From plant barriers to stress resilience: a framework for evaluating productive nano-delivery in plants

Abstract

Nano-enabled agriculture has the potential to improve the efficiency and precision of agricultural inputs, yet the field lacks a rigorous framework for distinguishing nanoparticle accumulation from productive functional delivery. This review develops a nano-to-phenotype framework that categorizes plant nano-systems into three functional classes: intrinsically bioactive nanoparticles, carrier-based delivery systems, and hybrid systems. A nine-level evidence framework is proposed, progressing from surface association and tissue accumulation to cellular internalization, subcellular localization, cargo integrity, cargo release, target engagement, molecular response, and phenotype. Each level defines the evidence required to support a mechanistic claim and distinguishes it from evidence demonstrating nanoparticle presence alone. Application of the framework to plant barrier interactions, uptake, intracellular trafficking, and stress responses reveals that many claims of nano-enabled delivery rely primarily on evidence of nanoparticle accumulation rather than functional cargo delivery. Detection of intact particles within tissues or cells does not establish cargo release or target engagement, while phenotypic responses may be incorrectly attributed to cargo without excluding particle-intrinsic effects. A causal attribution framework is therefore proposed using comparisons among free cargo, unloaded carrier, loaded carrier, and appropriate dissolved-ion or molecular controls. Evidence strength is evaluated across reproducibility, mechanistic resolution, dose–response characterization, environmental realism, and agronomic relevance. Sustainability is considered through functional efficiency, input displacement, environmental fate, non-target effects, and life-cycle burden rather than material origin alone. The framework identifies intracellular trafficking and target engagement as major mechanistic gaps, while field validation and integrated sustainability assessment remain important translational challenges. The central question is therefore not whether nanoparticles enter plants, but whether evidence establishes a causal chain from nanoparticle exposure to functional delivery and agronomically meaningful outcomes.