Melatonin alleviates cadmium toxicity in Solanum nigrum by enhancing pectin-mediated cell wall sequestration and antioxidant.

Abstract

Cadmium (Cd) contamination in agricultural soils threatens crop production and food safety. Although melatonin is known to enhance antioxidant defense, its role in cell-wall remodeling and Cd compartmentalization remains unclear. We investigated the effects of 100 μmol L-1 melatonin on Solanum nigrum exposed to 10 mg kg-1 Cd using physiological, biochemical, subcellular, transcriptional, and random forest analyses. Cd reduced biomass, photosynthetic rate, and Fv/Fm, whereas melatonin partially restored these traits. Melatonin also decreased Cd concentrations in roots, stems, and leaves and reduced root-to-shoot Cd translocation. Meanwhile, Cd partitioning to the cell-wall fraction increased from 56.7% to 67.5% in roots and from 55.1% to 66.5% in leaves, while organellar Cd partitioning was approximately halved. These changes were accompanied by increased pectin content and pectin-bound Cd, upregulation of pectin metabolism and Cd detoxification genes, enhanced antioxidant activity, and improved redox status. Random forest modeling identified ascorbate, photosynthetic rate, and pectin-bound Cd as key predictors of Cd tolerance. These findings indicate that melatonin enhances Cd tolerance through coordinated cell-wall sequestration and antioxidant defense while altering Cd allocation, with implications for phytoremediation efficiency.