Influence of 1-p-D-arabinofuranosylcytosine on mitotic activity of apical meristem of onion (Allium cepa L.) roots

The influence of increasing cytosine arabinoside (ara-C) concentration (50, 100, 300 and 500 μg/ml) on the mitotic activity of the apical meristem of onion adventitious roots was investigated during 24-h incubation in ara-C and postincubation in water. Incubation in ara-C inhibits reversibly mitosis, the degree of inhibition being dependent on the concentration used. 50 μg/ml ara-C causes only a slight and transitional mitotic depression, while 100—500 μg/ml reduces the per cent of mitoses in various degrees after 12-h incubation whereas after 24 h all concentrations (100—500) reduce mitosis to the same level of about 2 per cent (80% inhibition). During postincubation in water there occurs after treatment with 100—500 μg/ml ara-C, a wave of highly synchronized mitoses with a peak after 12 h. The highest frequency of synchronized mitoses (60°/o) appeared in roots treated with 300 μg/ml ara-C. The main wave is preceded by a small one with a peak after 2-4 h of postincubation. This seems to be the consequence of phases S and G₂ inhibition by ara-C. It was found that under the influence of ara-C the per cent of mitoses with chromosome aberration and of cells with micronuclei increased only slightly.