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Because of their sessile life style, plants have evolved the ability to adjust to environmentally harsh conditions. An important aspect of stress adaptation involves the reprogramming of the cell cycle to ensure optimal growth. The atypical E2F transcription factor DP-E2F-like 1 (E2Fe/DEL1) had been found previously to be an important regulator of the endocycle onset. Here, a novel role for E2Fe/DEL1 was identified as a transcriptional repressor of the type-II cyclobutane pyrimidine dimer-photolyase DNA repair gene PHR1. Upon ultraviolet-B (UV-B) treatment, plants knocked out for E2Fe/DEL1 had improved DNA repair abilities when compared with control plants, whereas those overexpressing it performed less well. Better DNA repair allowed E2Fe/DEL1 knockout plants to resume endoreduplication faster than control plants, contributing in this manner to UV-B radiation resistance by compensating the stress-induced reduction in cell number by ploidy-dependent cell growth. As E2Fe/DEL1 levels decreased upon UV-B treatment, we hypothesize that the coordinated transcriptional induction of PHR1 with the endoreduplication onset contributes to the adaptation of plants exposed to UV-B stress.

Plants respond to low levels of UV-B radiation with a coordinated photomorphogenic response that allows acclimation to this environmental stress factor. The key players in this UV-B response are COP1 (an E3 ubiquitin ligase), UVR8 (a β-propeller protein), and HY5 (a bZIP transcription factor). We have shown previously that an elevated UV-B-specific response is associated with dwarf growth, indicating the importance of balancing UV-B-specific signaling. Negative regulators of this pathway are not known, however. Here, we describe two highly related WD40-repeat proteins, REPRESSOR OF UV-B PHOTOMORPHOGENESIS 1 (RUP1) and RUP2, that interact directly with UVR8 as potent repressors of UV-B signaling. Both genes were transcriptionally activated by UV-B in a COP1-, UVR8-, and HY5-dependent manner. rup1 rup2 double mutants showed an enhanced response to UV-B and elevated UV-B tolerance after acclimation. Overexpression of RUP2 resulted in reduced UV-B-induced photomorphogenesis and impaired acclimation, leading to hypersensitivity to UV-B stress. These results are consistent with an important regulatory role for RUP1 and RUP2, which act downstream of UVR8-COP1 in a negative feedback loop impinging on UVR8 function, balancing UV-B defense measures and plant growth.

Long-term effects of ultraviolet (UV) radiation on flavonoid biosynthesis were investigated in Arabidopsis thaliana using the sun simulators of the Helmholtz Zentrum München. The plants, which are widely used as a model system, were grown (1) at high photosynthetically active radiation (PAR; 1,310 micromol m(-2) s(-1)) and high biologically effective UV irradiation (UV-B(BE) 180 mW m(-2)) during a whole vegetative growth period. Under this irradiation regime, the levels of quercetin products were distinctively elevated with increasing UV-B irradiance. (2) Cultivation at high PAR (1,270 micromol m(-2) s(-1)) and low UV-B (UV-B(BE) 25 mW m(-2)) resulted in somewhat lower levels of quercetin products compared to the high-UV-B(BE) conditions, and only a slight increase with increasing UV-B irradiance was observed. On the other hand, when the plants were grown (3) at low PAR (540 micromol m(-2) s(-1)) and high UV-B (UV-B(BE) 180 mW m(-2)), the accumulation of quercetin products strongly increased from very low levels with increasing amounts of UV-B but the accumulation of kaempferol derivatives and sinapoyl glucose was less pronounced. We conclude (4) that the accumulation of quercetin products triggered by PAR leads to a basic UV protection that is further increased by UV-B radiation. Based on our data, (5) a combined effect of PAR and different spectral sections of UV radiation is satisfactorily described by a biological weighting function, which again emphasizes the additional role of UV-A (315-400 nm) in UV action on A. thaliana.

