Foliar Fe2O3 nanoparticles enhance cadmium tolerance in Amaranthus hypochondriacus by modulating cell wall immobilization and antioxidant defenses

The integration of nanotechnology with high biomass plants offers a sustainable strategy for rehabilitating cadmium (Cd)-contaminated lands. However, the potential of iron-based nanoparticles (Fe-NPs) to enhance Cd phytoremediation in the hyperaccumulator Amaranthus hypochondriacus remains unclear. The current study demonstrates that foliar spraying of 100 mg L −1 Fe-NPs (α-Fe 2 O 3 ) alleviated Cd (10 mg kg −1 )-induced growth inhibition (plant height, leaf area, and biomass), and partially restored leaf photosynthetic parameters and chloroplast morphology. Fe-NPs also reduced Cd-triggered oxidative damage by decreasing reactive oxygen species (ROS) and malondialdehyde (MDA) levels while enhancing antioxidant activities in leaves. Moreover, Fe-NPs treatment significantly increased Cd accumulation in leaves and total Cd extraction, indicating enhanced phytoremediation efficiency. Meanwhile, Fe-NPs modified the subcellular Cd distribution in leaves, increasing cell wall Cd fixation from 56.8 % to 61.57 %. Transcriptomic analysis revealed that Fe-NPs + Cd treatment induced the most differentially expressed genes (1097 upregulated, 572 downregulated), mainly enriched in DNA-binding, protein catalysis, chloroplast function, cell wall dynamics, metal ion binding. Notably, Fe-NPs upregulated a group of wall-associated receptor-like kinase ( WAKL ) genes that were downregulated by Cd. Furthermore, AhWAKL16 overexpression in hairy roots significantly increased cell wall Cd content by 14 % and mitigated Cd-induced root elongation inhibition and MDA accumulation. This work highlights the potential of Fe-NPs for Cd remediation in A. hypochondriacus, and provides the first evidence that Fe-NPs enhance Cd tolerance, at least partially, through WAKL -mediated Cd immobilization in the cell wall. • Iron oxide nanoparticles (Fe-NPs) improve Cd phytoremediation in A. hypochondriacus. • Fe-NPs enhance Cd tolerance by maintaining leaf redox homeostasis and photosynthesis. • Fe-NPs increase Cd fixation in the cell wall of leaf contributing to Cd tolerance. • Fe-NPs remodel the expression of genes involved in cell wall and ion transport. • AhWAKL16 positively regulates Cd tolerance via immobilizing Cd in the cell wall.