Exogenously supplied silicon (Si) improves cadmium tolerance in pepper (Capsicum annuum L.) by up-regulating the synthesis of nitric oxide and hydrogen sulfide.

• Cadmium (Cd) stress reduced plant growth, generates oxidative stress and activates antioxidant defense system. • Application of Silicon (Si) enhanced plant growth and mitigates the oxidative stress induced by Cd. • Si supplementation enhanced endogenous nitric oxide (NO) and hydrogen sulphide (H 2 S) that helps in Cd stress tolerance. • cPTIO (NO scavenger) and hypotuarine, HT (H 2 S scavenger) decreased the NO and H 2 S level and antioxidant defense system • Both NO and H 2 S played a great role in Si-induced Cd tolerance in pepper plants. The current research was aimed to observe the interactive role of silicon-generated hydrogen sulfide (H 2 S) and nitric oxide (NO) on tolerance of pepper (Capsicum annum L.) plants to cadmium (Cd). Thus, the pepper plants were subjected to control (no Cd) or cadmium stress with and without Si supplementation. Significant decreases were found in plant dry weights, water potential, PSII maximum efficiency, glutathione (GSH), total chlorophyll, relative water content, Ca2+ and K+ concentrations and ascorbate, but there was a significant increase in H 2 O 2 , MDA, electron leakage (EL), proline, key antioxidant enzymes' activities, and endogenous Cd, NO and H 2 S in the Cd-stressed plants. Silicon enhanced Cd tolerance of the pepper plants by lowering the leaf Cd concentration, oxidative stress, enhancing the antioxidant defence system, leaf Si content, photosynthetic traits and plant growth as well as the contents of NO, proline and H 2 S. Furthermore, foliar-applied NO scavenger, cPTIO, and that of H 2 S, hypotaurine (HT), significantly decreased the levels of H 2 S alone, but cPTIO effectively reduced the concentrations of NO and H 2 S accumulated by Si in the Cd-stressed plants. The positive effect of Si was eliminated by cPTIO, but not by HT, suggesting that both molecules were involved in Si-induced improvement in Cd tolerance of the pepper plants. [ABSTRACT FROM AUTHOR]