Melatonin enhances the cadmium tolerance of mushrooms through antioxidant-related metabolites and enzymes.

Many wild mushroom species are known to immune heavy metals. However, the mechanism by which this occurs remains largely unsolved. Melatonin (MT) has been proven to play an important defensive role against various abiotic stresses in plants and animals. This study reports on the presence of MT in edible fungi and its role in the response to cadmium (Cd)-induced stress. We found that melatonin was widely distributed in all experimental species and could also relieve Cd-induced damage in the Volvariella volvacea. Comparative metabolic and proteome analyses reveal that tryptophan/proline/tyrosine metabolism, the citrate cycle, nitrogen and glutathione metabolism, and oxidation-reduction processes were enriched after Cd and/or MT addition, indicating an antioxidant mechanism was aroused. Finally, different MT and cadmium treatments were studied for their effects on the expression and activity of oxidation-related enzymes (superoxide dismutase, catalase, peroxidase, etc), which further verified the ameliorative influence of MT on Cd-induced oxidative stress.