Improved salt tolerance by α-tocopherol in soybean involves up-regulation of ascorbate-glutathione cycle and secondary metabolites

The effects of alpha-tocopherol on growth, photosynthesis, oxidative parameters, and tolerance mechanisms in soybean under increased salinity were studied. Salinity stress reduced shoot length, dry weight, chlorophyll and carotenoids, photosynthesis, and PSII activity; however, alpha-tocopherol mitigated the decline considerably. Salinity stress caused accumulation of superoxide (O-2(-center dot)) hydrogen peroxide (H2O2), thereby increased lipid peroxidation and decreased membrane stability index. Application of alpha-tocopherol ameliorated oxidative damage by reducing lipid peroxidation and downregulating lipoxygenase activity. The up-regulation of antioxidant and glyoxylase systems protected soybean from the damaging effects of ROS and methylglyoxal. Moreover the content of ascorbate, reduced glutathione and alpha-tocopherol increased significantly. The activity of gamma-glutamyl kinase also increased due to application of alpha-tocopherol and accumulation of Na+ was significantly declined with enhancement in K+ uptake. Therefore results of present study revealed the beneficial effect of foliar application of alpha-tocopherol under salinity stress in soybean.