Respiration and Radiosensitivity of Broad Bean Roots

Abstract

IN the root-tips of the broad bean, Vicia faba, potassium cyanide, hydrogen sulphide and cupferron (the ammonium salt of nitrosophenylhydroxylamine) increase the frequency of chromosome aberrations produced by a given dose of X-rays at very low oxygen pressures^1–3. In the case of cupferron at least, the effect on radiosensitivity seems to be a result of its inhibitory action on the respiration of bean root tips³. The fact that oxygen enhances the radiosensitivity of the root-tip chromosomes of Vicia faba has been known since the studies of Thoday and Read⁴. When the roots are respiring normally an oxygen effect does not become evident until the concentration of oxygen in the gas phase exceeds 3 per cent, apparently because at lower concentrations oxygen is removed by respiration in the outer cells of the root, so that completely anaerobic conditions prevail in the central parts. When respiration is inhibited, oxygen is able to diffuse into the cells of the whole meristem, even in cases when the oxygen concentration outside the root is very low. That this is the correct explanation of the increased frequency of aberrations obtained in the presence of cupferron is indicated by the fact that cupferron has no marked influence on radiosensitivity in the complete absence of oxygen³.