Alleviating effect of nitric oxide on oxidative stress and antioxidant defence system in pepper (Capsicum annuum L.) plants exposed to cadmium and lead toxicity applied separately or in combination

Abstract The study aimed at examining the potential of exogenous application of sodium nitroprusside (SNP; 0.1 mM), a nitric oxide (NO) donor, on some growth characteristics, organic metabolites/biomolecules and mineral nutrients of pepper plants subjected to cadmium (Cd) and lead (Pb) stresses (0.1 mM PbCl 2 and 0.1 mM CdCl 2 ) imposed separately or in combination. The detrimental effects of combined application of Cd and Pb were more striking than those when applied singly on dry mass, efficiency of photosystem II ( F v/ F m), chlorophyll content, leaf relative water content, electrolyte leakage (EL), hydrogen peroxide (H 2 O 2 ), malondialdehyde (MDA), proline coupled with a rise in activities of leaf key enzymatic antioxidants including peroxidase, superoxide dismutase, catalase and lipoxygenase, and the levels of non-enzymatic antioxidants ascorbate and glutathione. NO treatment effectively enhanced key growth attributes, while it decreased EL, proline, MDA and H 2 O 2 as well as the activities of antioxidant enzymes in plants grown at an individual stress than those grown under combined stresses. Addition of both metals to the nutrient solution increased tissue Cd and Pb levels, but it lowered down Ca and K. However, SNP treatment reversed the levels of all these metals/nutrients. Overall, SNP is beneficial to alleviate the deleterious effects of Cd and Pb on pepper plants.