Mitigating Salinity-Induced Oxidative Stress Involves Enhanced Expression of the Antioxidant System in a Salt-Tolerant Variety of Brassica juncea L.

Salinity is a major abiotic stress that disrupts redox homeostasis, leading to oxidative damage in plants. This study comparatively evaluated the oxidative stress responses of salt-sensitive (Brassica juncea cv. RH-8113) and salt-tolerant (cv. CS-52) cultivars under varying NaCl concentrations, with a focus on lipid peroxidation, reactive oxygen species (ROS) accumulation, and antioxidative defense mechanisms. Plants were subjected to increasing NaCl concentrations (0–150 mM). Biochemical assays were conducted to quantify malondialdehyde (MDA), hydrogen peroxide (H2O2), non-enzymatic antioxidants (ascorbate, glutathione, proline), and enzymatic antioxidants (SOD, CAT, POX) in root tissues. MDA content increased in both cultivars under salt stress; however, absolute MDA levels remained consistently higher in RH-8113. At 150 mM NaCl, MDA increased by 90% in CS-52 and 57% in RH-8113 over respective controls. H2O2 levels rose by 78% in RH-8113 and 56% in CS-52. Ascorbate content increased by 187% in RH-8113 and 97% in CS-52, yet CS-52 maintained higher basal and stress-induced levels. Glutathione content rose by 68% in CS-52 and 46% in RH-8113. Proline accumulation was significantly higher in CS-52 (97%) compared to RH-8113 (70%) at 150 mM NaCl. SOD activity increased by 74 and 84% in CS-52 and RH-8113, respectively, with CS-52 displaying threefold higher basal activity. CAT activity declined in both cultivars, with a 77% reduction in CS-52 and 50% in RH-8113. POX activity increased threefold in CS-52 and twofold in RH-8113 under maximum salinity. The salt-tolerant cultivar CS-52 demonstrates superior oxidative stress tolerance via higher basal and inducible levels of non-enzymatic (ascorbate, glutathione, proline) and enzymatic (SOD, POX) antioxidants, coupled with lower ROS and lipid peroxidation levels. These findings underscore the robust redox buffering capacity of CS-52, making it a promising candidate for breeding salt-resilient Brassica genotypes.