Comparative study of the sensitivities of onion and broad bean root tip meristematic cells to genotoxins

Chemicals which cause chromosomal aberration (CA) in plant cells frequently produce identical CA in cultured animal cells. Plant species however, differ in sensitivities. Onion and broad bean (BB) rootmeristem cells were compared for sensitivity to chlorpyrifos (CPF), mercury chloride (HgCl2), ethyl methanesulphonate (EMS) and garden ripcord (GR). Seeds were germinated on moist filter paper until radicles appeared and exposed to three doses of each chemical for 24 h. About 1 - 2 cm length of root tip was cut, fixed, washed and hydrolyzed in 1 N HCl. Root tips were transferred to microscope slides, cut 2 mm from the growing tip, stained, covered with cover slip and squashed. Cytotoxicity was inferred when the mitotic index (MI) of treated cells was £ ½ of control. All chemicals were toxic to onion cells but only EMS and HgCl2 were toxic to BB. Genotoxicity was determined by analyzing 100 anaphase and telophase cells for chromosome fragments, bridges, vagrant chromosome, c-anaphase, multipolarity and stick chromosomes and aberrations at each dose compared with the control using the chi-squared test. All chemicals were genotoxic (P < 0.05) to onion but only CPF, HgCl2 and EMS were genotoxic to BB. Onion was more sensitive to 10 of 13 genotoxicity indices used