Nano-elicitors improve plant stress resistance by regulating secondary metabolisms: mechanisms and application strategies

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Plant secondary metabolites are important natural sources in the fields of medicine, food and cosmetics, and also play an important defensive role in plants' adaptation to environmental stresses such as drought, saline-alkali and pathogen infection. Traditional elicitors can boost metabolite buildup and stress resistance, but their lack of specificity, inconsistent effectiveness, and limited dosage ranges might exacerbate the trade-offs between growth and defense. Nano-elicitors offer tunable physicochemical properties and controlled-delivery capabilities, yet the relationships between material design, plant context, signalling and metabolic outcomes remain fragmented. This paper review synthesizes detailed synthesis of current evidence regarding the role of nanotechnology in regulating plant secondary metabolism and stress responses. Based on their composition, nanomaterials are classified into five categories: metallic NPs, metal-oxide NPs, non-metallic NPs, carbon-based NPs and nanocomposites. Across these categories, a structure–activity framework links size, morphology, surface charge, functionalization, dissolution and dosage to plant uptake, taxon-dependent responses, hormesis and toxicity. After crossing plant barriers, or interacting with the cell wall–plasma membrane interface, nanomaterials can activate interacting Ca²⁺, reactive oxygen species, mitogen-activated protein kinase and phytohormone signalling modules. Their outputs can converge on transcription-factor networks and metabolic enzymes, redirecting carbon, nitrogen and energy towards flavonoid, alkaloid and terpenoid biosynthesis. Meanwhile, studies consistently demonstrate that appropriately dosed nano-elicitors can alter secondary-metabolite abundance and stress-related phenotypes. In response to challenges such as an incomplete understanding of the underlying mechanisms, limited long-term environmental safety evidence, and remaining constraints on large-scale application, future directions such as intelligent responsive nano-elicitors, deep coupling of nanomaterials and synthetic biology, and machine learning-assisted material design and mechanism analysis are discussed. The cross-integration of the above-mentioned directions is expected to promote the development of nanomaterials from experimental tools into controllable engineering platforms, providing scientific support for enhancing crop stress tolerance and the sustainable production of high-value plant natural products.