Capacity For Photoreactivation Research Articles

Effects of Low Temperature on Spider Mite Control by Intermittent Ultraviolet-B Irradiation for Practical Use in Greenhouse Strawberries.

The application of ultraviolet-B (UVB) radiation to control spider mites is challenging as a key technology for integrated pest management (IPM) in greenhouse strawberries in Japan. To address this, concurrent use of phytoseiid mites and reduced UVB irradiance is desirable to ensure control effects in areas shaded from UVB radiation and to minimize the sunscald in winter, respectively. We designed experiments reproducing the UVB dose on the lower leaf surfaces in strawberry and evaluated the effects of intermittent UVB irradiation at midnight for practical application in the greenhouse and low temperature on the survival of the spider mite Tetranychus urticae Koch (Acari: Tetranychidae) and damage to the phytoseiid mite Neoseiulus californicus (McGregor) (Acari: Phytoseiidae). The midnight intermittent UVB irradiation effectively suppressed egg hatching and development of larvae of T. urticae, and the control effect was reinforced at 20°C (no eggs hatched at 0.13 kJ m-2 d-1) rather than, at 25°C (70.8% eggs hatched). In contrast, the hatchability of N. californicus eggs was unaffected by intermittent UVB irradiation at 0.27 kJ m-2 d-1 at 25°C and 20°C. However, residual effects of UVB irradiation to N. californicus eggs on survival of hatched larvae were seen, so that reducing the UVB dose is also advantageous for this phytoseiid mite. N. californicus showed a photoreactivation capacity, whereas their UVB tolerance was improved by prey species, suggesting the possibility of the improvement of phytoseiid mites by diet. The reduction of UVB dose and concurrent use of phytoseiid mites increase reliability of the UVB method in IPM strategies in strawberry greenhouse.

The Trichoderma atroviride cryptochrome/photolyase genes regulate the expression of blr1-independent genes both in red and blue light

Quantitative transcriptome analysis led to the identification of 331 transcripts regulated by white light. Evaluation of the response to white light in mutants affected in the previously characterized blue-light receptor Blr1, demonstrated the existence of both Blr1-dependent and independent responses. Functional categorization of the light responsive genes indicated the effect of light on regulation of various transcription factors, regulators of chromatin structure, signaling pathways, genes related to different kinds of stress, metabolism, redox adjustment, and cell cycle among others. In order to establish the participation of other photoreceptors, gene expression was validated in response to different wavelengths. Gene regulation by blue and red light suggests the involvement of several photoreceptors in integrating light signals of different wavelengths in Trichoderma atroviride. Functional analysis of potential blue light photoreceptors suggests that several perception systems for different wavelengths are involved in the response to light. Deletion of cry1, one of the potential photoreceptors, resulted in severe reduction in the photoreactivation capacity of the fungus, as well as a change in gene expression under blue and red light.

Factors affecting photoreactivation in UVB-irradiated herbivorous spider mite (Tetranychus urticae)

Ambient ultraviolet-B (UVB) radiation causes lethal damage to spider mites, and the extent of photochemical effects is determined by cumulative irradiance in the two-spotted spider mite, Tetranychus urticae. However, the LD50 values obtained using a UVB lamp were much lower than those elicited by solar UVB radiation. As solar radiation includes intense visible light and UVA, we assumed that a photoreactivation mechanism would play a role to survive under solar radiation. We assessed the capacity for photoreactivation in T. urticae eggs and larvae, and found that the efficacy of photoreactivation was determined by the cumulative irradiance of visible light (VIS) after exposure to UVB radiation. The wavelength range effective for photoreactivation went from UVA to green. Next, we found that an increased time lag between UVB and VIS radiation reduced the photoreactivation efficacy in eggs. In contrast, a time lag ≤4h did not affect that in larvae. We discussed the possibility that the timing of photoreactivation occurs related with phase-specific UVB vulnerability and outbreak symptoms due to UVB-induced DNA damage. Our results suggest that T. urticae depends on a photoreactivation mechanism, and that the photoreactivation efficiency probably caused the divergence in UVB impact between UV lamp and solar radiation.

