MUTAGENICITY OF BLEOMYCIN AND CROSS-ADAPT ATION WITH ALKYLATING-AGENTS IN CREPIS-CAPILLARIS

The radiomimetic effect of bleomycin (BLM) at concentrations of 5 and 10 mg/l on root meristem cells was studied. The roots of germinating s eeds of Crepis capillaris were exposed to BLM 16 h after the seeds wer e soaked. At this time, the root meristem cells were at the S or late G(1) phase of the cell cycle. The mutagenic effect of BLM was found wh en the cells were fixed at the 29th, 32nd, 36th, 39th, 42nd, or 45th h our (i.e., the early germinating fraction). The aberrations induced in cluded chromosome and chromatid rearrangements. At late fixations, cel ls were observed, which had, in addition to definite double-hit aberra tions, multiple chromosomal breaks and pronounced chromosomal fragment ation. A hypothesis is advanced that BLM causes inducibIe repair that is similar to SOS-repair. This repair is prone to DNA synthesis errors , which account for the increase in the number of aberrations at late fixation times. Pretreatment with 1 mu g/ml of mitomycin C, an alkylat ing agent, before the exposure to 10 mg/l BLM, resulted in cross-adapt ation, which drastically reduced the number of BLM-induced aberrations . This was especially evident for the number of aberrations and the nu mber of cells affected at late fixations.