Effects of 163-nm Vacuum uv Radiation on the Initiation of Mitosis in Physarum polycephalum

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Abstract
Advantage was taken of the limited penetration of vacuum UV radiation to dissect the role of cellular materials in the mitotic triggering mechanism in P. polycephalum. Mitotic delays were measured after exposure of plasmodia to 163 nm UV radiation at various times in the cell cycle. A marked delay was observed only when the cell was irradiated in late G2, the maximum delay arising from irradiation at the end of G2. This delay pattern was different from those which have been observed for X-rays, .gamma.-rays and 254 nm far-UV radiation. Considering the very limited penetration of 163 nm UV radiation, it was concluded that the delay must be caused by damage in the surface layer of the plasmodia. The occurrence of maximum delay at the end of G2 suggests that the damaged site was intimately related to mitotic triggering.