FUNCTION OF CAROTENOIDS IN PROTECTION OF <i>RHODOTORULA GLUTINIS</i> AGAINST IRRADIATION FROM A GAS LASER

Abstract

Abstract— The sensitivity of older cells of Rhodotorula glutinis containing a high concentration of carotenoids was compared with young cells containing little visible pigmentation. The younger cells died faster, suggesting that the carotenoids protected. Further, cells grown in the presence of diphenylamine, an inhibitor of carotenoid syntheses, were more susceptible than were normally grown cells. A carotenoidless mutant, isolated after exposure of the wild strain to u.v. light, was more susceptible to lethal photosensitization than the wild strain. The difference in sensitivity, however, was not as great as between old and young cultures of the wild strain. Young cultures of the white mutant were more susceptible to death than were older cultures, therefore, sensitivity is related to age as well as to carotenoid content. The difference in sensitivity was increased between the white mutant and the wild strain when lower light intensities were used. At 10 mW the difference in the lag period was 60 min, while at 30 mW the difference was only 10 min. The lag period was also dependent on the temperature at which cell suspensions were irradiated. At 3°C, no death occurred in 1 hr at 27 mW with either wild or mutant strains. The lag was progressively shorter with increased temperature. The rate of death, however, was apparently not affected by differences in temperature. An analysis of the carotenoids from the irradiated cells did not show any detectible changes even though it was demonstrated that β‐carotene could be bleached when irradiated in vitro in the presence of toluidine blue.