Studies on the Cellular Basis of Radiation Lethality

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Abstract
The experimentally verified model proposed by Lange and Gilbert (1968) quantitatively relates the parameters of the planarian mortality curve to those of the neoblast (planarian stem cell) survival (of reproductive integrity) curve. By use of previously measured values of the constants of the model and the mortality parameters of the members of the Dugesia lugubris auto- or allopolyploid series (2n, 3n, 4n), the neoblast survival curves are determined, and the first direct comparison of the effects of polyploidy on radiosensitivity in animal cells is made. No significant effect of polyploidy on radiosensitivity (D0) was found. The significantly lower survival of triploids with respect to diploids was found to be due to extrapolation number differences. These differences contradict those predicted by target theory. The implications of these findings are also discussed in terms of energy absorption per cell and per chromosome.