Causes of Cell Death Following Ultraviolet B and C Exposures and the Role of Carotenes

Abstract— Ultraviolet B radiation (wavelength 290–310 nm) does not induce any specific lethal effects in the fungus Phy-comyces blakesleeanus , according to a heterokaryon test that responds to the nature of the lethal damage. This agent is about 10 times less lethal than UVC radiation from germicidal lamps (254 nm), but it kills cells through the same photoreactivable lesions, due to the UV absorption of DNA. Carotenes do not protect Phycomyces against UV damage, either B or C, lethal or not. This was shown by Darwinian competition experiments between strains containing very different carotene concentrations and between strains containing similar concentrations of different carotenes (phytoene, lycopene, β-car-otene). A shading effect of carotenes against UV radiation is likely, but it was insignificant under the conditions of the experiments.