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

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.