Engineered nanoparticles at the redox interface: Rewiring ROS signaling and stress responses in plants

Engineered nanoparticles (ENPs) are increasingly recognized as promising tools for modulating plant stress responses; however, their underlying mechanisms and associated risks remain under debate. This review integrates recent advances showing that ENPs can reprogram plant redox homeostasis through multiple pathways, including direct surface redox activity, nanozyme-like catalysis, ion release, and disruption of organellar electron transport. In addition, ENPs influence membrane physicochemical properties, transcriptional regulation, metabolic fluxes, hormonal crosstalk, epigenetic modifications, and the structure of the plant-associated microbiome. These processes produce distinct reactive oxygen and nitrogen species (ROS/RNS) signatures that activate Ca²⁺ fluxes, mitogen-activated protein kinase (MAPK) cascades, and downstream transcriptional networks. We emphasize the importance of dose-dependent-often hormetic-responses, the critical role of the rhizosphere microbiome, and the application of spatially resolved techniques (e.g., μ-XRF, NanoSIMS, and spatial omics) to link NP fate with localized redox dynamics. Finally, we propose a safe-by-design framework that incorporates standardized NP characterization, appropriate ionic and inert controls, and predictive modeling approaches. This framework aims to facilitate the risk-informed and sustainable deployment of ENPs in agriculture.