Mitochondrial and Chromosomal Damage Induced by Oxidative Stress in Zn2+ Ions, ZnO-Bulk and ZnO-NPs treated Allium cepa roots

Bilal Ahmed,Abdulaziz A Al-Khedhairy,Sourabh Dwivedi,Malik Zainul Abdin,Ameer Azam,Javed Musarrat,Quaiser Saquib,Mohammad Saghir Khan,Majed Al-Shaeri

doi:10.1038/srep40685

Abstract

Large-scale synthesis and release of nanomaterials in environment is a growing concern for human health and ecosystem. Therefore, we have investigated the cytotoxic and genotoxic potential of zinc oxide nanoparticles (ZnO-NPs), zinc oxide bulk (ZnO-Bulk), and zinc ions (Zn2+) in treated roots of Allium cepa, under hydroponic conditions. ZnO-NPs were characterized by UV-visible, XRD, FT-IR spectroscopy and TEM analyses. Bulbs of A. cepa exposed to ZnO-NPs (25.5 nm) for 12 h exhibited significant decrease (23 ± 8.7%) in % mitotic index and increase in chromosomal aberrations (18 ± 7.6%), in a dose-dependent manner. Transmission electron microcopy and FT-IR data suggested surface attachment, internalization and biomolecular intervention of ZnO-NPs in root cells, respectively. The levels of TBARS and antioxidant enzymes were found to be significantly greater in treated root cells vis-à-vis untreated control. Furthermore, dose-dependent increase in ROS production and alterations in ΔΨm were observed in treated roots. FT-IR analysis of root tissues demonstrated symmetric and asymmetric P=O stretching of >PO2− at 1240 cm−1 and stretching of C-O ribose at 1060 cm−1, suggestive of nuclear damage. Overall, the results elucidated A. cepa, as a good model for assessment of cytotoxicity and oxidative DNA damage with ZnO-NPs and Zn2+ in plants.

Highlights

In this study, we have characterized the zinc oxide nanoparticles (ZnO-NPs) using UV-Vis spectroscopy, X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) analyses, and demonstrated the (i) internalization of ZnO-NPs in A. cepa root tissues by FTIR, TEM and SEM, (ii) intracellular reactive oxygen species (ROS) production, mitochondrial and chromosomal damage induced by bulk ZnO, Zn2+, and ZnO-NPs in A. cepa root cells using DCFH-DA, and Rh-123 fluorescence probes, and TEM imaging, and (iii) proposed a plausible mechanism of ZnO-NPs interaction and cellular damage in plant tissue
Nanoparticles were characterized by UV-Visible, fluorescence, FT-IR spectroscopy, X-ray diffraction, TEM and SEM-EDX analyses (Fig. 1 Panels A–F)
A sharp fluorescence emission peak of ZnO-NPs was obtained at 385 nm (Fig. 1A solid line), which corresponds to the near band gap excitonic emission

Summary

Introduction

To the best of our understanding no systematic study either in qualitative or quantitative terms on ZnO-NPs induced plant root tissue damage, intracellular localization, intracellular ROS generation, mitochondrial damage, and chromosomal aberrations has been reported. With this aim, we have chosen A. cepa, as a model, for comparative assessment of the cytotoxic and genotoxic effects of ZnO-NPs, bulk ZnO and Zn2+ ions. In this study, we have characterized the ZnO-NPs using UV-Vis spectroscopy, XRD, FTIR, TEM and SEM analyses, and demonstrated the (i) internalization of ZnO-NPs in A. cepa root tissues by FTIR, TEM and SEM, (ii) intracellular ROS production, mitochondrial and chromosomal damage induced by bulk ZnO, Zn2+, and ZnO-NPs in A. cepa root cells using DCFH-DA, and Rh-123 fluorescence probes, and TEM imaging, and (iii) proposed a plausible mechanism of ZnO-NPs interaction and cellular damage in plant tissue

Methods

Results

Discussion

Conclusion