Phytotoxicity and Genotoxicity Evaluations of Chromium Hexavalent (CrVI) on Allium cepa and Nigella sativa Root Cells

Abstract

AS ONE of the leading global causes of environmental contamination, heavy metals hurt agriculture and human health through the food chain. Using the mitotic index (MI), chromosomal aberrations (CAs), and DNA damage, the cytotoxic and genotoxic effects of Cr(VI) on the root tips of Allium cepa and Nigella sativa were assessed. Six Cr(VI) concentrations (50, 100, 400, 700, 1000, and 2000ppm) were administered for 6, 12, 18, and 24h. The germination percentages of A. cepa and N. sativa seeds decreased at 400ppm for both plants, without germination detected in N. sativa L. at or above 700 ppm. The MI in the treated group was significantly lower than the control cells after exposure to the various concentrations of Cr(VI) for different exposure times. The reduction of MI in N. sativa root tips was more pronounced than that of A. cepa. The largest abnormal percentages were identified in N. sativa after 24h of exposure to 100ppm Cr(VI), whereas A. cepa showed abnormal percentages after 24h of exposure to 400ppm Cr(VI). In all mitotic phases, distinct aberrations in the division of root tip cells were observed in both plant species. A few examples of these aberrations were stickiness, C-mitosis, anaphase–telophase bridges, disturbed laggards, and micronuclei. The comet test, which show the single-strand breaks in DNA, was used to determine how dangerous is Cr(VI) to DNA in A. cepa root cells. DNA damage was significantly obvious in the comet experiment than in the control at all concentrations. Evidence from both A. cepa and N. sativa root meristemic cells suggested that Cr(VI) is cytotoxic and genotoxic and induces DNA damage in a dose-dependent manner.