Studies on effect of exogenous application of ascorbic acid on growth, photosynthetic pigment and oxidative defence in ‘groundnut’ (Arachis hypogaea L.) under lead (Pb) stress

Seed priming with various chemicals enhances plant resistance to different environmental stresses. While extensive research highlights the benefits of priming under various stressful conditions, limited studies have explored the role of ascorbic acid (AsA) in inducing lead (Pb) stress tolerance through seed priming. This study aims to assess the impact of AsA priming on the physiological and biochemical responses of groundnut plants under Pb stress. In the present study, we used a lead (Pb) concentration of 100 mg L⁻1 to induce stress. For seed priming, the seeds were soaked for 24 h in distilled water (hydropriming) or in two different concentrations of AsA (50 and 100 mg L⁻1). We found that exposure to Pb stress led to a notable decrease in plant growth and photosynthetic pigments, as well as a reduction in total carbohydrate levels. In contrast, the levels of free proline, total soluble proteins, and AsA increased in response to Pb stress. A notable increase in the activities of peroxidase (POD), superoxide dismutase (SOD), and polyphenol oxidase (PPO) was recorded in response to lead (Pb) stress treatment. Concurrently, heightened levels of malondialdehyde (MDA) and hydrogen peroxide (H2O2) were also observed under Pb stress conditions, suggesting the onset of oxidative stress. Nevertheless, our observations revealed that seeds primed with ascorbic acid (AsA) exhibited enhanced performance across various parameters including growth, photosynthetic efficiency, and the concentration of essential biomolecules. Priming groundnut seeds with 50 mg L⁻1 of ascorbic acid (AsA) significantly improved their ability to withstand lead (Pb) stress. This was reflected in enhanced plant growth, as seen in increased fresh and dry biomass of shoots, along with greater shoot lengths and photosynthetic pigments. These findings suggest that AsA priming can be an effective strategy to mitigate Pb-induced stress and promote healthier plant development.