Reactive oxygen species (ROS) play a critical role in developmental and signal transduction processes during seed germination and early seedling establishment stages. Higher concentrations of ROS are known to have detrimental effects when the plant is under salt stress. In the present study, we aimed to test the early (1 h) and late (48 h) response of enzyme-driven ROS detoxification system in six peanut genotypes under salt stress at early seedling stage. Salt stress was imposed with three treatment concentrations of NaCl (50, 100 and 200 mM NaCl), all of which showed a reduction in seed germination and seedling vigour index. The 200 mM NaCl stress showed severe reduction of growth, while 100 mM NaCl stress resulted in rapid increase in O₂˙⁻ and H₂O₂ contents. The O₂˙⁻ content increased twofold in sensitive genotypes after 1 h of stress, whereas the tolerant genotypes showed ~ 60% rise. A prompt rise (> 50-fold) in SOD transcript was occurred within 1 h of salt stress in the tolerant genotypes (early response). But induction in SOD activity was observed only after 48 h of salt stress (late response). After 48 h of salt stress, the tolerant genotypes showed greater induction of POD activity, whereas in the sensitive genotypes CAT activity was more pronounced. We found POD and CAT played a greater role in H₂O₂ detoxification in tolerant and sensitive genotypes, respectively, during longer duration of the stress. This study summarizes the selective induction of different components of antioxidant enzyme system and their role in cellular fine tuning of ROS level in peanut under salt stress during seedling establishment stage.
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