Effect of Hydrogen Sulfide on Physiological and Biochemical Parameters in Two Barley Varieties Under Drought Stress

Abiotic stresses reduce barley growth and yield by elevating the free radicals such as reactive oxygen (ROS), nitrogen (RNS), carbonyl (RCS), and sulfur species (RSS) in plant cells. Among these, hydrogen sulfide (H2S), classified as RSS, serves as a signalling molecule and growth regulator in stress responses. However, the optimal sodium hydrosulphide (NaHS; an H2S donor) concentrations for barley (Hordeum vulgare L.) remain unknown. In this study, two barley cultivars (Kalaycı-97 and Yaprak) were treated with exogenous NaHS at different concentrations (0.1, 0.3 and 0.5 mM) and then exposed to drought stress. The results showed that NaHS applications increased chlorophyll content, reduced root length, and altered plant growth responses in a dose- and genotype dependent manner under drought conditions. Furthermore, it increased endogenous H2S levels in both varieties under drought conditions, leading to a decrease in H2O2 levels, an indicator of oxidative stress. In conclusion, it was shown that NaHS, particularly at concentrations of 0.3 mM and 0.5 mM, helped reduce the detrimental effects of oxidative stress in both varieties, and that genotypic differences played a significant role in this regulation. These findings highlight that NaHS regulates drought tolerance in a genotype-specific manner, strengthening enzymatic antioxidant defenses in the susceptible Kalaycı-97 while activating non enzymatic mechanisms in the tolerant Yaprak.