Biogenic synthesis of metal oxide nanoparticles for the elicitation of secondary metabolites in the in vitro propagated plantlets of Rubia cordifolia L.

In recent decades, nanoparticles (NPs) have become an important focus of research with diverse applications in industries such as food, cosmetics, and medicine. Recent studies have demonstrated that nanomaterials can boost the production of secondary metabolites in plants. In vitro techniques coupled with nanotechnology tools provide an attractive alternative for enhancing the production of targeted dye products (Alizarin and Purpurin) from crops. In this study, biocompatible hexagonal-shaped Zinc oxide nanoparticles and monoclinic-spherical-shaped Copper oxide nanoparticles (CuO NPs) were synthesized from the stem extract of Rubia cordifolia L., with average particle sizes of 17.9 nm and 28.35 nm, respectively. Quantitative phytochemical assessments, HRLC-MS analysis, HPTLC fingerprinting, and antioxidant properties in methanolic extracts of in vitro treated plants with different concentrations of metallic oxide NPs showed variations, in both quality and quantity of secondary metabolites. The treatment of 0.1 mg/L CuO NPs showed the highest level of secondary metabolites including alizarin and purpurin. Notably, concentrations exceeding 10 mg/L transformed these nanoparticles from elicitors to potentially toxic components for the plantlets. The extracts elicited by CuO NPs (0.1 mg/L) exhibited high antioxidant activity due to these metabolic changes. CuO NP treatment provided a useful and efficient in vitro technique to enhance the synthesis of plant based bioactive compounds with potential applications in the pharmaceutical and textile industry.