Radiation Sensitivity of Tradescantia Microspore Chromosomes to a Second Exposure of X-Rays

Abstract

Tradescantia microspores were irradiated with 400 r of x rays and 2 days later with 50, 70, or 100 r. The cells were fixed and stained 23 to 27 hours after the second exposure. The first exposure produced only chromosome aberrations, and the second exposure produced only chromatid aberrations. The frequency of cells with chromatid aberrations in the cells which had been subjected to 400 r of x rays was much higher than in cells which had received only 50, 70, or 100 r, indicating that the irradiation of the cells at the resting stage made the chromosomes more sensitive to irradiation at prophsse. Irradiation at the early resting stage resulted in some increase in chromosome aberration frequency by the second dose given at the late resting stage, but the results are of doubtful statistical significance. An analysis of microspores which had been given 400 r followed by 50, 70, or 100 r shows that the cells with no chromosome aberrations induced at the resting stage were twice as sensitive to irradiation at prophase as the cells which contained one or more chromosome aberrations which had been induced at the resting stage, and microspores with only one chromosome aberration weremore » more sensitive to irradiation at prophase than microspores with two chromosome aberrations, although all cells had been subjected to 400 r of x rays at the resting stsge. (auth)« less