Tocopherol confers water stress tolerance: Sugar and osmoprotectant metabolism in mung bean [Vigna radiata (L.) Wilczek]

The effective contribution of alpha-tocopherol (alpha-Toc) in drought stress tolerance was assessed in mung bean plants. Two mung bean cultivars (Cyclone 7008 and Cyclone 8009) were grown under non-stress (100% field capacity) and water stress (60% field capacity) conditions. Along with control (no spray), three levels of alpha-Toc (100, 200 and 300 mg L-1) were applied as foliar spray to mung bean plants at the vegetative growth stage. Exogcnously applied alpha-Toc significantly improved plant growth, chlorophyll b, relative water content, glycinebetaine (GB), reducing sugars, total soluble sugars, transpiration rate (E), stomatal conductance (g(s)), sub-stomatal CO2 concentration (C-i), and C/C-a under well-watered and water deficit conditions. However, cv. Cyclone 7008 was significantly better in reducing and non-reducing sugars, while cv. Cyclone 8009 in leaf proline concentration. Overall, exogenously applied alpha-Toc - in particular 300 mg L-1 - was effective in improving plant growth of both mung bean cultivars, which was found to be associated with alpha-Toe-induced increase in E, g(s), C-i, GB, proline and sugar contents.