In vivo genotoxicity assessment of nickel oxide nanoparticles in the model plant Allium cepa L

Plants are continuously exposed to high concentrations of engineered nickel oxide nanoparticles (NiO-NP) from increasingly contaminated soil and water. As they are the primary producers in any ecosystem, their behaviour to NiO-NP excess merit closer scrutiny. Ni is an essential micronutrient. Existing reports confirm phytotoxicity of NiO-NP, primarily through ROS paroxysm induced when they enter and accumulate in plant tissues. In the present study, the authors have endeavoured to deduce the link between chromosomal aberrations occurrence and cell cycle perturbations in Allium cepa in response to NiO-NP. A wide range of NiO-NP concentrations (10-500 mg L-1) were taken to understand dosage effect on cell cycle discrepancies. Detailed assessments of cytotoxic and genotoxic markers, like changes in the frequency of MI, MN and aberration indices, showed that with increase in NiO-NP concentration induced genotoxicity were noted. Instances of clastogenic and physiological aberrations, coincided with a dose dependent decrease in MI. This was concomitant with a dip in G1 population and sharp increase at the G2/M peak as seen using Flow Cytometry in samples undergoing similar treatment regimes. Maximum perturbation in the cell cycle dynamics coincided with maximum MI loss and increased frequency of aberrations. Instances of extreme low MI, heavy chromosomal condensation and disarray at the highest concentrations of NiO-NP used (250-500 mg L-1) were also reported. This led to initiation of cell death cascades, as evident from minimizing of the G1 population. Therefore, these finding suggest that NiO-NP affected nuclear and chromosomal integrity and disrupted the cell cycle progression in plants.