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 (HS) 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, HS, and activities of catalase, superoxide dismutase, peroxidase, and L-DES. Silicon stimulated growth, proline content and activities of various antioxidant biomolecules and enzymes, leaf Ca, K and N, endogenous HS and L-DES activity, but reduced HO and MDA contents, membrane leakage and leaf B. Silicon-induced B tolerance was further enhanced by 0.2 mM NaHS, a HS donor. A scavenger of HS, hypotaurine (0.1 mM HT), was supplied together with Si and Si + NaHS to assess the involvement of HS in Si-induced BT tolerance of pepper plants. Hypotaurine inverted the positive role of Si on the antioxidant defence system by reducing endogenous HS, but NaHS supply along with Si + HT reversed the negative effects of HT, showing that HS participated in Si-induced BT tolerance of pepper plants.