Physiological Response And Transcriptome Sequencing Analysis Of Barley Seedlings Under NaCl Stress

Soil salinization is one of the main limiting factors affecting the high and stable yield of crops,and barley breeding is facing great challenges under the influence of saline-alkali stress.In this study,Long 09Y1-199（salt-tolerant material）and Hu 90-6573（salt-sensitive material）were used as experimental materials to study the morphological characteristics and physiological indicators of barley seedlings roots and leaves under NaCl stress.By means of transcriptome analysis,this study focused on changes of differentially expressed genes in roots of sensitive&resistant materials in response to salt stress,as well as the screening of key candidate genes.This study aimed to reveal the physiological and molecular basis of barley response to salt stress,and to provide theoretical support for the screening and identification of barley salt-tolerant germplasm resources and the selection of varieties.The main findings are as follows:1.As NaCl concentration increased,1)the fresh and dry weight of aboveground&undergroundparts,root length,root surface area and root volume of Long 09Y1-199 and Hu 90-6573 showed a downward trend;2)the relative growth rate and root activity initially increased and subsequently declined,peaking under the treatment of 100 mmol/L NaCl,indicating that low-concentration salt stress could promote growth;3)the relative growth rate hit the bottom under the treatment of 500mmol/L NaCl;4)the wilting coefficient showed an upward trend;5)Long 09Y1-199 outperformed Hu 90-6573 in various growth and development indicators.2.As NaCl concentration increased,1)the SPAD value of barley leaves declined,while Long 09Y1-199 still outperformed Hu 90-6573;2)the contents of proline,betaine and soluble sugar in leaves and roots showed an upward trend,and Long 09Y1-199defeated Hu 90-6573 in the accumulation of osmotic adjustment substances;3)O₂^-,MDA,H₂O₂contents continuously increased,which didn’t significantly influence the growth of experimental materials when the NaCl concentration reached 100mmol/L,whereas it had a greater negative impact on the growth of Hu90-6573 than Long 09Y1-199 under the treatment of high concentration NaCl（i.e.≥300mmol/L）;4)the activity of SOD,POD and CAT kept growing,and Long 09Y1-199 was superior to Hu 90-6573 in the overall activity of various enzymes;5)Long 09Y1-199 defeated Hu 90-6573 in the reaction of ascorbic acid-glutathione circulatory system by a large margin.3.In the three comparison groups of two stages of development,this study carried out Venn analysis on the DEGs of Long 09Y1-199 and Hu 90-6573,detecting that 108 and499 co-expressed DEGs accounted for 2.62%and 6.67%of total DEGs,respectively.When performing Venn analysis on the comparison group between the two varieties,1648co-expressed DEGs were screened.Such differential genes are mainly involved in metabolic processes,cellular processes,biological regulation,response to stimuli,binding,catalytic activity,transporter activity,etc.Pathways only significantly enriched in Long09Y-199 included carbon fixation in photosynthetic organisms,flavonoid biosynthesis,arginine and proline metabolism,fatty acid biosynthesis,citric acid cycle（TCA cycle）,glycolysis/glucone Generation and ABC transporters.Pathways only significantly enriched in Hu 90-6573 included isoquinoline alkaloid biosynthesis,nitrogen metabolism,indole alkaloid biosynthesis,and betaine biosynthesis.In the clustering and expression trend analysis of DEGs on Long 09Y-199 and Hu90-6573 at different stages of development,two gene modules with a total of 1128 genes in the experimental group were screened as up-regulated and the expression level increased with the prolongation of processing time.This study conducted KEGG analysis on these differential genes and screened 3 significantly enriched pathways,namely phenylpropane metabolism,starch and sucrose metabolism,and MAPK signaling pathway-plant.2Alanine lyase genes,4 shikimate o-hydroxycinnamoyl transferase genes and 21peroxidase-related genes were up-regulated in phenylpropane metabolism pathway;3β-fructofuranosidase genes,1α-amylase gene and 6β-glucosidase genes were up-regulated in starch and sucrose metabolism pathway;1 protein node MKK2 gene,3abscisic acid PYR/PYL protein genes,11 protein node related genes（i.e.PP2C gene,Sn RK2 gene,MAPKKK17＿18 gene and CAT1 gene）were up-regulated in MAPK signaling pathway-plant.