Silicon alleviates cadmium toxicity in muskmelon (Cucumis melo): integrative insights from photosynthesis to antioxidant activity to gene expression

Abstract

Cadmium (Cd) toxicity is a potential abiotic stress that significantly affects plant growth and development, especially in vegetable crops like muskmelon. Silicon (Si), a vital element, plays an essential role in alleviating Cd-induced stress by various mechanisms. The present study explored the impact of Cd and Si treatments at 25, 50, 100, and 200 mg per kg soil concentrations on the physio-biochemical and molecular changes in muskmelon. Si treatment stabilized key physiological factors like increasing photosynthesis by 16% to 98%, decreasing electrolyte leakage by 28% to 69%, and increasing the relative water content by 7% to 48%, respectively, under increasing concentrations of Cd treatments supplemented with Si, improving the overall plant health. The results indicated that Cd exposure led to increased oxidative damage, as evidenced by the levels of hydrogen peroxide, malondialdehyde, and proline, under a maximum concentration of 200 mg kg⁻¹ with respective fold increases of 3.44, 2.84 and 5.03, while Si supplementation significantly mitigated these effects, with respective fold changes of 0.83, 0.92 and 0.87, under similar concentrations, when compared with the control plants. Si enhanced the activity of the antioxidant enzyme and improved the gene expression associated with oxidative stress, providing a protective effect against Cd-induced damage. Si also promoted nutrient uptake and alleviated the unfavourable impacts of Cd on soil physio-biochemical properties, like pH, electrical conductivity (EC), and organic carbon (OC) content. The combined application of Cd and Si showed a synergistic effect, enhancing plant resilience and reducing Cd accumulation. These findings suggest that Si is an effective strategy for mitigating Cd toxicity, improving plant health, and promoting crop productivity, particularly in muskmelon and other vegetable crops.