Different effects of pretreatment with tritiated thymidine (<sup>3</sup>H-dTh) on radiation-induced sister chromatid exchanges (SCEs) and micronuclei inVicia faba root tip cells

Abstract

Primary roots ofVicia faba were grown for 24 h in the presence of tritiated thymidine (1.85-18.5 kBq ml-1) and then irradiated with a dose of 1.5 Gy of60Co-gamma- rays. The aim of these experiments was to determine whether low-level endogenous beta-irradiation from incorporated radioactive thymidine could influence the frequencies of sister chromatid exchanges (SCEs) and the numbers of micronuclei induced by subsequent external irradiation with high doses of gamma-rays. The results demonstrated that the pretreatment with3H-dTh had no significant effect on the frequencies of SCEs in gamma-irradiated root tip cells ofVicia faba. In contrast to SCEs, the yields of micronuclei in the3H-dTh pretreated cells were altogether less than the yield induced by gamma-rays alone (protective effects).