Cell wall binding mechanism provides insights into preferential cadmium accumulation in senescent leaves of tall...

Cadmium (Cd) contamination poses a serious threat to food security and human health. Phytoremediation technology remains constrained by challenges in the mechanism of plant Cd uptake and accumulation. Cd preferentially accumulates in senescent leaves of tall fescue (Festuca arundinacea), offering a phytoremediation strategy through harvesting of senescent leaves. However, the underlying mechanism driving Cd accumulation in senescent leaves remains poorly understood. Here, we elucidate the cell wall-associated Cd-binding mechanism during leaf senescence using an integrated approach combining physiological, transcriptomic, metabolomic, and proteomic analyses. Physiological studies revealed that Cd binding to the cell wall played a central role in Cd accumulation during leaf senescence. Pectin, particularly in the forms of water-soluble pectin and chelating-soluble pectin, was identified as the primary site for Cd binding. A significant decrease in pectin methylesterification was observed during leaf senescence. Fourier-transform infrared spectroscopy (FTIR) further indicated that cell wall functional groups, especially hydroxyl (-OH) and carboxyl (-COOH) groups, are involved in Cd binding. Transcriptomic, metabolomic, and proteomic analyses revealed substantial upregulation of pectinesterases during senescence, which contributed to decreased pectin methylesterification and exposure of free carboxyl groups, facilitating Cd binding. Our findings demonstrated that decreased pectin methylesterification and exposure of -OH and -COOH groups in the cell wall constituted the key mechanisms underlying Cd preferential accumulation in senescent leaves. This insight offers a promising pathway to enhance phytoremediation efficiency and facilitate innovation through targeted harvesting of senescent leaves.