Plants in alpine habitats are exposed to many environmental stresses, in particular temperature and radiation extremes. Recent field experiments on Arnica montana L. cv. ARBO indicated pronounced altitudinal variation in plant phenolics. Ortho-diphenolics increased with altitude compared to other phenolic compounds, resulting in an increase in antioxidative capacity of the tissues involved. Factors causing these variations were investigated by climate chamber (CC) experiments focusing on temperature and ultraviolet (UV)-B radiation. Plants of A. montana L. cv. ARBO were grown in CCs under realistic climatic and radiation regimes. Key factors temperature and UV-B radiation were altered between different groups of plants. Subsequently, flowering heads were analyzed by HPLC for their contents of flavonoids and caffeic acid derivatives. Surprisingly, increased UV-B radiation did not trigger any change in phenolic metabolites in Arnica. In contrast, a pronounced increase in the ratio of B-ring ortho-diphenolic (quercetin) compared to B-ring monophenolic (kaempferol) flavonols resulted from a decrease in temperature by 5 degrees C in the applied climate regime. In conclusion, enhanced UV-B radiation is probably not the key factor triggering shifts in the phenolic composition in Arnica grown at higher altitudes but rather temperature, which decreases with altitude.

The impact of UV-B radiation on 10 genotypically different barley and tomato cultivars was tested in a predictive study to screen for potentially UV-tolerant accessions and to analyze underlying mechanisms for UV-B sensitivity. Plant response was analyzed by measuring thermoluminescence, fluorescence, gas exchange and antioxidant status. Generally, barley cultivars proved to be much more sensitive against UV-B radiation than tomato cultivars. Statistical cluster analysis could resolve two barley groups with distinct differences in reaction patterns. The UV-B sensitive group showed a stronger loss in PSII photochemistry and a lower gas-exchange performance and regulation after UV-B radiation compared to the more tolerant group. The results indicate that photosynthetic light and dark reactions have to play optimally in concert to render plants more tolerant against UV-B radiation. Hence, measuring thermoluminescence/fluorescence and gas exchange in parallel will have much higher potential in identifying tolerant cultivars and will help to understand the underlying mechanisms.

The ultraviolet-B (UV-B) portion of the solar radiation functions as an environmental signal for which plants have evolved specific and sensitive UV-B perception systems. The UV-B-specific UV RESPONSE LOCUS 8 (UVR8) and the multifunctional E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) are key regulators of the UV-B response. We show here that uvr8-null mutants are deficient in UV-B-induced photomorphogenesis and hypersensitive to UV-B stress, whereas overexpression of UVR8 results in enhanced UV-B photomorphogenesis, acclimation and tolerance to UV-B stress. By using sun simulators, we provide evidence at the physiological level that UV-B acclimation mediated by the UV-B-specific photoregulatory pathway is indeed required for survival in sunlight. At the molecular level, we demonstrate that the wild type but not the mutant UVR8 and COP1 proteins directly interact in a UV-B-dependent, rapid manner in planta. These data collectively suggest that UV-B-specific interaction of COP1 and UVR8 in the nucleus is a very early step in signalling and responsible for the plant's coordinated response to UV-B ensuring UV-B acclimation and protection in the natural environment.

There is limited information on the impact of present-day ultraviolet-B (UV-B) radiation on a reprogramming of gene expression in crops. Summer wheat was cultivated in controlled environmental facilities under simulated realistic climatic conditions. We investigated the effect of different regimes of UV-B radiation on summer wheat (Triticum aestivum L.) cultivars Nandu, Star and Turbo. Until recently, these were most important in Bavaria. Different cultivars of crops often show great differences in their sensitivity towards UV-B radiation. To identify genes that might be involved in UV-B defence mechanisms, we first analyzed selected genes known to be involved in plant defence mechanisms. RNA gel blot analysis of RNA isolated from the flag leaf of 84-day-old plants showed differences in transcript levels among the cultivars. Flag leaves are known to be important for grain development, which was completed at 84 days post-anthesis. Catalase 2 (Cat2) transcripts were elevated by increased UV irradiation in all cultivars with highest levels in cv. Nandu. Pathogenesis-related protein 1 (PR1) transcripts were elevated only in cv. Star. A minor influence on transcripts for phenylalanine ammonia-lyase (PAL) was observed in all three cultivars. This indicates different levels of acclimation to UV-B radiation in the wheat cultivars studied. To analyze these responses in more detail, UV-B-exposed flag leaves of 84-day-old wheat (cv. Nandu) were pooled to isolate cDNAs of induced genes by suppression-subtractive hybridization (SSH). Among the initially isolated cDNA clones, 13 were verified by RNA gel blot analysis showing an up-regulation at elevated levels of UV-B radiation. Functional classification revealed genes encoding proteins associated with protein assembly, chaperonins, programmed cell death and signal transduction. We also studied growth, flowering time, ear development and yield as more typical agricultural parameters. Plant growth of young plants was reduced at increased UV-B radiation. Flowering and ear development were delayed concomitantly, whereas total grain weight was not influenced at any of the UV-B irradiation regimes.

