Amelioration of Cadmium-Induced Stress in Tomato (Solanum lycopersicum) Using Gasotransmitters: A Combined Approach to Enhancing Antioxidant Defense and Growth Resilience

Cadmium (Cd) toxicity is a major environmental stressor that adversely affects plant growth, photosynthesis, and metabolism, causing oxidative damage and yield loss. This study investigates the role of nitric oxide (NO) and hydrogen sulfide (H₂S) in mitigating Cd-induced stress in Solanum lycopersicum by analyzing growth parameters, oxidative stress markers, antioxidant enzyme activity, and physiological responses. Tomato seedlings exposed to Cd (20 µM CdCl₂) exhibited severe growth inhibition, leaf chlorosis, chlorophyll degradation, and increased oxidative stress. Exogenous application of NO (sodium nitroprusside) and H₂S (sodium hydrosulfide), individually and in combination, significantly alleviated Cd toxicity. The combined NO + H₂S treatment showed the highest increase in shoot and root length (~60% over Cd-stressed plants), improved chlorophyll and carotenoid content (87% restoration to control levels), and reduced oxidative damage, indicated by lower malondialdehyde (MDA) (40%) and H₂O₂ (55%) accumulation. Antioxidant enzyme activities (SOD, CAT, APX, POD) were significantly upregulated, enhancing reactive oxygen species (ROS) detoxification. Additionally, proline accumulation (~4-fold increase) and protein content (~30% restoration) were improved, suggesting better osmotic balance and metabolic stability. NO and H₂S mitigate Cd stress by reducing oxidative damage, boosting antioxidant defenses, and enhancing resilience. Their combined action highlights gasotransmitter-based strategies for developing Cd-tolerant crops and promoting sustainable agriculture in metal-contaminated soils.