Salt-Induced Changes in Physio-Biochemical and Antioxidant Defense System in Mustard Genotypes

Salinity stress is a major factor limiting plant growth and productivityof many crops including oilseed. The present study investigated the identificationof salt tolerant mustard genotypes and better understanding the mechanism of salinity tolerance. Salt stresses significantly reduced relative water content (RWC),chlorophyll (Chl) content, K⁺ and K⁺/Na⁺ ratio, photosynthetic rate (P_N), transpiration rate (Tr), stomatal conductance (gs), intercellular CO₂ concentration(Ci) and increased the levels of proline (Pro) and lipid peroxidation (MDA) contents, Na⁺, superoxide (O₂^•−) and hydrogen peroxide (H₂O₂) in both tolerant andsensitive mustard genotypes. The tolerant genotypes maintained higher Pro andlower MDA content than the salt sensitive genotypes under stress condition.The activities of superoxide dismutase (SOD), catalase (CAT), peroxidase(POD), glutathione peroxidase (GPX), monodehydroascorbate reductase(MDHAR) and dehydroascorbate reductase (DHAR) were increased with increasing salinity in salt tolerant genotypes, BJ-1603, BARI Sarisha-11 and BARISarisha-16, but the activities were unchanged in salt sensitive genotype, BARISarisha-14. Besides, the increment of ascorbate peroxidase (APX) activity washigher in salt sensitive genotype as compared to tolerant ones. However, the activities of glutathione reductase (GR) and glutathione S-transferase (GST) wereincreased sharply at stress conditions in tolerant genotypes as compared to sensitive genotype. Higher accumulation of Pro along with improved physiologicaland biochemical parameters as well as reduced oxidative damage by up-regulationof antioxidant defense system are the mechanisms of salt tolerance in selectedmustard genotypes, BJ-1603 and BARI Sarisha-16.