Iron Deficiency Reduces Cadmium Translocation in Peanut by Increasing the Root Cell Wall Reservoir

Iron (Fe) deficiency and cadmium (Cd) contamination often co-occur in agricultural systems, yet the way in which Fe deficiency modulates Cd translocation remains unclear. Here, we investigated root cell wall modifications mediating Cd accumulation in two peanut cultivars with contrasting Fe deficiency tolerance. Fe deficiency significantly increased root Cd concentrations in both cultivars but reduced Cd translocation to shoots, an effect more pronounced in the tolerant cultivar Silihong. Cell wall analysis revealed cultivar-specific compositional changes: pectin and cellulose increased under combined Cd exposure and Fe deficiency, while hemicellulose (HC1) decreased. Negative correlations between Fe and Cd accumulation in roots, cell walls, and their components indicate competition between these two metal ions for binding sites in root cell walls. Increased pectin content under combined stress enhances Cd sequestration, while reduced HC1 content facilitates Fe mobilization to shoots. Transcriptomic analysis identified hub genes associated with cell wall modification, including pectinesterases (PME2/4/29/63), beta-galactosidases (BGAL3/5/8), polygalacturonases (PGs), pectin acetylesterases (PAE8), xyloglucan endotransglucosylase/hydrolases (XTH8/31) and laccases (LAC7/11/15). Under combined stress, Silihong exhibited superior Cd immobilization, characterized by higher Cd accumulation in HC1 and cellulose fractions, stronger induction of PME, PAE8 and LAC genes, and greater suppression of XTHs, PGs, and BGALs. Our findings demonstrate that Fe deficiency restricts Cd translocation by remodeling root cell walls, increasing pectin and cellulose while modulating hemicellulose integrity, thereby creating an expanded apoplastic reservoir that traps Cd. This structural detoxification mechanism, operating downstream of uptake transporters, identifies key cell wall components and regulatory genes as potential targets for breeding peanut cultivars with improved food safety.