Differential behavior of the antioxidant system in response to salinity induced oxidative stress in salt-tolerant and salt-sensitive cultivars of Brassica juncea L

In the present study, the ability of salt tolerant (CS-52) and salt sensitive (RH-8113) cultivars of Brassica juncea L. was investigated for their differential antioxidant defense mechanism to counter the salinity induced oxidative stress. The seedlings were treated with varying levels of NaCl (0, 50, 100 and 150 mM) and changes in content of malondialdehyde (MDA), hydrogen peroxide (H2O2), ascorbic acid, glutathione and proline were examined. Further, salinity induced variations in activity levels of leaf superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APOX), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) in both the cultivars were also investigated. Production of H2O2 and MDA was much higher in salt sensitive cultivar RH-8113. Glutathione, ascorbic acid and proline content enhanced in both the cultivars with more pronounced effect on tolerant cultivar CS-52. The salt tolerant cultivar CS-52 exhibited significant increase in the activities of SOD, DHAR and GR in response to the increasing salinity, though no increase in the activity of CAT, POX and APOX was observed. However, basal level of POX and APOX was found to be much higher in the salt tolerant cultivar CS-52. In comparison, SOD activity declined and that of CAT, DHAR and GR remained unaltered in salt sensitive cultivar RH-8113, though there was significant increase in the activities of POX and APOX. These results suggest that cultivar CS-52 exhibit better protective mechanism against salt induced oxidative damage by maintaining higher levels of antioxidant enzymes and of some antioxidants in comparison to salt sensitive cultivar RH-8113.