A New Approach to the Mathematical Theory of the Action of High-Energy Radiation on Single Cells: I. Formulation of the Theory

Abstract

The understanding of the mechanism of the interaction between radiation and living matter has been greatly promoted by radiation experiments on unicellular organisms. Among these the yeast cell plays an important role, partly because of its availability in various ploidies, from haploid to tetraploid (1). The following discussion is centered around the yeast cell, but its domain of applicability is believed to extend to other microorganisms. Yeast cells of different ploidy respond very differently to radiation. Haploid yeast shows an exponential survival curve, whereas diploid, triploid, and tetraploid yeast exhibit sigmoid survival curves (2-11). This has been interpreted as strong evidence that the lethal effect of high-energy radiation is of genetic origin. The details of the interaction between radiation and genetic material still constitute one of the major problems. The different possible ways in which this interaction can take place may be divided in two main groups, sometimes labeled direct action and indirect action, respectively (2, 4, 12). The latter is sometimes called diffusion model or migration model (3, 4). By direct action is meant that the radiation ionizes or excites molecules in the genetic material through the electric fields of the charged particles of which the radiation consists, or which are produced by the radiation. The direct action has been treated extensively by Lea (13) and by Timofeeff-Ressovsky and Zimmer (14). The indirect action, on the other hand, explains the genetic effects of radiation by postulating that the ultimate genetic damage is done by certain chemical agents, which in their turn are the indirect products of the radiation. We shall call these agents intermediaries. Speculations as to the nature of these intermediaries have