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

Summary

Mature 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.