Strigolactone Mitigates Nickel Toxicity by Regulating Nutrient Uptake, Antioxidant Defense, Vitamins and Phytohormones Biosynthesis in Pepper Seedlings

Abstract

Here, pepper plants were subjected to non-stress control, control with strigolactone (SL), Nickel (Ni)-stress and Ni+ SL conditions to investigate the morpho-physiological and biochemical alterations in plant. Excess Ni produced significant negative impacts on plant's morphology, essential nutrients, and phytohormones content as compared to control plants. However, it caused tremendous increment of hydrogen peroxide (H2O2), and malondialdehyde (MDA) and the effects were further triggered by increasing concentration. Consistently, Ni induced the activity of enzymatic antioxidants like superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) compared to control plants. It also showed downregulation of photosystem II (PSII)-related CaPsb2, aquaporin-related CaPIP1-1 and CaPIP1-2, and dehydrin-related CaDHN3 transcripts. Exogenous SL improved plant's phenotypes in control plants and greatly repaired the morphology of Ni-stressed plants. Although, sucrose accumulation was greatly enhanced by SL in Ni-stressed plants, proline content was only heightened under 500 mu M Ni. SL showed tremendous enhancement of nutrients and phytohormones in control plant and caused significant restoration of those in Ni-stressed plant. However, SL significantly reduced reactive oxygen species (ROS) in the Ni-stressed plants. This reduction correlated with elevated levels of both non-enzymatic and enzymatic antioxidants, despite the decline observed in CAT activity under extreme Ni-stressed condition. SL also showed modulation of CaPsbD transcript under Ni stress. Taken together, SL (20 mu M) produced the best results in improving most of parameters studied here, as evidenced by our multivariate analysis. The findings claim the crucial role of exogenous SL in growth and mitigation of Ni-toxicity in pepper.