The major UV-B screening pigments of the epidermal layer of Scots pine (Pinus sylvestris) needles are flavonol 3-o-glycosides (F3Gs) esterified with hydroxycinnamic acids at positions 3" and 6". Acylation is the last step in biosynthesis and is catalysed by position-specific hydroxycinnamoyl transferases (3" and 6"HCT). The UV-B dependence of these enzyme activities was studied in primary needles of Scots pine seedlings grown under different UV-B conditions in environmentally controlled sun simulators. 6"HCT activity was induced upon UV-B irradiation while 3"HCT activity was not induced but showed high constitutive values. To investigate the biosynthesis of diacylated F3Gs during needle development under natural conditions, the HCT activities and metabolite contents were analysed in needles of field-grown mature pine trees. Accumulation of diacylated compounds as well as of 6"HCT activity occurred transiently in the first year of needle development only. In contrast, 3"HCT activity exhibited broad maxima in two consecutive years during needle growth. The data suggest that acylated F3Gs are first formed as soluble compounds which are then translocated into the cell wall to be bound by their hydroxycinnamoyl residues.

Polyamines have been described to protect against numerous oxidative stresses in plants. Increasing UV-B radiation (280-315 nm) in the biosphere may also induce an increase in radical formation in tissues. This study employed the tobacco cultivars Bel B and Bel W3 to describe possible protective functions of polyamines against UV-B radiation in sun light simulators (GSF/Munich) with natural diurnal fluctuations of simulated UV-B. Polyamine measurements on a whole leaf basis in isolated chloroplasts and thylakoids were paralleled to photosynthetic and respiration rates, photosynthetic efficiency, leaf thickness and photosynthetic pigment compositions. The study revealed that an increase of polyamines, and especially of putrescine level in thylakoid membranes upon elevated UV-B exposure comprises one of the primary protective mechanisms in the photosynthetic apparatus of the tobacco variety Bel B against UV-B radiation. The tobacco cultivar Bel W3, sensitive to ozone, was also proved to be sensitive to UV-B. This sensitivity is attributed to its incapability to enhance putrescine level in thylakoid membranes. After prolongation of UV-B exposure, when endogenous plant balances are being gradually restored, due to secondary responses, (e.g., biosynthesis of carotenoids and of additional flavonoids) and the plant is adapting to the altered environmental conditions, then the polyamine level is being reduced. Thus, we can discriminate the UV-B induced stress period from a UV-B acclimation period.

In plants, hydrogen peroxide (H(2)O(2)) plays a major signaling role in triggering both a defense response and cell death. Increased cellular H(2)O(2) levels and subsequent redox imbalances are managed at the production and scavenging levels. Because catalases are the major H(2)O(2) scavengers that remove the bulk of cellular H(2)O(2), altering their levels allows in planta modulation of H(2)O(2) concentrations. Reduced peroxisomal catalase activity increased sensitivity toward both ozone and photorespiratory H(2)O(2)-induced cell death in transgenic catalase-deficient Arabidopsis thaliana. These plants were used as a model system to build a comprehensive inventory of transcriptomic variations, which were triggered by photorespiratory H(2)O(2) induced by high-light (HL) irradiance. In addition to an H(2)O(2)-dependent and -independent type of transcriptional response during light stress, microarray analysis on both control and transgenic catalase-deficient plants, exposed to 0, 3, 8, and 23 h of HL, revealed several specific regulatory patterns of gene expression. Thus, photorespiratory H(2)O(2) has a direct impact on transcriptional programs in plants.

