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

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-a-vis untreated control. Furthermore, dose-dependent increase in ROS production and alterations in Delta Psi m 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.