Modifying of radiation damage to chromosome by 5-fluorine-2-deoxyuridine and thymidine at different stages of the mitotic cycle

The effect of X-radiation (300 R) on cells of Crepis capillaris L. sprouts (phases G1, S and G2) was modified by 5-fluorine-2-deoxyuridine (FUdR), thymidine and a mixture of FUdR and thymidine. under the effect of FUdR, and unusual spectrum of chromosome aberrations was observed which showed an increase in simple chromatid breaks and in isochromatid breaks, without rejoining, and also a drastic deficiency of exchange. A decreased level of modified cells was registered under the effect of thymidine. The ''protective'' effect of thymidine was most pronounced at G2 and S phases. Thymidine decrease number of intrachromosomal and interchromosomal exchnge aberrations. A combination of FUdR and thymidine does not markedly influence the cytogenetic effect of radiation and has no effect on number of X-radiation-induced aberrations of different types