High-energy pulse-electron-beam-induced molecular and cellular damage in Saccharomyces cerevisiae

The high-energy pulse electron beam (HEPE) is a new method for mutation breeding. Previously, we demonstrated that HEPE radiation improved thermotolerance and ethanol production of Saccharomyces cerevisiae. To investigate the influence of HEPE on yeast molecular and cellular damage, cells were separately treated with HEPE radiation at different doses (0, 200, 400, 600, 800, 1000, 1200 and 1400 Gy). Based on results obtained, protein leakage and diffusion of intracellular nucleotide and propidium iodide (PI) uptake assays showed that HEPE clearly enhanced the cell membrane permeability of yeast depending on the dose of exposure. Yeast cells treated with HEPE radiation had significantly elevated levels of DNA instability, as detected by the chromosome spreading assay. These results correlated well with the measurement of increased levels of chromosomal aberrations and apoptosis. Intracellular reactive oxygen species (ROS) and caspase 3 activity were also measured in HEPE-applied yeast cells. Caspase 3 appeared to be involved in HEPE-induced apoptosis. Use of dihydroethidium staining and confocal laser scanning microscopy (CLSM) showed increased levels of intracellular ROS as a consequence of augmented pulsing. Moreover, yeast cells retained some photoreactivation capacity when the dose of HEPE exposure was less than 600 Gy. Thereafter, the level of damage was too serious to repair. Thus, photoreactivation had a repair effect upon HEPE radiation-induced damage. The results of our studies provide a possible explanation for the molecular and cellular effects of HEPE radiation upon S. cerevisiae.

Characterization of Blue-light and Developmental Regulation of the Photolyase gene phr1 in Trichoderma harzianum

Blue light and development regulate the expression of the phr1 gene of the filamentous fungus Trichoderma harzianum. The predicted product of phr1, the DNA repair enzyme photolyase, is likely to help protect Trichoderma, which grows in the soil as a mycoparasite or saprophyte, from damage upon emergence and exposure to ultraviolet-c. phr1 is transiently expressed in mycelium and conidiophores after illumination. phr1 mRNA also accumulates in conidiophores during development and spore maturation. As no other genes displaying rapid, direct light regulation have been described previously in this organism, we have characterized the fluence and time dependence of phr1 induction, and its relation to sporulation and photoreactivation. Induction is transient following a pulse, and, with slower decay, in continuous light. This implies that the photoreceptor, transducers or response are capable of adaptation. About two-fold more light is required to induce phr1 than conidiation, but this difference is modest, so both responses could use the same or similar chromophore. Adenosine 3′:5′-cyclic monophosphate bypasses the requirement for light for sporulation, while atropine prevents sporulation even after photoinduction. Light regulation of phr1, however, is indifferent to both these effectors. Induction of photolyase expression behaves as a direct, rapid response to light, independent of the induction of sporulation. Indeed, illumination of mature spores increases their capacity for photoreactivation. Blue light seems to warn the organism against the harmful effects of short wavelengths, inducing phr1 expression and sporulation by pathways that are, at least in part, distinct.

Influence of infected cell growth state on bacteriophage reactivation levels.

Reactivation of UV-C-inactivated Pseudomonas aeruginosa bacteriophages D3C3, F116, G101, and UNL-1 was quantified in host cells infected during the exponential phase, during the stationary phase, and after starvation (1 day, 1 and 5 weeks) under conditions designed to detect dark repair and photoreactivation. Our experiments revealed that while the photoreactivation capacity of stationary-phase or starved cells remained about the same as that of exponential-phase cells, in some cases their capacity to support dark repair of UV-inactivated bacteriophages increased over 10-fold. This enhanced reactivation capacity was correlated with the ca. 30-fold-greater UV-C resistance of P. aeruginosa host cells that were in the stationary phase or exposed to starvation conditions prior to irradiation. The dark repair capacity of P. aeruginosa cells that were infected while they were starved for prolonged periods depended on the bacteriophage examined. For bacteriophage D3C3 this dark repair capacity declined with prolonged starvation, while for bacteriophage G101 the dark repair capacity continued to increase when cells were starved for 24 h or 1 week prior to infection. For G101, the reactivation potentials were 16-, 18-, 10-, and 3-fold at starvation intervals of 1 day, 1 week, 5 weeks, and 1. 5 years, respectively. Exclusive use of exponential-phase cells to quantify bacteriophage reactivation should detect only a fraction of the true phage reactivation potential.

