EFFECT OF NUTRITIONAL STATE AND OTHER CONDITIONS ON ULTRAVIOLET RESISTANCE AND PHOTOREACTIVATION IN YEAST

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Abstract
Yeast in the logarithmic phase of growth is much less sensitive than that just past the logarithmic phase. Yeast kept in salt solution in the absence of organic nutrients for 17 hours is more resistant than that just out of logarithmic phase. Kept in salt solution for 14 days, yeast becomes much more sensitive than logarithmic phase yeast. Supplying glucose to yeast which has been deprived of organic nutrients for a time markedly increases its resistance to UV radiations. Supplying yeast extract to yeast which had been deprived of a nitrogen source for several days greatly increases its resistance to UV radiation, while supplying an inorganic N source does not. In the absence of O2 yeast is about as sensitive to UV radiation as in air. In pure O2 its sensitivity to the radiation changes but little. Cyanide does not protect yeast against radiation injury. Irradiated yeast recovers from UV radiation injury to a considerable extent in the dark if suspended in phosphate buffer at 28[degree]C but not at 5[degree]C, but recovery is greater following illumination (photoreactivation). Photoreactivation declines soon after plating yeast on nutrient agar and much more rapidly at 28[degree]C than at 5[degree]C. Photoreactivation occurs equally well under anaerobic as under aerobic conditions.