African Journal of Food, Agriculture, Nutrition and Development, Vol 9, No 5
OA Asita, R Makhalemele, National University of Lesotho
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Over the past decade, issues of animal use and care in toxicology research and testing have become one of the fundamental concerns for both science and ethics. Emphasis has been given to the use of alternatives to mammals in testing, research and education. Because plants are direct recipients of agrotoxics and therefore important material for genetic tests and for environmental monitoring of places affected by such pollutants, three doses each of the pesticides, dithane (0.196, 0.391, 0.782 % solution), malathion (0.034, 0.069, 0.137 % solution) and garden ripcord (1.015, 2.030, 4.060 % solution) were assessed for cytotoxicity and genotoxicity to onion root tip cells.
The doses represented the LC50 (dose that inhibited 50 % of seeds from germinating), ½ LC50 and ¼ LC50 for each pesticide that were determined in a preliminary dose selection experiment. Onion seeds were germinated on moistened filter paper in a petri dish at room temperature until radicles appeared. Germinated seeds were exposed to three concentrations of each pesticide for 20 hours.
About 1- 2mm length of root tip was cut, fixed in acetic alcohol, washed in ice cold water, hydrolyzed in warm 1N hydrochloric acid, stained with aceto-carmine and squashed on glass microscope slide. About 3000 cells were scored for each treatment and classified into interphase and normal or aberrant division stage. Cytotoxicity was determined by calculating the mitotic indices and comparing the mitotic indices of treated cells at each dose of each pesticide with that of the negative control group.
The mitotic index of the negative control group was reduced to half or less, at the two highest doses of all three pesticides. All three pesticides were therefore cytotoxic to the onion root tip cells. Genotoxicity was measured by comparing the number of cells/1000 in the aberrant division stages at each dose of each pesticide with the number of such cells in the negative control group using the Mann-Whitney statistical test. Dithane was genotoxic (P< 0.05), inducing multipolar anaphases and telophases and lagging chromosomes. Malathion was genotoxic (P< 0.05), inducing lagging chromosomes. Garden ripcord was not genotoxic.