Differential effect of salinity on thermotolerance of SOD isoforms in seven varieties of Vigna mungo (L.) Hepper

Seven varieties of Vigna mungo, collected from different geographical regions of India, were chosen for a comparative analysis of SOD isoenzyme profiles under salt stress, and to determine if prior exposure of the seedlings to salt stress resulted in any alteration in thermotolerance of the SOD isoforms. Three SOD isoforms Mn-SOD, Fe-SOD and Cu/Zn-SOD were present in both leaves and roots of all the varieties. Fe-SOD and Cu/Zn-SOD were most predominant in leaves whereas the roots predominantly had Fe-SOD. Mn-SOD was least abundant in leaves, while it was the second most abundant SOD isoform in roots. Salt-induced changes in SOD isoform profiles were not uniform either in leaves or roots. Cu/Zn-SOD was found to be more responsive to salinity than the other SOD isoforms in both tissues. Prior exposure of seedlings to salt stress resulted in increase in thermotolerance of Cu/Zn-SOD in leaves of IPU-2-43, Shekhar-2, Azad-2 and UH-1 and roots of IPU-2-43 and Shekhar-2 varieties. The UH-1 variety appeared unique as it possessed an additional Cu/Zn-SOD isoform in roots, which was induced by salt as well as heat. This variety also exhibited a new Fe-SOD band which was heat-induced in roots of seedlings that were not exposed to salt, but disappeared in roots which were salt stressed prior to heat exposure. Hence, the seven varieties exhibited diversity in behavior with respect to SOD activities under salinity and high temperature.