Difference In Salt Tolerance And Photosynthetic Physiological Response Of Elytrigia Repens Under Salt Stress

In this study,42 germplasms of Elytrigia repens were used as experimental materials.Chromosome ploidy identification was performed by flow cytometry combined with conventional tabletting method;The salt damage score,relative electrolytic conductivity,chlorophyll,Na+/K+,stem dry weight,root dry weight and root-shoot ratio of 42 genetypes of E.repens were measured during the seedling stage with hydroponic experiment under 0 mmol/L and 200 mmol/L NaCl stress,and based on the salt tolerance coefficient of each index,the salt tolerance of E.repens germplasm was comprehensively evaluated by principal component analysis,membership function analysis and cluster analysis.The key indexes for distinguishing the salt tolerance of E.repens were obtained by multiple stepwise regression analysis,and the salt tolerance prediction model was constructed.;On this basis,the photosynthetic parameters and physiological indicators of 0,1,3,6,and 10 days were determined by using salt-tolerant genetype E42 and salt-sensitive genetype E23 under 0 and 200 mmol/L NaCl at seedling stage,and at the same time the leaves were taken for realtime fluorescence quantitative relative expression analysis of key photosynthetic genes.Through the above studies,the aim is to enrich the research on chromosome ploidy of E.repens,to provide key indicators and evaluation methods for the screening salt-tolerant germplasm of E.repens and to initially clarify the salttolerance photosynthetic physiology and molecular response mechanism of E.repens,and provide a basis for salt-tolerance breeding and gene cloning of E.repens.The main findings are as follows:(1)The chromosome ploidy of the tested E.repens germplasm was hexaploid with flow cytometry,the mean fluorescence value was 142.06,and the coefficient of variation ranged from 2.33%to 5.00%.E2,E6,and E23 were ploided by conventional tabletting,the number of chromosomes was 42.The identification was consistent with the results obtained by flow cytometry.(2)The results of salt tolerance identification for 42 E.repens germplasms by hydroponics method showed,compared with the control,the score of salt damage,relative electrolytic conductivity,Na+/K+increased,chlorophyll content,stem and root dry weight decreased.The comprehensive evaluation of salt tolerance of the tested germplasms was from 0.273 to 0.862 by membership function analysis.The smaller D value of E10,E36,and E23 materials indicated weaker salt resistance,and the larger D values of E34,E40,and E42 indicated stronger salt resistance.Germplasms could be divide into 4 categories by cluster analysis.Salt tolerance prediction of E.repens regression model was established by stepwise regression method during seedling period,and it was D=0.05-0.04X1-0.003X2+0.341X3+0.234X4+0.075X5,X1 is the salt damage score,X2 is relative electrolytic conductivity,X3 is chlorophyll,X4 is root dry weight,and X5 is root-shoot ratio,as were key indexes for salt tolerance evaluation of E.repens.(3)Under salt stress,the reason that the salt tolerance of E42 was higher than that of E23 might be due to the higher ability to transport K+upwards to maintain higher K+/Na+ of the leaves;maintaining higher SOD,POD,CAT activity for a longer period of time to reduce plasma membrane damage;maintaining a high PEPC activity to get a high photochemical efficiency under the stomatal CO2 concentration was limited in the later stage to ensure the growth of E42.For gene expression,the chloroplast gene c187308.graph-c0 continuously increased,and the gene expression level of E42 is higher than that of E23,indicating this gene might be related to salt tolerance of E.repens.