Nanoparticles (NPs) can stimulate biosynthesis of bioactive compounds in plants. Mn NP is a less explored NP, and very little is known about interactions between Mn2O3 NPs and plants. The present study was conducted to explore the potential effects of Mn2O3 NPs on morphology, physiology and secondary metabolism of shoot tip cultures in the medicinal plant deadly nightshade (Atropa belladonna). The MS culture medium was augmented with different concentrations (25, 50, 100 and 200 mg L−1) of Mn2O3 NPs, and the medium with or without manganese sulfate (MnSO4·4H2O) was considered as positive and negative control, respectively. The addition of Mn2O3 NPs to culture media led to changes in morphology (root and shoot number per explants, root and shoot length, and root and shoot fresh weight) and physiology (leaf relative water content, total chlorophyll, hydrogen peroxide and malondialdehyde contents, electrolyte leakage and membrane stability index) by altering the protein content and activation of antioxidant and defense enzymes (superoxide dismutase, peroxidase, catalase and ascorbate peroxidase) and regulation of pharmacologically active metabolites (total phenolics, flavonoids and alkaloids) biosynthesis in a dose-dependent manner. All the extracts obtained from plantlets grown in various culture media showed DPPH% free radical scavenging and Fe2+- chelating activities to different degrees. The index of integrated biological marker response (IBR/n) for different antioxidant enzymes was differentially influenced by various concentrations of Mn2O3 NPs. An UPGMA dendrogram of cluster analysis was also constructed, which divided all the studied treatments into three major groups (toxic, positive and inconsequential). At appropriate dosage (25 mg L−1), Mn2O3 NPs were found to be stimulant of both plant growth and metabolic processes such as production of alkaloids. Thus, Mn2O3 NPs would be a novel extracellular elicitor of secondary metabolites for tissue culture systems i
