INDUCTION OF CHROMOSOME MUTATIONS IN CREP IS-CAPILLARIS CELLS BY METHYL METHANESULFONATE AND 4-NITROQUINOLINE-N-OXIDE AND MODIFICATION OF MUTAGENESIS BY DNA-SYNTHESIS INHIBITORS

Mutagenic effect of S-dependent mutagens - methyl methanesulfonate (MM S) and 4-nitroquinoline-N-oxide (4-NQO) has been studied in the first mitosis of germinating Crepis capillaris seeds in early, middle and la te G1-phase, S- and G2)-phases of cell cycle. It is shown that MMS in the studied concentrations has no mutagenic effect while acting in all the studied phases. The frequency of mutations is within the range of control. Hydroxyurea (HU), the DNA synthesis 1840 inhibitor, introduc ed in the phase of DNA post-synthesis, 3h before each fixation, does n ot modify MMS effect in all the studied cases. Mutagenic effect of 4-N QO has been shown only with high concentration (5.10(-5) M, up to 6%). The spectrum of rearrangementes, induced in early G1-phase, is repres ented mainly by chromatid type aberrations. Monoadducts, induced by 4- NQO in early G1-phase, survive up to S-phase and result in chromatid a berrations in G2-phase. The rate of induced aberrations from damages, inflicted by 4-NQO in this phase under the action of HU 5.10(-3) M or caffeine 5 mM, is not high - it is close to authehticity or is negligi ble. In case of combined action of HU and caffeine mutation frequency decreases. Higher sensitivity of 4-NQO is shown in late G1 + S phase t han in early G1 phase. HU, caffeine and combined action of the 2 inhib itors modifies mutagenic effect of 4-NQO in this phase through its sen sibilization. Damages induced in late G1 phase are not modified in to chromosome type aberrations in G2.