CAUSES OF CELL-DEATH FOLLOWING ULTRAVIOLET-B AND ULTRAVIOLET-C EXPOSURES AND THE ROLE OF CAROTENES

Ultraviolet B radiation (wavelength 290-310 mn) does not induce any sp ecific lethal effects in the fungus Phycomyces blakesleeanus, accordin g to a heterokaryon test that responds to the nature of the lethal dam age, This agent is about 10 times less lethal than UVC radiation from germicidal lamps (254 nm), but it kills cells through the same photore activable lesions, due to the UV absorption of DNA. Carotenes do not p rotect Phycomyces against UV damage, either B or C, lethal or not, Thi s was shown by Darwinian competition experiments between strains conta ining very different carotene concentrations and between strains conta ining similar concentrations of different carotenes (phytoene, lycopen e, beta-carotene). A shading effect of carotenes against UV radiation is likely, but it was insignificant under the conditions of the experi ments.