From stress to defense: Spatial confinement of nanoplastics in rice root cell walls via pectin matrix remodeling

Nanoplastics (NPs), ubiquitous environmental pollutants, are increasingly documented to accumulate in plants and induce phytotoxicity. However, the mechanisms governing their cellular-level interactions with plants, particularly root cell wall adaptations to limit translocation, remain unresolved. Here, we elucidate how rice (Oryza sativa L.) root cell walls employ pectin-mediated remodeling to immobilize europium-doped polystyrene NPs (PS-Eu NPs) under hydroponic conditions. Exposure to 50 mg/L PS-Eu NPs for 14 days resulted in 96.94 % retention in roots and only 3.06 % translocation to shoots. Remarkably, root pectin content surged by 64.7 %, directly enhancing NP entrapment (43.9 % of total PS-Eu NPs bound to pectin). This pectin-driven response induced structural reorganization of the cell wall, characterized by increased thickness, stiffness, and adhesiveness, which collectively immobilized 51.47 % of NPs within root cell walls and suppressed upward transport. Multi-omics analyses further uncovered coordinated upregulation of pectin biosynthesis genes (e.g., galacturonosyltransferases, 26-80 %) and modification enzymes (e.g., pectin methylesterases, 12-63 %), accompanied by elevated polysaccharide metabolic intermediates. These findings establish that pectin-dominated cell wall fortification is a critical plant defense strategy to mitigate NP stress, providing mechanistic insights into cellular barriers against nanoparticle translocation in agroecosystems.