Abstract

By placing a layer of water vapor of near 100% relative humidity (20 to 30 Torr depending on room temperature) between cell samples (Saccharomyces cerevisiae) and a MgF/sub 2/ window at the end of the vacuum path of the photon beam, we were able to irradiate cells under wet conditions with vacuum-ultraviolet light (115 to 190 nm) using synchrotron radiation from an electron storage ring (0.3 GeV). A deuterium discharge lamp with a MgF/sub 2/ window was also utilized as a source of vacuum uv in a similar wavelength range. Survival decreased in a sigmoidal way. The induction of gene conversion (at trp5 locus) occurred by irradiation with synchrotron radiation to a much lesser extent on a survival basis compared with that by far-uv (254 nm) irradiation. The induction was, however, attributed to the far-uv component of synchrotron radiation based upon the observation of photoreactivation. A remarkable feature with vacuum-uv effects was that holding in liquid after irradiation brought about a drastic decrease of survival. Furthermore, the sensitivity to treatment after irradiation with toluidine blue (membrane-attacking agent) and visible light was found to be significantly higher in cells exposed to synchrotron radiation than to far uv. These results indicate thatmore » damage on or near the cell membrane is more important than that in the nucleus for cell inactivation by vacuum-uv radiation.« less

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