Effects of Zinc Oxide Nanoparticles on Growth and Secondary Metabolite Accumulation in In Vitro Culture of Ocimum basilicum L.

Abstract

The study investigated the effects of zinc oxide nanoparticle (ZnO-NP) on the growth, secondary metabolite accumulation, and antioxidant activity of Ocimum basilicum L. (basil) shoots in vitro. Various concentrations of ZnO-NP (5, 10, 20, 40 and 50 mg/L) were applied to assess their impact on growth parameters such as shoot elongation, node and leaf numbers, shoot multiplication rate, root formation percentage, and root length. Results showed that lower ZnO-NP concentrations stimulated shoot elongation, while higher concentrations negatively affected root development. Total phenolic content (TPC) and antioxidant activity were assessed in methanolic extracts, with higher TPC observed in roots compared to stems. The antioxidant capacity, evaluated using DPPH and CUPRAC assays, showed variable responses to ZnO-NP concentrations, with higher antioxidant activity (SC50: 0.77 mg/mL and 0.512 mmol TE/g plant, respectively) detected at 40 mg/L ZnO-NP concentration in roots. Additionally, the study analyzed rosmarinic acid content, the main phenolic compound in O. basilicum, and found that its accumulation increased with ZnO-NP application, especially in roots at the 40 mg/L ZnO-NP concentration with the value of 35.98 µg phenolic/mg plant. Overall, the findings suggest that ZnO-NP application influences growth, secondary metabolite accumulation, and antioxidant activity in O. basilicum, with effects varying based on concentration and plant part.