Photodegradation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polycyclic aromatic hydrocarbons (PAHs) sorbed on surfaces of spruce (Picea abies (L.) Karst.) needles was investigated. The role of sunlight and, in particular, the role of short wavelength UV-B radiation were studied in a sun simulator under controlled environmental conditions. The photodegradation of PCDD/Fs and PAHs follows first-order kinetics. Simulated sunlight containing UV-B induced two phases of photodegradation kinetics for PCDD/Fs, whereas no distinct phases of the kinetics were observed for PAHs. UV-B radiation plays a much more important role on the photodegradation for PCDD/Fs than that for PAHs. Direct photolysis dominates the photodegradation of PCDD/Fs and PAHs.

Plant secondary metabolism significantly contributes to defensive measures against adverse abiotic and biotic cues. To investigate stress-induced, transcriptional alterations of underlying effector gene families, which encode enzymes acting consecutively in secondary metabolism and defense reactions, a DNA array (MetArray) harboring gene-specific probes was established. It comprised complete sets of genes encoding 109 secondary product glycosyltransferases and 63 glutathione-utilizing enzymes along with 62 cytochrome P450 monooxygenases and 26 ABC transporters. Their transcriptome was monitored in different organs of unstressed plants and in shoots in response to herbicides, UV-B radiation, endogenous stress hormones, and pathogen infection. A principal component analysis based on the transcription of these effector gene families defined distinct responses and crosstalk. Methyl jasmonate and ethylene treatments were separated from a group combining reactions towards two sulfonylurea herbicides, salicylate and an avirulent strain of Pseudomonas syringae pv. tomato . The responses to the herbicide bromoxynil and UV-B radiation were distinct from both groups. In addition, these analyses pinpointed individual effector genes indicating their role in these stress responses. A small group of genes was diagnostic in differentiating the response to two herbicide classes used. Interestingly, a subset of genes induced by P. syringae was not responsive to the applied stress hormones. Small groups of comprehensively induced effector genes indicate common defense strategies. Furthermore, homologous members within branches of these effector gene families displayed differential expression patterns either in both organs or during stress responses arguing for their non-redundant functions.

Polysulphone film is used as a personal UV dosemeter in dermatological or epidemiological studies. The relative efficiency of this detector does not exactly match the action spectrum as proposed by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and to which the UV dose and exposure limits refer. Therefore, the calibration of the dosemeter depends on the spetrum. In the present paper the variation of the calibration factor for terrestrial solar UV spectra is analysed on the basis of a two year observation period at a site near Munich. Germany. A detailed error estimation is included. It is shown that the variation of the calibration factor within this class of spectra is the main contribution to the total uncertainty of the dose determination, which can be up to 40%. The shape of the spectrum of terrestrial solar UV radiation is mainly determined by the total ozone column and the solar elevation angle. It is shown how the calibration depends on these two parameters and how this additional information can help to reduce the measurement error to a residual uncertainty of 17%. Exposure studies of terrestrial solar UV radiation using polysulphone film as a dosemeter would gain in accuracy if total ozone column values at the study's site could be measured or taken from satellite or weather service data. The interpretation of the magnitude of the dose uncertainty depends on the further use of these data.

