Physiological and biochemical characteristics of Vigna species for Al stress tolerance

The objective of the present investigation was to evaluate Al tolerance in three Vigna species viz. V. radiata (‘Pusa-672’), V. mungo (‘Mash-114’) and V. umbellata (‘RBL-6’) under Al stress conditions. All three Vigna species were assessed in hydroponic assay in various concentration of Al (0, 74 and 185 μM) for 48 h. Variations in the Al tolerance were analysed based on various traits such as root elongation rate, re-growth after hematoxylin staining, accumulation of aluminium and callose and their localization, H2O2, lipid peroxidation and antioxidant enzymes activity. Aluminium stress caused inhibition in root elongation rate and root re-growth and increased accumulation of aluminium, callose, H2O2 and lipid peroxidation in all three Vigna species. However, accumulation of aluminium, callose, H2O2 and lipid peroxidation was more in V. radiata (‘Pusa-672’) than in V. mungo (‘Mash-114’) and V. umbellata (‘RBL-6’). Higher activity of superoxide dismutase (SOD; EC 1.15.1.1), guaiacol peroxidase (GPX; EC 1.11.1.7) and ascorbate peroxidase (APX; EC 1.11.1.11) was observed in V. umbellata than in V. mungo and V. radiata. Transverse sections of roots were examined to confirm the localization of Al in the apoplastic or symplastic regions using fluorescent microscopy. In V. umbellata (‘RBL-6’) and V. mungo (‘Mash-114’), most of the Al was localised in the epidermal and cortical tissues indicating restricted movement of Al to the upper layers. In V. radiata, (‘Pusa-672’) more Al was localised in epidermal, cortical, and even endodermal tissues, suggesting its inability to restrict the Al in upper layers. Our findings suggest that V. umbellata as a potential genetic resource for Al tolerance and this trait can be introgressed through breeding programme to develop Al-tolerant genotypes in V. mungo and V. radiata.