2000 Volume 65 Issue 3 Pages 277-287
The present investigation was carried out to study the cytological effects of the herbicide atrazine on Allium cepa and Vicia faba with respect to the cell cycle response, mitotic index, chromosome aberrations and nucleic acids content. The root of young seedlings of V. faba and adventitious roots of A. cepa were treated with the following concentrations : 25%, 50%, 75% and 100% of the recommended dose (3.75 g/l) for 4, 8, 12, 24 h. The results indicated that atrazine herbicide reduced the mitotic division in both plants compared to the respective control. Mitotic index values were progressively decreased with increased the concentration and treatment time. In V. faba, the treatment with the concentration of 100% for each treatment time (4, 8, 12, 24 h) was toxic, but in A. cepa, the same concentration with 24 h was only toxic. The percentage of the reduction in MI values in V. faba was higher than that in A. cepa. Also, it has been clearly observed that the inhibition of mitotic division was associated with reduction in DNA and RNA contents in both treated plants root tips. This may point out that the inhibition of mitotic activity is due to a deficiency of DNA in the nucleus. The increased percentage of prophase in both plants was accompanied by decreased percentages of the other mitotic phase. The total percentage of aberrations increased with the increasing the concentration of atrazine herbicide and the period of treatment. The total percentage of aberrations in A. cepa was higher than that in V. faba for each treatment. Different abnormal mitotic figures were observed in all mitotic phases. Such types of abnormalities were stickiness, lagging, C-mitosis, bridges, irregular prophase, unequal distribution, fragments and a few cells with micronucleus at interphase stage.