Characterization of blue-light and developmental regulation of the photolyase gene phr1 in Trichoderma harzianum.

Blue light and development regulate the expression of the phr1 gene of the filamentous fungus Trichoderma harzianum. The predicted product of phr1, the DNA repair enzyme photolyase, is likely to help protect Trichoderma, which grows in the soil as a mycoparasite or saprophyte, from damage upon emergence and exposure to ultraviolet-c. phr1 is transiently expressed in mycelium and conidiophores after illumination. phr1 mRNA also accumulates in conidiophores during development and spore maturation. As no other genes displaying rapid, direct light regulation have been described previously in this organism, we have characterized the fluence and time dependence of phr1 induction, and its relation to sporulation and photoreactivation. Induction is transient following a pulse, and, with slower decay, in continuous light. This implies that the photoreceptor, transducers or response are capable of adaptation. About two-fold more light is required to induce phr1 than conidiation, but this difference is modest, so both responses could use the same or similar chromophore. Adenosine 3':5'-cyclic monophosphate bypasses the requirement for light for sporulation, while atropine prevents sporulation even after photoinduction. Light regulation of phr1, however, is indifferent to both these effectors. Induction of photolyase expression behaves as a direct, rapid response to light, independent of the induction of sporulation. Indeed, illumination of mature spores increases their capacity for photoreactivation. Blue light seems to warn the organism against the harmful effects of short wave-lengths, inducing phr1 expression and sporulation by pathways that are, at least in part, distinct.

Overproduction of SSB protein enhances the capacity for photorepair in Escherichia coli recA cells.

We studied photoreactivation in cells carrying the multicopy ssb+ plasmid. These cells overproduce single-stranded DNA-binding protein (SSB). Overproduction of SSB enhances the capacity for photoreactivation in recA bacteria but not in the recA+ background. It is suggested that, in recA cells, SSB binds to the dimer region of DNA and that this binding stimulates the process of photoreactivation. In recA+ cells, the same stimulation might be achieved by RecA protein.

Photoreversal of the ultraviolet radiation-induced disappearance of ATPase-positive Langerhans cells in the epidermis of Monodelphis domestica.

The present study was undertaken to explore the possible causes of ultraviolet radiation (UVR)-induced disappearance of ATPase-positive, epidermal Langerhans cells (LC). Monodelphis domestica was used because it has the capacity for photoreactivation of UVR-induced pyrimidine dimers in epidermal DNA. Single, 330 J/m2 (ears) or 500 J/m2 (back) UVR exposures (FS-40 sunlamps) reduced the numbers of ATPase-positive epidermal LC in M. domestica ears to approximately 15% of those in unirradiated ears and approximately 37% of those in unirradiated dorsal skin. Immediate 90-minute exposures to photoreactivating light (PRL, 320-400 nm) post-UVR reversed the effects of UVR, resulting in ATPase-positive LC numbers not being significantly different from controls. Exposure to PRL immediately preceeding UVR did not prevent ATPase-positive LC disappearance. The photoreactivation of UVR-induced ATPase-positive LC disappearance indicates that DNA damage (pyrimidine dimers) is involved in the loss of ATPase-positive LC.

A comparison of liquid-holding recovery and photoreactivation in halophilic and non-halophilic bacteria

The ability of the extreme halophile Halobacterium cutirubrum to recover from the effects of ultraviolet radiation during liquid holding in the dark in non-nutrient medium has been compared with that of (i) a moderately halophilic bacterium (NRC 41227) and (ii) Escherichia coli B. The photoreactivabilities of all three bacteria have also been studied. The extreme halophile was incapable of liquid-holding recovery in these conditions, in marked contrast to both E. coli B and the moderate halophile, and also failed to recover when held in nutrient medium in the dark. These results strongly support the hypothesis that H. cutirubrum lacks DNA excision repair. It was also found that ultraviolet-irradiated H. cutirubrum could be almost completely photoreactivated from any level of survival in the range 10 −4-80%, provided exposure to visible light was not delayed, whereas the moderate halophile resembled E. coli B and had a comparatively limited capacity for photoreactivation.

