ORIGINAL ARTICLE

Lead-induced Oxidative Stress and Redox Homeostasis in Soybean

A controlled pot experiment was conducted to evaluate the effects of graded concentrations of lead acetate (Pb (CH₃COO)₂.3H₂O) on the antioxidant defense system of soybean (Glycine max L.). Soil was amended with lead at 0 (control), 200, 400, 600, 800, and 1000 mg kg⁻¹, and enzymatic responses were assessed at pre-flowering (30 days), peak-flowering (45 days), and post-flowering (60 days) stages under triplicate conditions. A significant enhancement in antioxidant enzyme activities was observed with increasing lead concentration up to 800 mg kg⁻¹. Maximum activities of catalase (6.037, 6.895, and 6.915 mM), peroxidase (2.814, 3.922, and 4.532 mM), superoxide dismutase (3.42, 3.95, and 5.39 U g⁻¹ ), glutathione reductase (2.9242, 4.3174, and 5.6712 mM), and ascorbate peroxidase (6.8432, 7.6152, and 6.9636 mM) were recorded at pre-, peak-, and post-flowering stages, respectively, at 800 mg kg⁻¹. However, a further increase to 1000 mg kg⁻¹ resulted in a decline in enzyme activities, indicating the onset of lead-induced toxicity. The results highlight that moderate lead enrichment stimulates the plant antioxidant machinery, enhancing tolerance against oxidative stress. Superoxide dismutase plays a pivotal role in dismutating superoxide radicals into H₂O₂, which is subsequently detoxified by catalase, peroxidase, and ascorbate peroxidase, thereby maintaining cellular redox homeostasis. These findings emphasize the need for careful management of lead levels in agricultural soils to prevent toxicity while optimizing soybean productivity.