Dual role of hydrogen sulfide in modulating photosynthesis, antioxidant defense, and membrane integrity in Cucurbita pepo

Although traditionally regarded as a toxic environmental gas, hydrogen sulfide (H2S) has recently been recognized as a gasotransmitter involved in regulating various physiological processes in both plants and animals. This study aimed to investigate the stage- and concentration-dependent effects of exogenous H2S on the growth, photosynthetic capacity, and antioxidant performance of squash (Cucurbita pepo) plants. Fifteen-day-old seedlings were subjected to foliar application of H2S at different concentrations (0, 25, 50, 75, 100, 200, and 300 μM) and monitored until the end of the experiment. Plant samples were collected at two distinct intervals following H2S treatment – 24 hours and 15 days to comprehensively assess growth, physiological, and biochemical parameters. The results revealed a biphasic response to H2S treatments. Application of 100 μM H2S significantly improved growth traits (including shoot and root length, dry biomass, and leaf area), photosynthetic performance, carbonic anhydrase activity, antioxidant enzyme activities, and proline accumulation, while reducing electrolyte leakage and lipid peroxidation compared to untreated controls. In contrast, higher concentrations (200 and 300 μM) adversely affected these parameters and caused increased cellular damage. These findings suggest that 100 μM H2S is the optimal concentration for enhancing physiological and biochemical traits in squash and may serve as a promising tool for improving crop productivity via improved photosynthetic and stress-response mechanisms.