential proteins were detected in cotton roots under salt stress,which were mainly concentrated in flavonoid biosynthesis,phenylalanine biosynthesis and glycolysis/glucose production pathways.75 differential proteins were identified under alkali stress,which were mainly concentrated in flavonoid biosynthesis,phenylalanine biosynthesis and galactose metabolism.Nine differential proteins related to photosynthesis were identified in the leaves,among which pet B,pet F,psa D,psa F,psb A,psb B,psb C,and psb O decreased under salt stress,while Psb S increased under alkali stress.（4）A total of 99 differential metabolites were screened from cotton leaves under salt stress,93 of which were up-regulated,accounting for the absolute majority.The differential metabolites were mainly clustered in organic acids,sugars,amino acids,and their derivatives,alcohols and amines;A total of 179 differential metabolites were screened under alkali stress,and 96 were up-regulated metabolites,which did not account for the absolute majority.The differential metabolites were mainly clustered in amino acids and their derivatives,organic acids,sugars,lipids and lipoids.A total of 90 different metabolites were screened from cotton roots under salt stress,with 72 up-regulated metabolites accounting for the absolute majority.The differential metabolites were mainly clustered in organic acids,amino acids and their derivatives,sugars and alcohols.A total of 181 metabolites were screened under alkali stress,with 108 up-regulated metabolites accounting for the absolute majority.The differential metabolites were mainly clustered in amino acids and their derivatives,organic acids,sugars,and amines.KEGG pathway enrichment analysis showed that pentose phosphate pathway,pyruvate metabolism and terpene main chain biosynthesis were enriched in leaves under salt stress,while galactose metabolism,butyric acid metabolism and arginine biosynthesis were enriched in leaves under alkali stress;Linoleic acid metabolism,tryptophan metabolism and lysine degradation are enriched in the roots under salt stress,while citric acid cycle,starch and sucrose metabolism,and glyoxylic acid and dicarboxylic acid metabolism are enriched in the roots under alkali stress.Conclusions: Salt and alkali stress significantly inhibits cotton growth.Salt stress inhibits the process of light capture,light utilization efficiency,and electron transfer in cotton leaves,which is one of the reasons why salt stress leads to the inhibition of cotton photosynthesis.Enhancing the accumulation of organic acids,sugars,nucleotides,nucleotides and their derivatives,as well as amino acids and other metabolites in leaves and roots,as well as energy metabolism and amino acid synthesis and metabolism such as glycolysis,TCA cycle,and 2-oxycarboxylic acid metabolism in leaves,are the main pathways for salt stress tolerance;Enhancing the accumulation of organic acids and sugars in the roots,as well as metabolic activities such as butyric acid metabolism,pentose phosphate pathway,TCA cycle,and pyruvate metabolism in the roots,are key mechanisms for cotton to respond to alkali stress.