Action Spectrum For Photoreactivation Research Articles

Photoreactivation of UV‐lnactivated Spores of Trichoderma harzianum

Abstract— Photoreactivation in the filamentous soil fungus Trichoderma harzianum is of interest because its blue, UVA photoreceptors (cryptochromes) may share homology with DNA photolyases. Furthermore, this organism antagonizes, by mycoparasitism, a number of soil‐borne pathogens. Photoreactivation is thus important as one of the factors that may contribute to survival in the field. Exposure of asexually produced spores (conidia) to UVC inhibits germination. Nongerminating spores either do not swell or are inhibited later in germination, swelling but failing to put out a germ tube. Both types of inhibition can be reversed by photoreactivation with visible and UVA (320‐400 nm) light, restoring high germination percentages. Conidia of mutants lacking the normal greenish pigmentation are more sensitive to UVC (200‐280 nm) than wild‐type conidia but photoreactivation still occurs. The action spectrum for photoreactivation indicates that T. harzianum has a DNA photolyase with a pterin as second chromophore. The most effective wavelengths for photoreactivation correspond to valleys, rather than peaks, in the action spectrum for photoinduction of sporulation. Furthermore, mutants with defects in photoinduction of sporulation (dimY) are not defective in photoreactivation. Induction of sporulation and DNA photorepair, while sharing parts of the blue/UVA spectrum, are different, by spectroscopic, kinetic and genetic criteria.

PHOTOREACTIVATION OF Halobacterium halobium: ACTION SPECTRUM AND ROLE OF PIGMENTATION

Abstract— An action spectrum for photoreactivation was measured with Halobacterium halobium R1m1 to prove a role of carotenoid pigments in photoreactivation of the bacteria. The action spectrum obtained showed a main peak at 435 nm and a minor peak at about 325 nm. The action spectrum was similar to that of Streptomyces pigment (Eker et al., 1981) suggesting that the chromophore of the photoreactivating enzyme in Halobacterium halobium is 8‐OH‐5‐deazaflavin. The minor peak may be due to photochemical cleavage of a pyrimidine6–4 hetero adduct. The result indicates that carotenoid pigments do not play a positive role in enhancing photoreactivation. This was confirmed also by comparing the efficiency of photoreactivation at 465 nm among three strains of Halobacterium halobium having different carotenoid pigments; R1m1. R1 and W5002–1.

The action spectra for photoreactivation and photorepair in ICR 2A frog cells.

Abstract— Action spectra for photoreactivation (enhancement of colony forming ability) and photorepair (monomerization of pyrimidine dimers in DNA) were obtained for ICR 2A frog cells over the334–577 lira range. These spectra were very similar with peaks at 435 nm and little effectiveness at wavele.

Some phylogenetic implications of action spectra for photoreactivation of ultraviolet-inactivated yeasts.

Action spectra for photoreactivation of ultraviolet-inactivated cells of representative species of five genera of yeasts indicate that the spectral requirements for photoreactivation are characteristic for individual genera and may be useful data in analyses of the systematics of yeasts.

ACTION SPECTRA FOR UV INDUCTION AND PHOTOREVERSAL OF A SWITCH IN THE DEVELOPMENTAL PROGRAM OF THE EGG OF AN INSECT (SMITTIA)*

Abstract— An action spectrum was established for the induction by ultraviolet (UV) radiation of the aberrant body segment pattern ‘double abdomen’ in the egg of the Chironomid midge Smittia. The action spectrum shows a peak at 285 nm wavelength, a shoulder at 265 nm, a slight increase from 245 to 240 nm, and a steep decline towards 300 nm. Corrections for wavelength‐dependent shielding within the egg result in transformation of the shoulder at 265 nm into a minor peak. These results are compatible with the assumption that a nucleic acid‐protein complex is involved in the initial photoreaction. This assumption is supported by the fact that the UV induction of the aberrant body segment pattern ‘double abdomen’ in the egg of Smittia is photoreversible. Wavelengths effective in this photoreversal range from 310 to 460 nm, with a peak at 440 nm. These spectral characteristics agree with action spectra for photoreactivation in other systems. Indirect photoreactivation does not occur in the egg of Smittia under the conditions of the experiments. Photoreversal with 440 nm radiation at high dose rate is temperature‐dependent. The results support the assumption that the molecular basis for photoreversal in the egg of Smittia is similar to the predominant molecular mechanism of direct photoreactivation in other systems. Targets possibly involved in the UV induction of the ‘double abdomen’ are discussed.

Deoxyribonucleic Acid Photoreactivating Enzyme from Escherichia coli: PURIFICATION AND PROPERTIES

Abstract DNA photoreactivating enzyme has been purified from Escherichia coli B and from induced cells of an E. coli strain containing a lysogenic bacteriophage carrying the gene for photoreactivation. The final preparations appear homogeneous by the criteria of presence of one band after electrophoresis on polyacrylamide gels under nondenaturing conditions and of constant specific activity in enzyme fractions eluted from hydroxylapatite. The enzyme has an apparent monomer molecular weight between 40,000 and 46,000 and tends to aggregate in solution. The pH optimum under the present assay conditions is 7.2. The action spectrum for photoreactivation by the purified enzyme has a maximum in the same region and the same spectral shape as the action spectrum obtained for E. coli cells in vivo.

Action spectra for ultraviolet killing and photoreactivation in the blue-green alga Agmenellum quadruplicatum.

Abstract— The action spectrum for photoreactivation has been determined in a coccoid blue‐green alga, Agmenellum quadruplicatum. The spectrum is rather similar to that recorded for Streptomyces griseus conidia, with some suggestion of a little more structure. The action spectrum suggests possible carotenoid involvement; however, no other evidence for this could be found. The action spectrum for u.v. killing is also broad with some evidence of fine structure. The possible implication of tetrahydropteridines or c‐phycocyanin as chromophores in the region 240–300 nm, along with DNA, is pointed out.

Photoreactivation action spectrum of tobacco mosaic virus-ribonucleic acid inactivated by U.V. radiation.

Abstract— Initially photoreactivation of irradiated (2537 Å) nucleic acid on pinto bean increases linearly with time of illumination with white light of 250 ft‐c. Maximum amounts of photo‐reactivation depend on the quality of light used. The action spectrum shows a peak in the ‘black light’ region, where the greater amount of photoreactivation is found, and a shoulder in the blue light region. Maximum repair is obtained with ‘black light.’ Photoreactivation does not occur at wavelengths above 550 nm. Photoprotection by illumination of leaves prior to inoculation by irradiated RNA was not found. The action spectrum for photoreactivation does not resemble the action spectrum for photosynthesis.