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

Abstract

Cadmium (Cd) toxicity is a major environmental stressor that adversely affects plant growth, photosynthesis, and metabolic processes, leading to oxidative damage and reduced crop productivity. This study investigates the role of nitric oxide (NO) and hydrogen sulphide (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 hydrosulphide), individually and in combination, significantly alleviated Cd toxicity. The combined NO + H₂S treatment showed the highest shoot and root length increase (~60% over Cd-stressed plants), improved chlorophyll and carotenoid content (~87% restoration to control levels), and reduced oxidative damage, as indicated by lower malondialdehyde (MDA) (~40%) and hydrogen peroxide (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. These findings indicate that NO and H₂S act as key stress modulators by reducing oxidative damage, enhancing antioxidant defenses, and improving physiological resilience under Cd stress. The synergistic effects of NO + H₂S provide new insights into gasotransmitter-mediated stress mitigation strategies, offering potential applications for developing Cd-tolerant crop varieties and improving sustainable agricultural practices in metal-contaminated environments.