Elicitation of Secondary Metabolites in Callus Cultures of Stevia rebaudiana Bertoni Grown Under ZnO and CuO Nanoparticles Stress

Abstract

Accumulation of secondary metabolites in medicinal plants by giving abiotic/biotic stress is, nowadays, an active area of research. This study reports the inoculation of ZnO and CuO nanoparticles in Murashige and Skoog (MS) medium having plant growth regulators for the regeneration of callus from leaf explants of medicinal plant, Stevia rebaudiana. Presence of ZnO and CuO nanoparticles in different concentrations results in conferring different kinds of physiology in different regenerants. 1 and 10 mg/L have been declared the best ZnO and CuO nanoparticles concentrations regarding various physiological parameters. Steviol glycosides have not been detected in any callus treatment. Moreover, the phytochemical characteristics of S. rebaudiana under different ZnO and CuO nanoparticles concentrations have been exploited. The highest amount of total phenolic content (TPC), total flavonoid content (TFC), total antioxidant capacity (TAC) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity has been obtained at 100 mg/L of ZnO nanoparticles, whereas TPC, TAC, TRP and DPPH free radical scavenging activity have been achieved highest at 10 mg/L concentration of CuO nanoparticles. However, the highest TRP in the context of ZnO and the highest TFC regarding CuO have been achieved at 50 and 100 mg/L, respectively. This clearly indicates that CuO nanoparticles are more toxic to Stevia callus as compared to ZnO nanoparticles, and opens avenues for future studies utilizing ZnO or CuO nanoparticles for the enhancement of commercially important secondary metabolites in different medicinal plants.