Ionic Stress Induced Cytotoxic Effect of Cadmium and Nickel Ions on Roots of Allium cepa L.

The cytotoxic effects of low doses (20 to 100 mu M) of nickel ions (Ni) and cadmium ions (Cd) as well as antioxidative enzyme changes in Allium cepa roots were studied. Heavy metal induced oxidative damage showed significant reduction in root length, mitotic index, total protein content and catalase (CAT) activity and increased cell abnormality index as well as proline content. Enhanced antioxidative enzyme activities were noticed to minimize oxidative stress by increasing guaiacol peroxidase (GPX) activity of the tissue. The effect of toxicity was found to be dose dependent in antioxidative enzyme level and more pronounced in root systems. Evans blue uptake by the root cells showed the cell death parameter which served as an indicator of cytotoxicity. Recovery experiments till 48h showed significant changes in antioxidative enzyme systems of the cells reverting back to normal. Treatment of Ni and Cd led to spindle abnormalities like multipolarity, sticky bridge in anaphase, early separation, clumping of chromosomes, late separation as well as direct chromosomal damage with chromosome break, chromosome erosion, laggard chromosomes. This experiment explains the role of reactive oxygen in heavy metal toxicity and their DNA damage, cell death and adaptive responses to genotoxic challenges of the cells amelioration.