Silicon is dependent on hydrogen sulphide to improve boron toxicity tolerance in pepper plants by regulating the AsA-GSH cycle and glyoxalase system

Abstract

The role of endogenous hydrogen sulphide (H₂S) in silicon-induced improvement in boron toxicity (BT) tolerance in pepper plants was studied. Two-week old seedlings were subjected to control (0.05 mM B) or 2.0 mM BT in a nutrient solution. These two treatments were combined with 2.0 mM Si. BT caused considerable reduction in biomass, chlorophyll a &b, photosystem II maximum quantum efficiency (Fv/Fm), glutathione and ascorbate in the pepper seedlings. However, it enhanced malondialdehyde (MDA) and hydrogen peroxide, electrolyte leakage, proline, H₂S, and activities of catalase, superoxide dismutase, peroxidase, and L-DES. Silicon stimulated growth, proline content and activities of various antioxidant biomolecules and enzymes, leaf Ca²⁺, K⁺ and N, endogenous H₂S and L-DES activity, but reduced H₂O₂ and MDA contents, membrane leakage and leaf B. Silicon-induced B tolerance was further enhanced by 0.2 mM NaHS, a H₂S donor. A scavenger of H₂S, hypotaurine (0.1 mM HT), was supplied together with Si and Si + NaHS to assess the involvement of H₂S in Si-induced BT tolerance of pepper plants. Hypotaurine inverted the positive role of Si on the antioxidant defence system by reducing endogenous H₂S, but NaHS supply along with Si + HT reversed the negative effects of HT, showing that H₂S participated in Si-induced BT tolerance of pepper plants.

Keywords: Antioxidant defence system; Boron toxicity; Hydrogen sulphide; Oxidative stress; Pepper; Silicon.