Radiation-Induced Chromosome Aberrations and Loss of Reproductive Integrity in Tradescantia

Much information has been accumulated in recent years on the loss of reproductive integrity in irradiated populations of animal cells. Data have been acquired mainly from studies of cell populations cultured in vitro, and although such results can vary, owing to different culturing conditions (1, 2), a comparison with the few results available from in vivo studies (3-5) has shown good agreement between the two sets of data. With higher plant cells in vitro studies have not been technically feasible up to now, and it has been possible only to estimate radiationinduced loss of reproductive integrity either by studying the sequence of changes in the histological structure of an organized meristematic region (6) or by following the patterns of recovery of growth in irradiated roots (7, 8). For most of these cell types-both animal and plant-the survival curves after X-ray and y-ray exposures are sigmoid, fitting the expression S = [1 (1 e-kD) ]m, where S is the survival at dose D, n is assumed to be the number of sites of one particular type which must be inactivated to sterilize the cell (extrapolation number), and m is the number of different kinds of site. The value of m is generally assumed to be 1, although this assumption has been disputed by Bender and Wolff (9) and by Bender and Gooch (1). 1/k or Do is the dose required to reduce the surviving fraction, S, to 0.37S, i.e., (e-'S) on the exponential part of the curve, and has been found to be between 50 and 300 r for most of the mammalian cells investigated and between 35 and 90 rads for Vicia faba (7, 8). Puck (10-12), on the basis of the good agreement of the mammalian cell survival curves to the equation