Efficacy of ascorbate-glutathione cycle for scavenging H2O2 in two contrasting rice genotypes during salinity stress

Abstract

Twenty day-old seedling of Pokkali (salt-tolerant) and BRRI dhan 29 (salt-sensitive) rice genotypes were exposed to 0, 75 and 150 mM NaCl salinity levels for 7 days to investigate the efficacy of ascorbate-glutathione cycle for scavenging H2O2 during salinity stress. Results revealed that salinity caused a significant decrease in photosynthesis rate (A), stomatal conductance (gs), chlorophyll content and shoot dry matter yield, with a greater reduction in the sensitive genotype, BRRI dhan 29. The activity of SOD (super oxide dismutase), an H2O2 generating enzyme increased significantly due to salinity in both the rice genotypes. Pokkali exhibited increased activities of Fe-SOD and Cu/Zn-SOD while Mn-SOD was in BRRI dhan 29. With increasing salinity levels, H2O2 and Thiobarbituric acid reactive substances (TBARS) content were increased significantly in both the genotypes with a higher magnitude in BRRI dhan 29. Both rice genotypes exhibited an increased activity of Peroxidase (POD) and a decreased activity of Catalase (CAT). The salt-tolerant genotype, Pokkali exhibited increased activity of ASC-GSH cycle enzymes (APX, MDHAR, DHAR and GR) during salinity stress. But salt-sensitive, BRRI dhan 29 exhibited a significant decreased activity of APX, increased activity of DHAR and unchanged activity of Monodehydroascorbate reductase (MDHAR) and GR during salinity stress. The results clearly indicated that ASC-GSH cycle responded differentially in salt-tolerant and salt-sensitive rice genotypes during salinity stress.