Cytological effects of phenylnitrosamines—III. The effect on X-ray sensitivity at low oxygen tensions

Abstract

A number of agents structurally or functionally related to cupferron have been studied for their ability to enhance the frequency of chromosomal aberrations produced by X-rays in the presence of 1 per cent oxygen in the root-tips of Vicia faba. A marked enhancement was obtained only with agents which inhibited bean-root respiration. In experiments with the respiratory inhibitor carbon monoxide, the X-ray dose necessary to produce a given frequency of aberrations in the absence of oxygen was about 2.3 times as high as that which produced the same effect in the presence of 1 per cent oxygen. The carbon monoxide effect was light-reversible; no enhancement was obtained when the roots were exposed to strong light during irradiation and carbon monoxide treatment. Both cupferron and carbon monoxide enhanced X-ray sensitivity only when they were present before and during irradiation. Post-treatments with these agents did not have any influence on the frequency of aberrations produced by a given X-ray dose. The frequency of aberrations produced by 108 r of X-rays was almost doubled when the change from 1 per cent oxygen in nitrogen to 1 per cent oxygen in carbon monoxide was made 70 sec before irradiation. In order to be fully effective, the CO-treatment was started between 2 and 5 min before irradiation. These results support the hypothesis that cupferron and other respiratory inhibitors enhance the X-ray sensitivity of bean roots at low oxygen tensions because they prevent the formation of an oxygen gradient in the roots. A comparison between the cytological and physiological effects of cupferron, and those of some other agents which are structurally or functionally related to it, is presented in tabular form.