The Role of Oxygen Concentration in Determining the Effectiveness of X-Rays on the Action of a Specific Gene in Drosophila Melanogaster

Abstract

The genetic stocks used were a suppressor-erupt stock, Su-er bw; st er, and a wild-type stock, Oregon-R. It was known that when embryos had been irradiated with 1000 r units of X-rays, the Su-er stock had yielded 65.9% of extreme erupt and 95.7% of all grades of erupt in the adults, whereas the wild stock had yielded 3.4% of extreme erupt and 38.1% of facet disarrangements of the eyes. Eggs were collected over a 2-hr. period and X-rayed with 1000 r units at 10 [plus or minus] 1 hr. of embryonic development. The eggs were placed in a lucite chamber for irradiation, and the gases used (pure N2; 10% O2 / 90% N2; air; pure O2) were allowed to flow through the chamber during treatment. Temperatures during treatment were 24[degree] to 26.5[degree]C, and before and after treatment 25 [plus or minus] 0.5[degree]C. After treatment the eggs were kept in petri dishes for 24 hrs. to get hatching counts, then transferred to culture bottles and kept at 25[degree]C. In both stocks the frequency of erupt was affected by the concn. of O2 during irradiation; in the wild stock extreme erupt was reduced from 3.48% at 20% O2 (air) to 0.57% at 0% O2, and in the Su-er stock from 82.98% in air to 5.47% in the absence of O2. At 10% O2 both stocks showed frequencies of extreme erupt halfway between those at 0% O2 and 20% O2, and at 100% O2 there was only a slight increase in the frequency of extreme erupt over that at 20% O2. Irradiation in O2 did not seem to increase mortality during the embryonic period, but the larval and pupal stages showed a steady increase in mortality with increasing O2 concn. In 100% O2 approx. 95% of the Su-er individuals and 70% of the wild-type individuals were killed, whereas in 100% N, relatively few or no individuals were killed during the larval-pupal periods. Development was delayed after treatment in O2 but was normal after treatment in No. A high incidence of melanotic tumors was observed in the 3d larval instar of individuals treated with 1000 r units of X-rays in air at 10 [plus or minus] 1 hr. of embryonic development, with a frequency of 10% for the wild Oregon-R. stock and 82.0% for the Su-er stock. In both stocks the frequency of tumors varied with concn. of O2 similar to the frequency of erupt. There was no evidence that high mortality rates were caused by the development of tumors. Exposure of embryos to various O2 concns. without irradiation produced no observable deviations from normal development. The mortality and induction of tumors in individuals irradiated in O2 as embryos were believed due to cytoplasmic effects, since they paralleled the effect on Su-er which does not involve mutation, and since death occurred chiefly in the late third instar larvae or in the pupae, whereas dominant lethal mutations or inviable chromosomal aberrations affect the egg stage.