Role of glycine betaine in mitigating salt-induced oxidative stress in Vigna radiata

The impact of exogenously applied glycine betaine (GB; 0, 5, 10, 20 and 50 mmol) was evaluated in preventing <i>Vigna radiata</i> from the adverse effects of salt (100 mmol NaCl) stress. Salinity reduced growth parameters, such as plant height and fresh and dry weight of plants, while GB application significantly alleviated the decline. Salinity stress led to a decline in total chlorophylls and carotenoids, as well as a reduction in the net photosynthetic rate and gas exchange attributes, including stomatal conductance, transpiration rate, and intercellular CO₂. However, GB supplementation significantly alleviated this decline. Salinity stress increased the accumulation of hydrogen peroxide, superoxide and methylglyoxal, while as applied GB reduced their accumulation, causing a significant decline in the lipid peroxidation. Application of GB, at all concentrations, increased the activity of the antioxidant enzymes under normal and salinity stress treatments with 10 and 20 mmol concentrations, imparting the highest increase. Increase in the radical scavenging activity due to GB application was also supported by increased total antioxidant activity assays measured as percent DPPH and ABTS radical scavenging. In addition, GB-supplemented plants exhibited an apparent increase in the activities of glyoxalase I and glyoxalase II enzymes. Accumulation of osmotic compounds like proline, sugars and GB increased significantly due to GB application and showed a further increase in salt-stressed plants. More importantly, the GB-treated plants exhibited a considerable decline in sodium accumulation, causing a decline Na/K in them. Glycine betaine was effective in mitigating the deleterious effects of salinity.