Mitigating stress and boosting metabolites through the impact of ZnO nanoparticles on <i>Stevia rebaudiana</i> and <i>Ocimum basilicum</i>

Plant growth is usually compromised by abiotic and biotic stressors that decrease germination, yield, and synthesis of useful metabolites. Zinc oxide nanoparticles (ZnO-NPs) have exhibited potential in increasing plant tolerance and metabolic yield. This research assesses the impact of ZnO-NPs on <i>Stevia rebaudiana</i> and <i>Ocimum basilicum</i> in a randomized pot experiment with seed priming at concentrations of 0-250 mg L^-1. The nanoparticles were identified through UV-vis spectroscopy (maximum absorption at 380 nm), FTIR, and XRD, proving their crystalline hexagonal wurtzite nature and functional groups (C = O, C-O, O-H). Germination in <i>O. basilicum</i> was highest at 50 mg L^-1, with maximum shoot and root growth at 100 mg L^-1, whereas Stevia showed a positive response only at 50 mg L^-1. GC-MS analysis revealed remarkable enhancement of fatty acids, phenols, and terpenes in ZnO-NP treatment. These observations imply ZnO-NPs have the potential to promote plant growth and secondary metabolite production, yet species- and dose-dependent effects need to be considered with care.