EVIDENCE FOR THERMAL REACTIONS FOLLOWING EXPOSURE OF DIDINIUM TO INTERMITTENT ULTRAVIOLET RADIATIONS

Abstract

Injury to D. nasutum from exposure to UV radiation appears as a slowed division rate, followed in more severe cases by a stasis, or stoppage of division, usually after the second post-treatment division. For a given dose, injury is increased by decreasing the intensity of irradiation, suggesting thermal reactions following an initial photochemical reaction, as a causative factor. Thermal reactions are suggested since, for a given dose of UV, injury is increased if (1) the dose is administered intermittently instead of continuously; (2) the dark period between flashes is lengthened; (3) the treatment is given at a higher temperature. These results are qualitatively comparable to those seen in studies of photosynthesis using flashing light. Quantitative differences are discussed.