Hydrogen Sulfide-Mediated Physiological, Biochemical, and Ultrastructural Modifications Enhance Drought Tolerance in Common Bean (Phaseolus vulgaris L.)

The common bean (Phaseolus vulgaris L.cv. BR-104) is the most widely cultivated legume crop and serves as a major dietary protein source worldwide. However, climate change-induced drought poses a severe threat to its productivity by disrupting key physiological and biochemical processes. Therefore, identifying effective strategies to enhance drought resilience in the common bean is of considerable importance. The present study investigates the regulatory role of hydrogen sulfide (H2S) in improving drought tolerance. Polyethylene glycol (15% PEG) induced drought stress markedly reduced phenotypic changes (leaf area (LA), plant dry weight (PDW), root length (RL), and shoot length (SL) by 18.6, 20.5, 30.3 and 17.5% respectively), photosynthetic efficiency (Fv/Fm by 28.4%), and photosynthetic pigment concentrations (chlorophyll and carotenoids by 25.6 and 36%, respectively), while significantly elevating oxidative stress markers (H2O2 and TBARS by 137.1% and 169.8%, respectively), leading to impaired stomatal movement and damaged chloroplast structure. Exogenous H2S application as sodium hydrogen sulfide (200 µM NaHS; H2S donor) effectively alleviated drought-induced oxidative damage by boosting endogenous H2S and GSH levels, upregulating activity of antioxidative enzymes, SOD, APX, and GR, thereby promoting reactive oxygen species (ROS) scavenging, and minimizing lipid peroxidation. Moreover, H2S maintained photosynthetic efficiency via improved stomatal openings and chloroplast structure, thus sustaining chlorophyll levels and stabilizing photosystem-II functionality. Enhanced proline accumulation following NaHS application led to improved osmotic adjustment, thereby contributing to overall stress tolerance. The use of a H2S scavenger at 100 µM HT (Hypotaurine) suppressed the mitigating effects of H2S, confirming the role of H2S in enhancing drought tolerance in the common bean. Collectively, these findings highlight the potential effect of H2S as a regulatory signaling molecule to enhance drought resilience in the common bean under drought stress conditions. Further research should explore integrating H2S-based treatments with breeding programs and agronomic practices to develop sustainable strategies to improve drought resilience in legumes and other staple crops under changing climatic conditions.