Induction of Structural Chromosome Changes by Visible Light

Abstract

IT has been known since the beginning of this century that visible light is able to induce inhibitory and lethal effects on living organisms when oxygen and some sensitizing substance (which absorbs the light) are present. This phenomenon has been called ‘photodynamic action’. The biological effects are believed to be due mainly to a photosensitized oxidation of organic material¹. The fact that mutations can be induced photodynamically in microorganisms has been shown by Döring² and Kaplan^3–5. Previous studies have failed to demonstrate the production of structural changes in chromosomes among the effects induced in plant root-tips by visible light in the presence of some sensitizing substance^6,7. The dyes used in these studies, eosin and neutral red, have no particular affinity for the cell nucleus. It seems reasonable to assume that in order to induce changes in the genetic material the light has to be absorbed by dye molecules present inside the cell nucleus. Therefore, acridine orange, which, like a number of other acridine derivatives, has a high affinity for nucleic acids^8,9, was chosen as the sensitizing substance in the present study of the effect of visible light on chromosome structure in the root-tip cells of the broad bean, Vicia faba.