Effects of Hydration on X-Ray Sensitivity in Hordeum

Abstract

Shortly after Stadler (1) conducted his classical experiments with barley seeds showing that X-rays could induce mutations in plants, one of his students, Tascher (2), demonstrated that soaked barley seeds were more sensitive to X-rays than dry seeds. Since that time wet and dry seeds have been irradiated by numerous workers (Gelin, 3; Gustafsson, 4; Wertz, 5; Froier and Gustafsson, 6), and it has become widely accepted in radiobiology, primarily as a result of the studies with seeds, that, at the cellular level, as the water content of a biological system increases, so also does its sensitivity to X-rays (cf. 46a). The studies with soaked and dry seeds were conducted mostly during the 1930's and early 1940's when many workers considered that radiation-induced events were largely or solely a result of the direct absorption of energy by a sensitive site. Little attempt was made to clarify or interpret the nature of the modification of the radiosensitivity that occurred when water was added to seeds. However, in the 1940's when the was rediscovered (cf. Mottram, 7, 8) through the demonstration in a variety of organisms (9-12) that X-radiation in the presence of oxygen increased radiosensitivity, biologists began seriously considering the likelihood of the existence of other mechanisms by which radiation affected living tissues-other, that is, than by the direct absorption of energy at a sensitive site. The fact that radiation chemists early postulated the production of active radiation products from the radiodecomposition of water served to emphasize this possibility (13-20). Thus it developed that the theory of the indirect effect of X-rays came into prominence. This theory has as its basic tenet the concept that much radiation damage is mediated by active radicals, or other chemical entities, that are produced by radiation and that those radicals may be transported more or less distance in the cell to produce a detectable biological event-presumably, for the most part, by chemical modification of macromolecules. Additional support for the indirect action theory came from the findings that