Effects of 8-methoxypsoralen and near ultraviolet radiation on the survival of the lower eukaryote D. discoideum

Seven axenic wild-type and repair-deficient mutant strains of the cellular slime mold Dictyostelium discoideum have been treated with the furocoumarin 8-methoxypsoralen (8-MOP) up to 50 μg/ml and then exposed to near ultraviolet light (UVA 320-400 nm) up to 21 kJ/m2. Fluence-response survival curves exhibit shoulders at lower fluences and an exponential lethal response at higher fluences. Neither the psoralen alone nor the irradiation alone produced any measurable lethal effect. Wild-type strains, which show resistance to 254 nm UV and gamma radiation, also show resistance to psoralen plus UVA. The moderate sensitivity of a rad D repair-deficient mutant strain and the extreme sensitivity of a plus rad B mutant strain to 8-MOP plus UVA parallel their responses to UV and gamma radiation. However a rad C mutant which is sensitive to UV, exhibits wild-type response to photoactivated psoralen. (author)