Apoplast-Confined Nanozyme Catalysis for Selective 1O2 Generation and Host Defense in Plants

Abstract Reactive oxygen species (ROS)-based antimicrobial strategies in plants are often constrained by limited oxidant selectivity and collateral phytotoxicity. Here, we report an apoplast-confined nanozyme that integrates selective singlet oxygen (1O2) catalysis with host defense activation. The copper–iron Prussian blue analogue nanozyme CuFePBA exhibits oxidase-like activity under physiologically relevant conditions, converting molecular oxygen into 1O2 without detectable generation of superoxide or hydroxyl radicals. Following foliar application, CuFePBA is retained within the apoplast because of exclusion from the symplast by the plant cell wall. In this extracellular compartment, localized 1O2 production damages bacterial membranes, suppresses respiration, and eliminates apoplastic pathogens while minimizing intracellular oxidative stress. The resulting apoplastic redox perturbation also elicits a transient intracellular ROS burst, promotes cell wall reinforcement, activates pattern-triggered immunity, and induces sustained expression of defense-related genes. Through this catalytic-immunological coupling, CuFePBA enhances disease resistance in planta without detectable phytotoxicity. These findings establish spatially confined nanozyme catalysis as an effective strategy for combining antimicrobial activity with host-compatible immune activation and highlight microenvironmental confinement as a general design principle for biologically compatible nanomaterials in plant protection.