Cadmium stress resistance of Medicago sativa L. based on correlation analysis and principal component analysis

【Objective】The purpose of the study was to explore the changes of physiological and biochemical indexes of Medicago sativa L.seedlings under cadmium (Cd) stress,to screen out the typical index factors,and to provide a theo-retical basis for phytoremediation of Cd pollution in soil.【Method】M.sativa seeds were cultured after stress treatments with different Cd concentrations (0,1,5,10,15,30 and 50 mg/L),and the physiological indexes of the seedlings were determined.Correlation analysis and principal component analysis were used to analyze each index,and the effects of Cd stress on the physiological status of M.sativa were evaluated.【Result】With the increase of Cd concentration,the root cell vitality,chlorophyll and soluble protein contents of M.sativa cotyledons gradually decreased,while the contents of malondialdehyde (MDA),hydroxyl radical(·OH) and superoxide anion radical (O₂^-·)in cotyledons gradually increased,and the contents of Cd in seedlings,proline content,soluble sugar content,hydrogen peroxide (H₂O₂) content,superoxide dismutase (SOD) activity,catalase (POD) activity and catalase (CAT) activity in cotyledons showed a tendency of in-creasing and decreasing.When the concentration of Cd was 1 mg/L,the SOD activity reached the maximum value of 320U/mg.When the concentration of Cd was 5 mg/L,the soluble sugar content reached the maximum value of 11.276µg/g.When the concentration of Cd was 10 mg/L,proline content and CAT activity reached the maximum value of 80.147µg/g and 77 U/(g·min) respectively.H₂O₂ content,POD activity and Cd content reached the peak at a Cd concentration of 30mg/L,which were 15.75μmol/g,1412 U/(g·min) and 2.135 mg/g respectively.The results of correlation analysis showed that Cd concentration was extremely significantly positively correlated with the contents of·OH,O₂^-·and MDA contents in M.sativa cotyledons and Cd content in the whole seedling (P<0.01,the same below),and extremely signifi-cantly negatively correlated with the contents of chlorophyll a,chlorophyll b,total chlorophyll,soluble protein and soluble sugar,as well as with CAT activity and root cell vitality.The results of principal component analysis showed that the cumulative contribution rate of the first principal component (PC1) and the second principal component (PC2) was87.50%,the root cell vitality had the highest loading in PC1,and the soluble sugar content had the highest loading in PC2.【Conclusion】M.sativa has a certain enrichment effect on Cd in the external environment,which can be considered as one of the plants to repair Cd-polluted areas,and the root cell vitality and soluble sugar content can be used as impor-tant indexes to evaluate the effect of Cd stress on M.sativa.