Selenium and zinc oxide nanoparticles stimulate product quality, phenolic content, antioxidant activity, and shikonin production in Italian bugloss (Echium italicum L) plantlets under in vitro conditions

Italian bugloss, scientifically known as Echium italicum L., is an important medicinal plant that produces valuable secondary metabolites, including shikonin. The present study investigates the effects of zinc oxide nanoparticles (ZnO NPs) and selenium nanoparticles (Se NPs) on the phytochemical composition and morphophysiological traits of E. italicum under in vitro conditions. Accordingly varing concentrations of ZnO NPs (0, 25, 50, and 75 mg/L) and ZnO NPs (0, 5, 10, and 20 mg/L) were applied. The findings revealed that the application of ZnO NPs and Se NPs generally promoted biomass accumulation and morphological growth parameters, as well as enhanced antioxidant activity (DPPH radical scavenging and ferric reducing antioxidant power, FRAP), total phenolic content (TPC), total flavonoid content (TFC), phenylalanine ammonia-lyase (PAL) activity, glutathione peroxidase (GPX) and ascorbate peroxidase (APX) activities, and shikonin production. Furthermore, ZnO NPs (75 mg/L) remarkably increased chlorophyll content (a, b) and carotenoid by 153.52%, 61.15%, and 391%, respectively, compared to the controls. The highest shikonin content (410 µg/g DW) was achieved at 75 mg/L ZnO NPs, representing an 81.89% increase compared to the control plants. Treatment with Se NPs at a concentration of 10 mg/L exerted the most pronounced effects on physiological and phytochemical traits compared to other treatments, as evidenced by the data cluster heatmap. The findings of this study demonstrated that Se NPs and ZnO NPs promise effective approaches for enhancing shikonin and phenolic antioxidants under in vitro conditions.