Changes in antioxidant activity in sub-cellular fractions of tolerant and susceptible wheat genotypes in response to long term salt stress

Effects of long term, medium level (electrical conductivity of extract (ECe) = 6.85 dS m(-1)) sodium chloride (NaCl) salinity were studied in tolerant (Kharchia 65) and susceptible (HD 2687) wheat genotypes. NaCl salinity caused decrease in relative water content (RWC), chlorophyll (CHL), membrane stability index (MSI) and ascorbic acid (AA) content, and increased the contents of hydrogen peroxide (H2O2), thiobarbituric acid reactive substances (TBARS) (measure of lipid peroxidation) and activities of superoxide dismutase (SOD), its various isozymes, ascorbate peroxidase (APOX) and glutathione reductase (GR) in wheat genotypes Kharchia 65 (tolerant) and HD 2687 (susceptible). Salinity tolerant wheat cv. Kharchia 65 showed less decline in RWC, CHL, MSI estimated in whole tissue than salt sensitive HD2687. Kharchia 65 also exhibited less decrease in AA content, less increase in H2O2, TBARS contents and higher increase in SOD and its isozymes, APOX and GR in all sub-cellular fractions than salt sensitive HD 2687. H2O2, TBARS contents and AA contents were higher in chloroplastic fraction. Chloroplastic fraction showed higher total SOD, APOX and GR activity, followed by mitochondrial fraction in case of total SOD and GR, while cytosolic fraction was in second place in case of APOX activity. Though Mn-SOD activity was highest in mitochondrial fraction, but residual activity was also observed in cytosolic fraction. Cu/Zn-SOD and Fe-SOD were observed in all the sub-cellular fractions, however, the activities were higher in chloroplastic fraction for both the isoforms. Total Cu/Zn-SOD activity, sum of activity observed in all the fractions, was higher than other SOD isoforms. Susceptibility of HD 2687 to long-term salinity stress seems to be due to relatively less induction of SOD isozymes, no induction in chloroplastic and mitochondrial APOX and cytosolic GR and decrease in chloroplastic GR under salt stress resulting in higher oxidative stress in the form of H2O2 and TBARS contents and decrease in MSI and CHL. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.