Mitigation of salinity stress in cucumber seedlings by exogenous hydrogen sulfide

This research hypothesized that tolerance of cucumber seedlings to salinity stress could be increased by hydrogen sulfide (H₂S) treatments. In pot experiments, the cucumber seedlings were exposed to three levels of salt stress (0, 50 and 100 mM NaCl), and NaHS as H₂S donor was foliar applied to the cucumber seedlings at five different doses (0, 25, 50, 75 and 100 µM). The effects of the treatments on cucumber seedlings were tested with plant growth properties as well as physiological and biochemical analyses. As the salinity level increased, plant growth properties and chlorophyll reading value (SPAD) decreased. However, H₂S treatments significantly mitigated the impact of salinity. Salt stress elevated the membrane permeability (MP) and decreased the leaf relative water content (LRWC). H₂S applied leaves had lower MP and higher LRWC than non-H₂S applied leaves. On the other hand, photosynthetic properties (net photosynthetic rate, stomatal conductance, transpiration rate and intercellular CO₂ concentration) of the seedlings under salt stress conditions were decreased but this decrease was considerably relieved by H₂S treatment. The K/Na and Ca/Na ratios under salt stress conditions were higher in H₂S-applied plants than in non-applied plants. Furthermore, antioxidant enzyme activity [(catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD)] and hydrogen peroxide (H₂O₂), malondialdehyde (MDA), proline, and sucrose concentration in the leaves increased with salinity stress whereas they were reduced with H₂S treatments under salt stress. Mitigation of salt stress damage in cucumber using H₂S treatment can be expounded via modulation of enzyme activity, nutrient content, reactive oxygen species (ROS) formation, and osmolytes accumulation.