Role of selenium in preventing manganese toxicity in sunflower (Helianthus annuus) seedling

• Characterize the toxic mechanism associated with Mn exposure in sunflower seedlings.
• Illustrates the antioxidant properties of Se against Mn toxicity.

In addition to various metabolic disorders, one of the consequences of manganese (Mn) toxicity is oxidative stress in plant species. The aim of this study was to evaluate the toxic mechanism associated with Mn exposure and to investigate the possible mediatory role of Se in protecting plants from Mn toxicity. The exposure of sunflower (Helianthus annuus) seedlings to 100 μM Mn inhibited biomass production, decreased chlorophyll (Chl) and carotenoids (Cars) contents and intensively increased the accumulation of Mn in both roots and shoots. Concomitantly, Mn application enhanced hydrogen peroxide (H2O2), protein carbonyl (PCO) content and lipid peroxidation as indicated by malondialdehyde (MDA) accumulation. Presoaking seeds with Se (5, 10 and 20 μM) alleviated the negative effect of Mn on plant growth parameters and led to a significant increase of Chl and Cars contents. Furthermore, Se application mitigated the oxidative damages as evidenced by the lowered H2O2, PCO and MDA contents and led to a decrease in oxidative injuries caused by Mn toxicity. Se particularly induced an increase in catalase (CAT), ascorbate peroxidase (APX) and glutathione peroxidase (GPX) activities accompanied by a significant reduction in SOD activities. Our study provides evidence that Se alleviated the Mn-induced oxidative stress in sunflower seedlings by enhancing the antioxidant defense system.