Effect of La(NO₃)₃ on seedling growth and physiological characteristics of ryegrass under NaCl stress

To explore the alleviation effect of rare earth La on salt stress damage in herbages, the effects of 20 mg·L^-1 La(NO₃)₃ foliar spraying on seedling growth and physiological characteristics of ryegrass (Lolium perenne L.) under NaCl stress were investigated in a hydroponic culture experiment. The results indicated that salt stress significantly inhibited plant growth, but enhanced leaf electrolytic leakage and MDA, O₂^- and H₂O₂ contents in ryegrass seedlings. The intensities of the above effects increased with increasing NaCl concentrations. With the increasing NaCl concentration, the activities of SOD, CAT and APX, and the contents of AsA, GSH, soluble protein and proline in seedling leaf initially increased before decreasing afterwards. Furthermore, soluble sugar and Na⁺/K⁺ ratio increased and plasma membrane H⁺-ATPase activity steadily decreased. NaCl stress meantime increased leaf POD activity and isoperoxidase expression in ryegrass seedlings. Compared with NaCl stress treatment, spraying La(NO₃)₃ under NaCl stress decreased accumulation of O₂^- and H₂O₂, and improved activities of SOD, CAT, POD, APX and H⁺-ATPase of plasma membrane, and isoperoxidase expression in ryegrass leaf. It also significantly enhanced AsA, GSH, soluble protein, soluble sugar, free proline and biomass, while limiting Na⁺/K⁺ ratio. The above results suggested that La(NO₃)₃ alleviated oxidative damage and growth inhibition due to NaCl stress in ryegrass seedlings. It increased antioxidant activity and osmoticum content, and therefore improved NaCl resistance in ryegrass plants.