Photoreversal of Nuclear and Cytoplasmic Effects of Short Ultraviolet Radiation on Paramecium Caudatum

Abstract

1. Irradiation with three short ultraviolet (UV) wave lengths, 226, 233, and 239 mµ rapidly immobilizes Paramecium caudatum, the dosage required being smaller the shorter the wave length. 85 per cent of paramecia immobilized with wave length 226 mµ recover completely. Recovery from immobilizing doses is less the longer the wave length. 2. Irradiation continued after immobilization kills the paramecia in a manner which is markedly different for very short (226, 233, and 239 mµ) and longer (267 mµ) wave lengths. 3. An action spectrum for immobilization in P. caudatum was determined for the wave lengths 226, 233, 239, 248, and 267 mµ, and found to resemble the absorption of protein and lipide in the wave length region below 248 mµ. Addition of these data to those of Giese (1945 b) gives an action spectrum resembling the absorption by albumin-like protein. 4. Division of P. caudatum is delayed by doses of wave lengths 226, 233, and 239 mµ which cause immobilization, the longest wave length being most effective. 5. Immobilization at any of the wave lengths tested (226, 233, 239, 248, 267 mµ) is not photoreversible when UV-treated paramecia are concurrently illuminated. 6. Division delay resulting from immobilizing doses of 226, 233, and 239 mµ is photoreversible by exposure to visible light concurrently with the UV. 7. Division delay induced by exposure to wave length 267 mµ is reduced by exposure to visible light applied concurrently with UV or immediately afterwards. 8. The data suggest that the shortest UV wave length tested (226 mµ) affects the cytoplasm selectively, because it is absorbed superficially as indicated by unilateral fluorescence in UV. Consequently it immobilizes paramecia rapidly but has little effect on the division rate because little radiation reaches the nucleus. 9. The data support the view that nuclear effects of UV are readily photoreversed but cytoplasmic effects are not.

Enterococci in the Environment

“…Major mechanisms of sunlight damage to microorganisms include the direct absorption of UV light by DNA or the indirect effect of the formation of endogenous and exogenous reactive oxygen species. The ability of DNA to absorb UV light was discovered in 1929 (117), leading to studies of the mechanism of UV damage to DNA and microbial inactivation (33,97,189). Many mesocosm studies have noted the germicidal effect (defined as a loss of culturability) of sunlight on enterococci (77,112,187,255,286,(306)(307)(308) (Table 2); however, the reported time required to achieve a 90% reduction in the concentration (T 90 ) (equivalent to a 1-log reduction) varies widely according to geographic and seasonal factors and the experimental design (e.g., the source of the inoculum or physicochemical properties of the water).…”

Shedding Light on the DNA Damage Checkpoint

“…The importance of pyrimidine dimers in UV-induced division delay is supported by the observation that the delay can be reduced by exposure of cells to visible light in a number of model systems. [10][11][12] The mitigating effect of visible light on the survival of E. coli and budding yeast is known to result from the splitting of pyrimidine dimers by photolyase, [13][14][15] and it seems likely that the observed reduction in cell division delay is due to the same mechanism.…”

Contractile Vacuoles and Associated Structures: Their Organization and Function

“…Increases in contractile vacuole activity following low doses of ultraviolet radiation (Tchakhotine, 1936) might also be attributable to changes in membrane permeabilities. However, the arrest of vacuolar expulsions upon exposure to higher doses of ultra-violet radiation is probably attributable to factors other than osmotic balance (Shirley & Finley, 1949; Brandt & Giese, 1956; Mayer & Iverson, 1957).…”