EFFECTS OF 8‐METHOXYPSORALEN AND NEAR ULTRAVIOLET RADIATION ON THE SURVIVAL OF THE LOWER EUKARYOTE D. Discoideum

Abstract

Seven axenic wild-type and repair-deficient mutant strains of the cellular slime mold Dicryusrelium discoideum have been treated with the furocoumarin 8-methoxypsoralen (8-MOP) up to 50 pgirne and then exposed to near ultraviolet light (UVA 320-400 nm) up to 21 kJlm2. 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 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.

OXYGEN EFFECT IN SURVIVAL OF Dictyostelium discoideum TREATED WITH NEAR ULTRAVIOLET RADIATION

“…Previously published UVA survival data for cellular slime molds extended only to 21 kJ rn-' and did not show any lethal effects (Graetzer and Morrison, 1985). When the UVA emission from the lamp was absorbed by a red filter (Corning 2-60) which only tranrmitted wavelengths longer than 600 nm, survival was nearly 100% (Fig.…”

“…1) and still had a shoulder on the survival curve. In striking contrast the cytotoxic effects of gamma rays (Deering ef al., 1970), UVC (Welker and Deering, 1979), methyl methanesulfonate (Podgorski and Deering, 1980) and photoactivated psoralen (Graetzer and Morrison, 1985) decreased the survival of some mutant strains 5to 100-fold relative to wild-type strains. Also the extreme sensitivity of HPS5O was marked by the virtual absence of any shoulder on the survival curves.…”

“…Cell strains and growth. Cell strains, growth media and preparation of cells for exposure to UVA have been described in detail in an earlier report (Graetzer and Morrison, 1985). Identification of mutant strains was confirmed by measuring cell survival following exposure to 254 nm UV.…”

“…Assay for cell survival. The plating procedures used here for measuring survival have been described previously (Graetzer and Morrison, 1985).…”