Absence of Detectable Fractionation Effects in Tradescantia Somatic Mutations for an X-Ray Dose of 5 rad

Abstract

Two experiments have been performed to determine directly and with statistical accuracy the presence or absence of detectable fractionation effects for pink somatic mutations in Tradescantia stamen hairs. The experiments were done at X-ray doses low enough to fall along the strongly linear segment of the linear-quadratic dose-response curve. From previous work it was known that pink mutation frequency is about 34% less if exposed to a 35 + 35-rad dose. This dose falls along the strongly quadratic segment of the dose-response curve. In the present experiments, involving over 836,000 stamen hairs, the mutation frequency resulting from 2.5 + 2.5 rad of X rays with 5 hr between doses was the same as that resulting from an acute dose of 5 rad. It is suggested that fractionation effects may not occur in somatic mutations at still much lower X-ray dose levels.