Glutathione-induced hydrogen sulfide enhances drought tolerance in sweet pepper (Capsicum annuum L.)

Glutathione (GSH) has been studied for its potential to enhance stress tolerance in plant systems, but the role of hydrogen sulfide (H₂S) in GSH-induced water stress tolerance in sweet pepper (Capsicum annuum L.) is still under investigation. This study explores how H₂S and GSH modulate water stress tolerance in pepper plants, addressing a research gap. The joint effect of sodium hydrosulfide (NaHS), a donor of H₂S, and GSH on water stress tolerance was determined through pre-treatment with the H₂S scavenger 0.1 mM hypotaurine (HT). Pepper seedlings were sprayed with 1.0 mM GSH or GSH + 0.2 mM NaHS once a week, with soil moisture content set at 80% and 40% for full irrigation and water stress conditions for a duration of 2 weeks. The results showed that water stress significantly reduced total plant dry weight, chlorophyll a and b content, Fv/Fm, leaf water potential, and relative water content by 50%, 56%, 33%, 27%, 52%, and 34%, while increasing hydrogen peroxide (H₂O₂), proline, and H₂S levels by 152%, 134%, and77%, respectively. Treatment with GSH and NaHS reduced water stress-induced H₂O₂ production and improved plant growth, photosynthetic traits, proline, and the activity of L-cysteine desulfhydrase (L-DES), leading to the generation of H₂S content. GSH reduced NADPH oxidase (NOX), superoxide dismutase (SOD), and H₂O₂ but increased glutathione peroxidase (GPX) activities. The interaction of NaHS and GSH led to further reductions in NOX, SOD, and H₂O₂ values but increased GPX activity. The combined GSH and NaHS treatment increased nitric oxide (NO) production but decreased the activity of S-nitrosoglutathione reductase (GSNOR), potentially accelerating S-nitrosylation. Hypotaurine negated the positive impacts of GSH on water stress tolerance by reducing H₂S concentration in pepper plants, but this was corrected by the concurrent application of NaHS and GSH + HT. Therefore, water stress tolerance requires H₂S.