Tungsten Oxide Nanoparticles Trigger a Light-Independent Stress Response and Metabolic Reprogramming from Phenylpropanoids to Benzoates in Ocimum basilicum Suspension Cultures

• Tungsten oxide nanoparticles (WO 3 NPs) trigger a dose-dependent, light-independent stress response in basil cultures. • Low doses induce a hormetic effect, enhancing biomass and antioxidant capacity. • Metabolic profiling reveals a putative carbon re-routing from growth-related phenylpropanoids to defense-related benzoates. • A proposed mechanistic model links tungsten-induced stress to metabolic priming and defense-related survival strategy. • WO 3 NPs may act as "dark-elicitors modulating plant resilience without light activation. Engineered tungsten trioxide nanoparticles (WO₃ NPs) are often described as potent stressors for plants within the context of visible-light photocatalysts, but their effects in complete darkness remain poorly understood. This study investigated the dose-dependent effect of WO₃ NPs (0, 50, 50, 100, 200 and 300 mg L⁻¹) on Ocimum basilicum (basil) cell suspension culture in complete darkness over a comprehensive time-course (6, 8, 12, 24 and 48 h). The results revealed a distinct hormetic stress paradigm. Low-dose exposure (50–100 mg L⁻¹) acted as a metabolic priming signal, significantly increasing biomass (up to 20%) and stimulating the biosynthesis of high-value antioxidants, such as vanillin and catechin, alongside enhancing non-enzymatic antioxidant defenses (total phenolics and flavonoids) and ascorbate peroxidase (APX) activity. Conversely, higher concentrations (200–300 mg L⁻¹) induced a selective metabolic reprogramming, characterized by a systemic shift from growth-related phenylpropanoids (such as rosmarinic and ferulic acids) towards defense-oriented benzoate derivatives (including gallic and vanillic acids) in addition to increasing the activity of superoxide dismutase (SOD) and catalase (CAT). This metabolic redirection suggests a putative inhibition of the nitrate reductase (NR) pathway, nitric oxide (NO)-salicylic acid (SA) signaling axis and triggering a growth-defense trade-off. These findings decipher the potential of WO₃ NPs as light-independent triggers, establishing their role as dark-elicitors capable of modulating plant resilience and secondary metabolism without the need for light activation. This offers a new mechanistic framework for precision nano-elicitation in sustainable agriculture and plant biofactories.