Abstract: To explore the physiological mechanism of exogenous brassinosteroids (BRs) regulating salt tolerance of alfalfa seedling, the seedlings of M. sativa cv. Zhongmu No.3 and M. sativa cv. Longzhong were selected as the experimental materials, water culture with nutrient solution was used, under 150 mmol/L NaCl stress, the leaves were sprayed with 0.1 μmol/L exogenous 2,4-epibrassinolide (EBR), the effects of exogenous EBR on plant height, aboveground biomass, osmoregulation and antioxidant capacity of alfalfa seedlings under NaCl stress were studied. The results showed that:under 150 mmol/L NaCl stress, the seedling height and aboveground biomass of Zhongmu No.3 and Longzhong decreased significantly, the content of soluble protein and CAT activity in leaves decreased significantly, active oxygen (O₂^-·, OH^·, H₂O₂) accumulated in large quantities, MDA content of membrane lipid peroxidation products increased significantly. Under 150 mmol/L NaCl stress, after spraying 0.1 μmol/L exogenous EBR, the seedling plant height of Longzhong and the seedling aboveground biomass of Zhongmu No.3 increased significantly,the content of soluble protein in the leaves of Longzhong alfalfa and Zhongmu No.3 alfalfa seedlings increased significantly, the content of soluble protein in leaves increased significantly, the activities of SOD, GPX, APX, GR, CAT and GSH, AsA increased significantly, the production of active oxygen (O₂^-·, OH^·, H₂O₂) decreased significantly, and the degree of membrane lipid peroxidation decreased significantly. The results showed that under NaCl stress, the application of exogenous EBR could enhance the osmotic regulation ability of alfalfa seedlings, increased the activities of enzymatic antioxidant system and non enzymatic antioxidant system of alfalfa seedlings, and inhibit the accumulation of active oxygen in alfalfa seedlings. All above resulted in the reduction of osmotic stress and oxidative damage caused by NaCl stress on alfalfa seedlings, and the significant promotion of alfalfa seedlings growth, which having a positive effect on improving salt resistance of alfalfa seedling.

Key words: Medicago sativa, 2,4-epibrassinolide, NaCl stress, Osmotic adjustment, Antioxidant system

CLC Number: 

• S634.3