DIFFERENT MECHANISMS OF INACTIVATION DEPENDING ON DOSE AND PHYSIOLOGICAL PARAMETERS - DISCREPANCIES BETWEEN THEORETICAL INTERPRETATION OF DOSE EFFECT CURVES AND BIOLOGICAL FACTS

The fate of individual cells of the haploid fission yeast Schizosaccharomyces Pombe has been studied after irradiation with different dosis and milieu conditions and in some cases also the fate of the descendents. Colonies can include early and late inactivated cells (early and late mosaics) while cells can be inactivated in 1, 2, 3 or more cells-stage. At least 10 classes of damage can be distinguished. The proportion of these classes are variabel - depending on dose, metabolic conditions and O2-tension. With low doses early-death is frequent, while with high doses late death is increased. In connection with other observations we concluded that with low doses the damage of nucleus preponderates while with increasing doses the cytoplasmatic damage begins to be important, which can be easily influenced. The analysis of the probability of division after irradiation demonstrated a sharp augmentation of the probability of division-inactivation after the first division. This augmentation of the division-inactivation maintains over the 8. division. The splitting of the survival curves in different individual curves related to damage mechanisms makes the valuability of interpreting total survival curves doubtful. © 1969 Springer-Verlag.