Abstract
Hydrogen sulfide (H2S) has emerged as a potential regulator of plant responses to abiotic stress. In this study, we investigated the effects of exogenous sodium hydrosulfide (NaHS) on tobacco seedlings subjected to polyethylene glycol (PEG)-induced drought stress. Compared to control conditions, drought stress significantly reduced several parameters in tobacco seedlings, including shoot dry weight (22.83%), net photosynthesis (37.55%), stomatal conductance (33.56%), maximum quantum yield of PSII (Fv/Fm) (11.31%), photochemical quantum yield of PSII (ΦPSⅡ) (25.51%), and photochemical quenching (qP) (18.17%). However, applying NaHS, an H2S donor, mitigated these effects, ultimately enhancing photosynthetic performance in tobacco seedlings. Furthermore, optimal NaHS concentration (0.4 mmol/L) effectively increased leaf relative water content (RWC) and root activity while promoting the accumulation of soluble sugars and proline content to maintain osmotic pressure balance under drought stress. NaHS pretreatment also bolstered the antioxidant defense system in leaves, leading to a reduction in hydrogen peroxide (H2O2) and malondialdehyde (MDA) content and an increase in the activities of antioxidant enzymes such as ascorbate peroxidase (APX), superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Consequently, NaHS protected chloroplast structure and attenuated chlorophyll degradation, thus mitigating severe oxidative damage. Overall, our findings provide valuable insights into exogenous NaHS's role in enhancing tobacco drought tolerance. These results lay the foundation for further research utilizing H2S-based treatments to improve crop resilience to water deficit conditions.