Long-term depletion of the stratospheric ozone layer contributes to an increase in terrestrial solar ultraviolet-B radiation. This has deleterious effects on living organisms, such as DNA damage. When exposed to elevated ultraviolet-B radiation (UV-B; 280-315 nm), plants display a wide variety of physiological and morphological responses characterized as acclimation and adaptation. Here we show, using special sun simulators, that elevated solar UV-B doses increase the frequency of somatic homologous DNA rearrangements in Arabidopsis and tobacco plants. Increases in recombination are accompanied by a strong induction of photolyase and Rad51 gene expression. These genes are putatively involved in major DNA repair pathways, photoreactivation and recombination repair. In mutant Arabidopsis plants that are deficient in photoreactivating ultraviolet-induced cyclobutane pyrimidine dimers, recombination under elevated UV-B regimes greatly exceeds wild-type levels. Our results show that homologous recombination repair pathways might be involved in eliminating UV-B-induced DNA lesions in plants. Thus, increases in terrestrial solar UV-B radiation as forecasted for the early 21st century may affect genome stability in plants.

The role clouds play in the modification of global radiation is still a major uncertainty in the risk assessment of UV effects on ecological systems and human health. This study presents cloud transmission data obtained from measurements with Robertson-Berger meters and simultaneous cloud observations. The global transmission of erythemally weighted irradiance depends strongly on cloud amount and can be described by a cubic function. The comparison with results derived from long-term records of total global irradiance indicates no statistically significant difference between the attenuation of erythemal and total global radiation. The large variance of data results from lumping together data from different cloud types. Classification of data according to cloud forms yields a more satisfactory fit. The coefficient of the cubic term characterizes the ability of various cloud forms to attenuate UV radiation. It varies between 0.4 for high clouds and approximately 1.0 for cumulonimbus. This attenuation parameter allows a quantitative description of the cloud influence on irradiance and therefore a more accurate risk assessment.

The degradation of sensitizers used in photodynamic therapy (PDT) involves photooxidation either by molecular oxygen or by oxygen intermediates which leads to hydroxyaldehyde and formyl products or to ring opening. Our investigations focused on the spectroscopic changes which protoporphyrin-dimethylester (PP) exhibits upon irradiation. As the microenvironment strongly influences the effects, we used an aprotic organic solvent, L-alpha-phosphatidylcholine dioleoyl (DOPC) liposomes and isogenic fibrosarcoma cells (SSKII) as carriers for PP. Hydroxyaldehyde product isomers develop a new absorption band centred around 670 nm and a new emission band at 676 nm. These characteristics can be used to discriminate them from formyl products and intact PP. In organic solvents, the formation of the hydroxyaldehyde products dominates. In DOPC liposomes and cells, the hydroxyaldehyde yield drops and photooxidation results in attack of the macrocycle. Time-resolved fluorescence spectroscopy of monomeric PP in an organic solvent gives a monoexponential decay time tau of 10.1 +/- 1.3 ns. Upon irradiation a second component with a decay time of 4.9 +/- 0.6 ns, resulting from the hydroxyaldehyde product, was detected. In liposomes and cells the monomeric decay time was significantly longer (15 ns) due to the altered microenvironment. Additionally, we observed in liposomes and in cells a small contribution of a short component (1 ns) which is attributed to an aggregated sensitizer species. In irradiated cells the aggregated fraction doubles, indicating a change in the microenvironment caused by the photodynamic action of the sensitizer.

We studied the optical and color performance of Olympus fiber- and electronic endoscopes, including the EVIS 100 and EVIS 200 series. The measurements showed that the optical resolution of new generation videoendoscopes equals or exceeds that of fiberendoscopes. The close-up focusing ability has been extended. The color performance of the new EVIS 200 gastroscope enables clear distinction of all mucosal hues.

