The introduction consists of a review of the current evidence concerning the effects of near-ultraviolet radiation on cells, with particular emphasis placed upon possible effects on cell membranes. The experimental work, the broad aim of which is to expand existing knowledge of the effects of near-ultraviolet radiation that may lead to cell lethality, has centred upon the irradiation of a DNA repair-proficient Escherichia coli K-12 strain, SR385, using both monochromatic and broad-band sources. The work is divided into five parts. Chapter 1 indicates that broad-band near-ultraviolet irradiation of SR385 induces a sensitivity to inorganic salt, which is largely recoverable by holding treated cells in a complex recovery medium. By using various metabolic inhibitors, the recovery process has been related to a return of normal membrane functions. Chapter 2 describes an action spectrum, from 254-405nm, for ultraviolet radiation-induced salt sensitivity, and shows that this effect is important only at wavelengths above 310nm. The third part of the experimental section describes a more direct means of measuring ultraviolet radiation-induced membrane damage by the detection of leakage of radioactive labels from treated cells. An action spectrum, from 254-405nm, determined for 86 rubidium leakage, indicates that membrane damage may be important in near-ultraviolet (but not far-ultraviolet) radiation-induced cell lethality. Chapter 4 describes the effect of the phase of growth of the cell in determining its senstivity to near-ultraviolet radiation. The final chapter comprises a preliminary investigation into the effects of membrane damage in influencing the assessment of mutagenesis by near-ultraviolet radiation, by reversion to prototrophy. The data obtained in each section have been discussed in the context of current published concepts regarding the induction and repair of damage in cells by ultraviolet radiation.
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