Foliar nano-molybdenum application mitigates cadmium-induced apoplastic H₂O₂ burst in rice roots by optimizing the antioxidant system

Cadmium (Cd²⁺) exhibits pronounced phytotoxicity and poses significant risks to human health through bioaccumulation in agricultural products. This study investigates the mitigative effects of foliar-applied nano-molybdenum particles (MoNPs) on Cd accumulation and growth rates in rice (Oryza sativa). Our findings demonstrate that MoNPs application effectively alleviates Cd-induced root growth suppression and reduces Cd deposition in root cell walls, through MoNPs-mediated attenuation of Cd-induced elevation of pectin content. Through cross-sectional analysis combined with ROS-specific fluorescent probes revealed a spatial pattern of Cd-induced H₂O₂ accumulation, with strongest signals observed in the apoplastic regions of root elongation and maturation zones, with minimal accumulation in meristematic regions. This oxidative burst was significantly mitigated by MoNPs treatment, which enhanced plasma membrane (PM)-localized respiratory burst oxidase homolog (RBOH) activity via transcriptional upregulation of OsRBOH genes. Furthermore, foliar MoNPs application activated the ascorbate–glutathione (ASA-GSH) cycle through selective upregulation of OsAPXs and OsGRs, enhancing cellular capacity for H₂O₂ detoxification. These coordinated mechanisms collectively suggest that MoNPs treatment offers dual protection against Cd toxicity by 1) reducing Cd bioavailability in plant tissues and 2) counteracting Cd-induced oxidative damage, thereby effectively ameliorating root growth inhibition under Cd stress.