INTERPHASE SENSITIVITY TO CHROMOSOME-BREAKING EFFECT OF 2'-DEOXYADENOSINE - AN AUTORADIOGRAPHIC STUDY

Root tips of Vicia faba were treated with 7.5-8[center dot]10-3 M 2[image]-deoxyadenosine (AdR) and exposed to 2 [mu]C/ml tritiated thymidine before, after or simultaneously with the AdR treatments. Various times after the treatments, root tips were fixed and slides prepared as Feulgen squashes. Stripping film autoradiographs were then made and after a 14-day exposure the slides were developed and analyzed for aberration yield and the presence of silver grains over-laying the chromosomes. The results obtained suggest that there are 2 types of interphase cells which are sensitive to the chromosome-breaking effect of AdR: cells which are preparing for DNA synthesis and chromosome duplication (cells in late G1 or very early S) and cells which have completed chromosome duplication and are preparing to divide (cells in G2). The aberrations induced in late G1 or early S were mainly chromatid exchanges and isolocus breaks, but a few chromosome-type exchanges were also found. The majority of the chromatid interchanges produced in these cells were localized in the nucleolar constriction. Most of the cells affected by AdR in G2 proceeded without much delay towards mitosis. The aberrations found in these cells were of the fragment type, i.e., they consisted mostly of gaps and chromatid breaks. However, the data suggest that a fraction of the cells affected while in G2 were considerably delayed and did not reach mitosis until about the same time as the cells which were affected by AdR while in late G1. These cells contained aberrations of the exchange type.