CHROMOSOME ABERRATIONS PRODUCED BY 5-BROMODEOXYURIDINE WITH CONCURRENT EXPOSURE TO LONG WAVELENGTH UV IN ZEA MAYS ROOT TIP CELLS

Abstract

The influence of bromodeoxyuridine (BrUrdR) on the pattern and level of chromosome damage in Zea mays L. root tip cells is described. In some experiments long wavelength ultraviolet light was employed to convert the bromodeoxyuridine in DNA to its photoproduct. BrUrdR treatment produced a marked decrease in the mitotic index and a high proportion of the mitotic cells bore chromosome damage. Following a BrUrdR treatment of 5 h the proportion of damaged cells increased from 20% to 60% during the 20 h following treatment; then the proportion decreased sharply to less than 20%. Root tips treated as above followed by an exposure to long wavelength ultraviolet radiation (UV) had a proportion of damaged cells (80% at 20 h) only slightly greater than those not exposed to UV up to 20 h after treatment. Unlike the unirradiated BrUrdR substituted root tips, the proportion of damaged cells remained high 25 h after treatment. Furthermore, the spectrum of chromosome aberrations differed between irradiated and unirradiated BrUrdR substituted cells. Root tips exposed to long wavelength UV alone showed some damage that was limited to a stage in the cell cycle of irradiated root tips. Analysis of the BrUrdR treated corn DNA by cesium chloride density centrifugation showed that BrUrdR substitution for thymidine in DNA was extensive. Further experiments demonstrated that a large BrUrdR pool was not carried into the rounds of replication following BrUrdR removal from the medium. Nevertheless a small pool of halogenated pyrimidine was observable after BrUrdR removal from the medium.