The effects of solvent pH on spectral properties and fluorescence decay kinetics were investigated in order to characterize the microenvironment of meso-tetraphenylporphine tetrasulphonate (TPPS4) taken up by cells. Steady-state absorption and fluorescence spectra of TPPS4 in buffer solutions of different pH were used to identify a ring protonated species at pH less than or equal to 4. This dictation could also be distinguished from the unprotonated form by its altered fluorescence decay time (3.5 vs. 11.4 ns). In addition, time-resolved spectroscopy gave some evidence of a monocationic species existing at pH 6-9. This was concluded from the occurrence of another component with a decay time of 5 ns. Measurements of the spectral and kinetic properties of the fluorescence emission of single epithelial cells (RR1022) incubated with TPPS4 indicated that the sensitizer was mainly localized in a microenvironment with a pH of 5, a value which occurs intracellularly only within lysosomes. Cells kept in the dark exhibited the characteristic spectra of both the dication and the neutral form. The fluorescence decay showed two components with decay times of 2.6 ns and 10.6 ns. Irradiation of the cells changed the decay times to 4.6 ns and 13.4 ns and the dication fluorescence emission peak vanished, which is in accordance with the results obtained from buffer solutions at pH greater than or equal to 6. Therefore, we deduce that the photodynamic action leads to a rupture of the lysosomes and that the sensitizer is released into the surrounding cytoplasm.

Porphyrin monomers, dimers and aggregates, which can be differentiated on the basis of their fluorescence lifetimes, are shown to possess different degrees of fluorescence polarization. This opens up new possibilities for microscopic imaging of these individual components in photosensitization and tumour detection. A rough estimate of the size of the porphyrin aggregates is obtained from the data of time-resolved fluorescence anisotropy.

At present, video endoscopic systems (VE) are available from four companies. We have had an opportunity to test these instruments in clinical practice. In principle, all the VE's are similar in that they employ charge coupling devices (CCD-chips) as image sensors, but they differ significantly in CCD chip technology and in the color acquisition technique. The basic aspects of CCD chip and transmission technology of relevance to the endoscopist are discussed. The mechanical properties of the endoscopes are listed. Finally, we provide an outlook on the determinants of the optical performance of VE's. The optical performance of a VE can be characterized by its resolution and color performance.

The subject of this study was the optical performance of video-endoscopic systems (VE) in terms of maximal resolving power and resolvable picture elements. Olympus, Toshiba/Machida, Fujinon, and Welch Allyn video gastroscopes were tested. A GIF Q 10 fiberscope from Olympus was also included for comparison. The resolution measurements were made at various distances using two independent methods--electronic analysis of the TV signal, and visual evaluation of the resolution, of a standardized test target. The results obtained with the two methods were in perfect agreement. The resolution of fine details clearly depends on the distance between the distal end and the target because of decreasing image scale. Depending on the individual optical design, the various VE's show maxima at different distances. At shorter distances, the image is degraded by defocusing. An optimal distance which is as small as possible is desired for clinical routine. Apart from the fiberscope this requirement is best met by the Fuji system. The greatest resolution is obtained with the Toshiba system but at the cost of the viewing angle which is the smallest of all the systems. Fuji combines relatively high resolution with a large viewing angle. Because of the widely varying viewing angle a comparison based solely on resolution cannot represent the true imaging capability of the system. We therefore eliminated purely optical parameters and calculated the number of resolvable picture elements per line. We regard this number to be a fair characterization of both TV and fiber systems.

The article focuses on techniques and applications of time-resolved fluorescence spectroscopy in biology and medicine. Both novel methods and well-established ones are discussed and future trends are outlined. Applications including fluorescence detection of nucleic acids, proteins, coenzymes and plant pigments and fluorescence labelling of nuclei, membranes and antibodies are outlined. In addition the fluorescence properties of photosensitizers used in photodynamic therapy are discussed.

We have conducted a study aimed at testing the color performance of video endoscopes in quantitative terms for the first time. The video endoscopes investigated were from Fuji, Olympus, Toshiba/Machida, and Welch-Allyn. The tests were carried out with an opto-electronic color analyser using standardized color charts and a neutral grey chart. Hue and chroma of the reproduced colors were measured. The Olympus video endoscope reproduces the hue very well, showing only slight color desaturation. The Fuji video endoscope had a yellowish tint, whereas the picture obtained with the WA video endoscope produced an inhomogeneous picture with a pronounced red/purplish cast at the top of the screen and almost neutral reproduction at the lower half. The Toshiba video endoscope was the only one with a color chip, and reproduced hue fairly well, but its colors were weakly saturated.