Hydrogen sulfide regulates the levels of key metabolites and antioxidant defense system to counteract oxidative stress in pepper (Capsicum annuum L.) plants exposed to high zinc regime.

In the present experiment, we aimed to test the impact of hydrogen sulfide (H2S) on growth, key oxidant such as hydrogen peroxide, mineral elements, and antioxidative defense in Capia-type red sweet pepper (Capsicum annuum L.) plants subjected to high concentration of zinc (Zn). A factorial experiment was designed with two Zn levels (0.05 and 0.5 mM) and 0.2 mM sodium hydrosulfide (NaHS) as a donor of H2S supplied in combination plus nutrient solution through the root zone. High level of Zn led to reduce dry mass, chlorophyll pigments, fruit yield, leaf maximum fluorescence, and relative water content, but enhanced endogenous hydrogen peroxide (H2O2), free proline, malondialdehyde (MDA), electrolyte leakage (EL), H2S, as well as the activities of peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) enzymes. Exogenously applied NaHS significantly enhanced plant growth, fruit yield, water status, the levels of H2S and proline as well as the activities of different antioxidant enzymes, while it significantly suppressed EL, MDA, and H2O2 contents in the pepper plants receiving low level Zn. NaHS application to the control plants did not significantly change all these parameters tested except the dry matter which increased significantly. High Zn regime led to increase intrinsic Zn levels in the leaves and roots, but it lowered leaf nitrogen (N), phosphorus (P), and iron (Fe) concentrations. However, NaHS reduces the Zn conc. and enhances Fe and N in leaf and root organs. It can be concluded that NaHS can mitigate the harmful effects of Zn on plant growth particularly by lowering the concentrations of H2O2, Zn, EL, and MDA, and enhancing the activities of enzymatic antioxidants and levels of essential nutrients in pepper plants.