Induction of Chromosome Aberrations by Very Short Tracks at Different Stages of the Cell Cycle

Ultrasoft X rays of photon energy ≤1 keV have been previously observed to be highly efficient in producing biological damage in mammalian cells despite the very short track length of the electrons which these X rays produce within the cells. A large linear component of dose response has been observed for cell inactivation, mutation and chromosome aberration induction. This was found even for induction of exchange aberrations, for which, it is conventionally assumed, two separate points of damage are required. To investigate further the formation of aberrations by very short tracks (≤7 nm) at various stages of the cell cycle, asynchronous BHK Syrian hamster cells were irradiated with 0.28 keV carbon K characteristic ultrasoft X rays (and 250 kV hard X rays for comparison) and each mitotic spread classified into one of seven sub-phases of the cycle according to a recently developed method and key for KG stained cells. For all aberration types together, X rays from carbon were found to be much more effective than hard X rays. Further analyses and subdivision into aberration types are required before detailed implications can be drawn.