Abstract:The clastogenic (chromosome-damaging) effect of many chemical and physical agents is believed to be mediated by reactive oxygen-detived radicals. The interaction of these free radicals with DNA and the significance of the radical-induced DNA lesions in mutagenesis and carcinogenesis have been the subjects of increasing interest during recent years. Sister chromatid exchange (SCE) reflects an interchange between DNA molecules at homologous loci within a replicating chromosome. SCE analysis was found to have increased use for monitoring the exposure of cell to mutagenic carcinogens. The authors found that the induction of SCEs in cells of Hordeum vulgare L. by ascorbic acid, mitomycin C, adriamycin and maleic hydrazid was through the action of free radicals. They also studied the influence of growth temperature on average generation time(AGT) and SCEs. and disclosed a close correlation between AGT and SCEs. The Brdu-Giemsa techniques were used for the detection of SCEs and AGT in cytological preparations of metaphase chromosomes.