Loss of photoreactivability during liquid-holding in Escherichia coli WP2.

Abstract—Loss of photoreactivability during liquid‐holding occurs much faster in Escherichia coli WP2 than has been reported for another strain of B/r (Harm, 1968). The underlying mechanism considerably reduces the maximum photoreactivation attainable within 30 min. The addition of caffeine to UV irradiated strain WP2 prevents the loss of photoreactivation activity. Similarly, a uvrA mutant also fails to show this loss of photoreactivation capacity. These results are consistent with the view that in WP2 the initial steps of excision repair take place during liquid‐holding and that they can preclude photoreactivation at a high rate. But it remains to be elucidated why different strains of B/r differ with respect to this rate.

Culture conditions affect photoreactivating enzyme levels in human fibroblasts

Photoreactivation of pyrimidine dimers in mammalian cells occurs under our experimental conditions but has not been observed under conditions used by others. We have tested three possible differences in experimental procedures including dimer separation and analysis methods, illumination conditions and cell culture techniques. We show that our methods of dimer separation and analysis indeed measure cis-syn pyrimidine dimers and give results in quantitative agreement with the methods of others. We find that white light pre-illumination of fibroblasts from the xeroderma pigmentosum line XP12BE or of normal cells does not affect the cellular capacity for dimer photoreactivation. However, we show that cell culture conditions can affect photoreactivating enzyme levels and thus, cellular dimer photoreactivation capacity. Cells grown in Eagle's minimal essential medium (supplemented with 15% fetal bovine serum) contain very low levels of photoreactivating enzyme and cannot photoreactivate dimers in their DNA; however, companion cultures maintained in Dulbecco's modified Eagle's minimal medium do contain photoreactivating enzyme and can photoreactivate cellular dimers.

Studies on the DNA photoreactivating enzyme from Escherichia coli: I. Transduction of the phr gene by bacteriophage lambda

Isolation and characterization of the photoreactivating enzyme, which repairs UV-irradiated DNA by using visible or near ultraviolet light to monomerize pyrimidine dimers, have been impeded principally by the low cellular content of the enzyme. We have greatly increased the photoreactivating enzyme activity in E. coli through use of a transducing phage carrying the phr gene. We constructed a transducing phage, λcI857S7dg D → J, and have shown that after induction of an E. coli strain lysogenic for this phage there is approximately 2000 times as much photoreactivating enzyme activity in cell free extracts as is found with the parental strain. These results, as well as those on the capacity for photoreactivation of colony-forming ability of strains with deletions of known extent, indicate that phr lies between gal and attλ.

Phylogenetic significances of the photoreactivable sectors of species of Hansenula.

Each species of the genus Hansenula has been tested for the extent to which cellular inactivation by ultraviolet radiation is mitigated by photoreactivation. The values obtained conform to a pattern consistent with the phylogenetic relationships between the species proposed by Wickerham. These findings corroborate previous indications that (i) fixation of the capacity for photoreactivation is an important element in the evolution of yeasts and that (ii) opportunity for environmental exposure of yeasts to solar ultraviolet radiation is not the determining factor in natural selection for their abilities to photo-reactivate.

Mechanism of photeractivation of pseudorabies virus.

Primary chick embryo cultures were able to photoreactivate ultraviolet-treated pseudorabies virus. Upon exposure to fluorescent light, infected or uninfected chick cells eliminated thymine dimers induced in their deoxyribonucleic acid by ultraviolet irradiation. In contrast, rabbit kidney cells did not photoreactivate the virus or eliminate thymine dimers. Thus, the capacity for photoreactivation appeared to be determined by the ability of the cell to eliminate thymine dimers.