Studies on the effects of phleomycin on chromosome structure and nucleic acid synthesis in Vicia Faba

Abstract

Chromosomal aberrations were produced in Vicia faba root-tips by 1-h treatments with pheleomycin at concentrations of 0.03 and 0.1 mg/l. The aberrations obtained were of sub-chromatid, chromatid and chromosome type. When, in autoradiographic experiments, bean roots were fixed 5 h after being exposed for 1 h to a mixture of tritiated thymidine and phleomycin, all the sub-chromatid and the majority of the chromatid aberrations obtained occurred in unlabelled cells, which suggests that they were produced after the completion of DNA synthesis. When roots were fixed 22 h after treatment, most of the chromatid aberrations occurred in labelled cells. This finding shows that not only cells that have completed DNA synthesis, but also cells in the stage of DNA synthesis, are sensitive to the chromosome-breaking effect of phleomycin. Furthermore, the occurrence of chromosome-type aberrations in cells fixed 20–30 h after treatment suggests that phleomycin is also able to produce aberrations in the presynthesis stage G 1. The effect of phleomycin on the incorporation of 32P into DNA and RNA was studied in experiments with excised root-tips of Vicia faba. The concentration of phleomycin required to produce a significant inhibition of the incorporation of 32P into DNA in excised Vicia roots was about 300 times higher than the concentration required to produce chromosomal aberrations in intact lateral roots of Vicia. The incorporation of 32P into RNA was inhibited by phleomycin to almost the same extent as the incorporation into DNA. Phleomycin proved to be considerably more active as a chromosome-breaking agent in the absence than in the presence of oxygen. When the phleomycin solution was stored for 2 h before the treatment, the aberration yield was less than 15% of that produced by a freshly-prepared solution, irrespective of the gas phase during storage. This suggests that the higher effect obtained with phleomycin under anaerobic conditions was not a result of a slower inactivation of the aqueous phleomycin solution in the absence of oxygen.