Deoxyribonucleic acid synthesis and the production of chromosomal aberrations by streptonigrin, 8-ethoxycaffeine and 1,3,7,9-tetramethyluric acid

Abstract

Autoradiographic experiments, in which Vicia faba roots were treated with [ 3H]thymidine in combination with streptonigrin (SN), 1,3,7,9-tetramethyluric acid (TMU) or 8-ethoxycaffeine (EOC), were performed in order to investigate the sensitivity of the various phases of the cell cycle to the production of chromosomal aberrations. It appeared in these studies that SN, TMU and EOC were all able to induce chromatid aberrations during the post-DNA-synthesis or G 2 phase. During the period of DNA synthesis (the S phase), chromatid aberrations were produced by SN and EOC. Streptonigrin appeared to be at least as effective during S as during G 2. The effect produced by EOC during the S phase was considerably weaker than that produced in G 2 cells and consisted mainly of isolocus breaks localized in the nucleolar constriction (Fig. 2a). The results further indicate that SN and EOC are able to induce chromosome type aberrations in the G 1 phase, i.e., the interphase period between telophase and S. TMU did not produce any aberrations in S and G 1 cells. In experiments with excised Vicia roots, approx. 50% inhibition of the incorporation of 32P-labelled phosphate into DNA was obtained with 1.5·10 −5 M SN and with 1.5·10 −2 M TMU, the period of treatment being 3 h in both cases. The incorporation of 32P-labelled phosphate into RNA was also affected but to a lesser extent, the figures obtained being 27 and 37% for SN and TMU, respectively. In a previous study 12, EOC was found to be even more effective as an inhibitor of DNA and RNA synthesis. The results and the mechanisms of action of SN, TMU and EOC are discussed. It is concluded that the chromosomal aberrations and the inhibition of nucleic acid synthesis are two independent affects of changes produced by the substances in chromosomal DNA.