The Production of Chromatid Aberrations by5-FluorodeoxyuridineAlone and in Combination with X-Rays and8-Ethoxycaffeine

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Abstract
Cell-divisions containing chromosomal aberrations began to appear in lateral root-tips of Vicia faba about 3 hours after immersion of the roots in solutions containing FUDR in concentrations of 0.5 μor higher. The aberrations consisted mainly of gaps and chromatid breaks. Aberrations involving rejoining (isochromatid breaks with sister-union, exchanges) were extremely rare. Concentrations of FUDR which produced chromosome breakage also had a strong inhibitory effect on mitosis. Between 6 and 24 hours after the beginning of the treatment, very few cell-divisions occured. Fifteen to thirty per cent of the cells dividing 24–26 hours after a. 1-hour treatment with 1 μ FUDR contained chromatid aberrations, which now were of the « usual » type, i.e., isochromatid breaks with sister-union and chromatid exchanges. The effect of modifying factors was studied and it was found that the effect of FUDR increased with temperature and was stronger at low than at high pH. Anaerobic conditions during the treatment and pre-treatments with 2.4-dinitrophenol considerably reduced the radiomimetic effect of FUDR. Post-treatments with thymidine or 5-bromodeoxyuridine suppressed the effect of FUDR. When X-irradiation was combined with a FUDR-treatment, which by itself produced very few aberrations, there was a strong increase in the number of gaps, chromatid breaks and metaphases with extreme fragmentation in comparison with the X-ray control. When EOC was combined with FUDR, the effect was smaller than the sum of the effect of EOC and FUDR alone. FUDR did not affect the frequencies of EOC-induced exchanges and isochromatid breaks with sister-union. Thé effcct of FUDR, on the other hand, was markedly reduced by EOC.