In vitro effect of zinc oxide nanoparticles on Nicotiana tabacum callus compared to ZnO micro particles and zinc sulfate (ZnSO4)

Abstract

Nano-technology has changed the properties of metal elements’ delivery into and effect on living systems. The current study, first, evaluated different combinations of plant growth regulators NAA, 2,4-d and KIN on Nicotiana tabacum callus induction from root, internode, petiole and leaf explants. Two mg L−1 NAA with 0.1 mg L−1 KIN on Murashige and Skoog (MS) medium induced calli in all explant sources. Then, the effect of different concentrations of nP-ZnO (0.015, 0.03, 0.06, 0.12, 0.24 mM) and µP-ZnO (0.03, 0.06, 0.12, 0.24 mM) compared to ZnSO4 (0.03 mM) on cell toxicity was investigated. SEM microscopy, XRD and EDX analyses were used to determine particles characteristics. Higher zinc content was accumulated in calli under nP-ZnO concentrations compared with µP-ZnO, which was positively correlated with calli fresh and dry weights. The nP-ZnO induced oxidative stress more significantly than µP-ZnO. Protein content did not increase under µP-ZnO, while it was raised at all concentrations of nP-ZnO that had positive correlation with MDA and ROS. SOD enzyme activity increased at all levels of µP-ZnO but remained unchanged under all levels of nP-ZnO compared to control. Ferric reducing antioxidant power (FRAP) was more sensitive than α, α-diphenyl-β-picrylhydrazyl (DPPH) for determining plant antioxidant capacity under nP-ZnO stress. The result showed that nP-ZnO induced a combined growth promoting and stress-induction effect in tobacco callus cells in a dose-dependent manner. The toxicity level of nP-ZnO was ameliorated compared to similar µP-ZnO concentrations. The chemical bio-reactivity of nP-ZnO-based Zn2+ could cause its fast-responsive and modified influence in tobacco cells. ZnO nanoparticles increased Zn2+ bioavailability in tobacco callus but ameliorated metal toxicity. Zinc nanoparticles induced dose-dependent and combined oxidative and growth promoting effects. FRAP was recommended for nP-ZnO oxidative studies.