Hydrogen Peroxide Is Involved in Methane-Alleviated Cadmium Toxicity in Alfalfa ( L.) Seedlings by Enhancing Cadmium Chelation onto Root Cell Walls.

Although previous studies have demonstrated that methane (CH) can mitigate the toxicity of cadmium (Cd) in alfalfa seedlings, the CH-rich water used in these studies may create hypoxic conditions, potentially influencing the experimental outcomes. Therefore, this study aimed to investigate whether CH can reduce Cd toxicity in alfalfa seedlings without the interference of hypoxia and to analyze its underlying mechanisms. Here, it was observed that supplementing oxygen with saturated CH-rich water can significantly alleviate the inhibition of 75 μM CdCl on the growth of alfalfa ( L.) seedlings. Less Cd accumulation was also observed in both root and shoot parts, which could be explained by the CH-altered cell wall components in alfalfa seedling roots, including covalent and ionic soluble pectin, and the degree of demethylation in pectin, thus enabling a higher proportion of Cd binding to the cell walls and reducing the entry of Cd into the cells. The above actions of CH were accompanied by an increase in hydrogen peroxide (HO) content and NADPH oxidase activity, which could be blocked by the addition of the NADPH oxidase inhibitor diphenylene iodonium (DPI). Taken together, these results implied that exogenously applied CH could alleviate Cd toxicity in alfalfa seedlings by enhancing Cd chelation onto the root cell walls, which might be closely associated with NADPH oxidase-dependent HO signals. These findings could provide insight into the mechanism through which CH alleviates Cd toxicity in alfalfa plants.