Chromatid Aberrations inTradescantiaPollen Tubes Induced by Monochromatic X-rays of Quantum Energy 3 and 1·5 keV

SummaryMature pollen of Tradescantia paludosa and T. bracteata was irradiated with monochromatic x-rays of quantum energy 3 kev and 1·5 kev. Chromatid aberrations were scored at metaphase of the pollen-tube mitosis (second post-meiotic mitosis).It was found that: (1) 1·5 kev x-rays are efficient in producing aberrations; (2) the yield of aberrations with 3 kev x-rays is linearly proportional to dose; (3) the oxygen dose-modification factor with 3 kev x-rays is about 3 for true aberrations and 1·8 for single gaps.It is concluded that there is no longer any basis for the estimate that some 17 ‘ionizations’ are required for efficient ‘breakage’ of a chromatid. Instead, most of the facts are explicable in terms of ‘breakage’ by a single energy-loss event in a micro-structure of a chromatid, for example, a short length of a single macromolecule of DNA.