Salicylic acid-induced hydrogen sulphide improves lead stress tolerance in pepper plants by upraising the ascorbate-glutathione cycle.

The contribution of hydrogen sulphide (H2 S) to salicylic acid (SA) induced lead (Pb) stress tolerance modulated by the ascorbate-glutathione (AsA-GSH) cycle was examined in pepper (Capsicum annuum L.) plants. One week after germination, pepper seedlings were sprayed with 0.5 mM SA once a day for a week. Thereafter, seedlings were grown under control (no Pb) or Pb stress (Pb-S treatment consisting of 0.1 mM PbCl2 ) for a further 2 weeks. Lead stress reduced plant growth and leaf water status as well as the activities of dehydroascorbate reductase and monodehydroascorbate reductase. However, lead stress elevated leaf Pb, the proline contents, oxidative stress, activities of glutathione reductase and ascorbate peroxidase, as well as the endogenous H2 S content. Supplements of SA resulted in improvements in growth parameters, biomass, leaf water status and AsA-GSH cycle-related enzyme activities, as well as increasing the H2 S content. The positive effect of SA was further enhanced when sodium hydrosulphide was added. However, 0.1 mM hypotaurine (HT) treatment reversed the beneficial effect of SA by reducing the plant H2 S content. Application of NaHS in combination with SA + HT suppressed the adverse effect of HT mainly by restoring the plant H2 S content, suggesting that higher H2 S content, induced by exogenous SA supply, resulted in elevated regulation of the AsA-GSH cycle.