ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03083.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract—Fluence rate and irradiance, two parameters used to quantify light and ultraviolet radiation, do not have a constant relation under natural light conditions. A method is described for measuring fluence rate, the preferred parameter, using meters intended for irradiance measurements. Values measured under natural light conditions are compared to a daylight mode

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03084.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract—Our major aim is to illustrate an approach for hindcasting or forecasting UV radiation (UVR, 280–400 nm) effects onin siturates of aquatic primary production when field measurements do not include estimates of UVR effects. A composite of spectral field measurements is employed to model UVR‐dependent rates of photosynthesis in diatomdominated waters in a coastal region of the Southern Ocean. Assumptions, caveats and limitations of the modeling are discussed. Calculations begin with the 1991 Palmer Long Term Ecological Research (LTER) primary production and optical databases, from which daily integrated rates of carbon fixation in the absence of UVR are calculated as a function of depth for a 140 km transect line sampled between dawn and dusk of a single day (14 November 1991). The UVR measurements from the nearby NSF/OPP Polar Network at Palmer Station are used to determine ozone (O3) concentration on the day of the transect, which is then employed in Madronich's (InUV‐B Radiation and Ozone Depletion(Edited by M. Tevini), pp. 17–68. Lewis, Boca Raton, FL, 1993) spectral code to model daytime variations in surface spectral irradiances under clear sky conditions. These data are corrected for cloudiness and then combined with estimates of in‐water UVR spectral attenuation coefficients, derived fromIcecolors 90data, to estimatein situlight exposure for phytoplankton collected at different depths and locations. An absolute chlorophyllspecific biological weighting function (BWF), determined under natural solar light fields for Antarctic diatom communities and shown to be reproducible while differing from a laboratory diatom BWF and otherin situBWF determined for other phytoplankton assemblages, is combined with estimates ofin situUVR exposure to derivein situestimates of chlorophyllspecific losses of carbon fixation due to UVR inhibittion. By repeating calculations for every sampling site along the transect, we derive a spatial map of estimated UVR effects on primary production across the region. We repeat calculations for different O, concentrations expected during the austral spring over Antarctica and illustrate the O, dependency of UVB (280–320 nm) inhibition effects in near surface waters. We estimate ambient UVR reduced carbon fixation rates up to 65% in surface waters, depending upon location, down to undetectable levels at 36 m. Reducing stratospheric O3concentrations by 50% further inhibits near surface primary production by 8% and integrated primary production by 5%. Primary production was forced to subsurface maxima across the entire transect line in the pr

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03085.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract—There has been much recent concern about the effects of increased UV radiation at certain locations on the earth's surface. There have been extensive studies of ultraviolet radiation effects on phytoplankton and primary production, yet the effects of UVB upon bacterioplankton have been largely overlooked. Bacteria play a central role in the cycling of nutrients and energy flow to higher trophic levels, serving as both mineralizers and secondary producers that are consumed by higher organisms. We have begun to investigate the induction of DNA photodamage by UVB in marine planktonic communities using a highly specific radioimmunoassay to measure cyclobutane pyrimidine dimers in samples collected from the northern Gulf of Mexico. DNA damage in the bacterioplankton size‐fraction (0.8 μm<120 μm) in 9 of 10 samples. Diel patterns of dimer accumulation and repair were observed in surface waters over a 48 h period in the bacterioplankton size fraction and in the larger eukaryotic plankton size fraction. Depth profiles of DNA damage in the bacterioplankton size fraction appear to be dependent on surface water mixing. Damage was greatest in surface waters, decreased with depth and could be detected to 10 m in calm seas. No net accumulation of damage was observed in moderate seas, even at the surface. Solar radiation was found to inhibit significantly both3H‐thymidine and14C‐leucine incorporation. Ultraviolet B was responsible for approximately half of the total inhibition of3H‐thymidine incorporation, UVA contributing the other half of the inhibition. The vast majority of14C‐leucine incorporation inhibition was due to UVB, suggesting that protein synthesis is less affected by UVA. The results demonstrate that direct measures of DNA damage can be made of indigenous planktonic communities and that bacterioplankton are highly susceptible to UVB damage and may serve as a more sensitive indicator of UVR stress than other

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03086.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract—Photoinhibition of photosynthesis was investigated in the Mediterranean green algaHalimeda tunameasuring pulse amplitude modulation (PAM) chlorophyll fluorescence and oxygen evolutionin situunder solar radiation. Exposure to solar radiation at the surface caused a drastic decline in the photosynthetic quantum yield accompanied by a decline in the photochemical quenching, while the nonphotochemical quenching dramatically increased. The algae recovered from these effects within a few hours indicating that these are mainly due to reversible photoinhibition and only to a smaller extent to nonreversible photodamage. Individuals harvested from deeper waters were more affected than those from shallower waters. Photoinhibition occurs in this alga even in its natural habitat when the sun is at high angles as shown by measuring the fluorescence parameters at hourly intervals during the course of the day. Photoinhibition was less pronounced when the short wavelength band was increasingly removed from solar radiation using cut‐off filters. After exposure of thalli to solar radiation at the water surface, oxygen production decreased drastically within 30 min; this inhibition was even more pronounced in algae harvested from deeper waters. Oxygen measurements at different depths showed optimal photosynthesis at a depth of 1 m. Also for photosynthetic oxygen production inhibited by high solar irradiance at least partial recovery could be observed within several hours. Despite the fact that UVB accounts for a very small fraction of solar radiation, it has a considerable effect on photosynthesis, whereas UVA seems to contribute only little to photoinhibition inH. t

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03087.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract—Three UV treatments (PAR; PAR + UVA; PAR + UVA + UVB) were performed by placing different UV‐ab‐sorbing Alters over communities developing on ceramic tiles in a natural marine habitat near Korinthos, Greece. The experiment was repeated at three depths (0.5 m, 1 m, 1.5 m) below the surface of the sea. Differences in community structure due to UV radiation exposure were more pronounced during the early stages of community development. After the first 3 weeks of growth, the productivity of the PAR + UVA + UVB treatment was significantly lower than the PAR + UVA but not than the PAR treatment. This difference did not persist thereafter. At 5 weeks of growth, the productivity at 0.5 m was significantly lower that at 1.0 m. No other significant differences were observed. The findings of the present study suggest that periphytic communities occurring at the upper layers of the euphotic zone may be capable of adjusting to changes in environmental stresses such as by increased solar UVB irrad

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03088.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract—Genetic hybrids ofXiphophorusfishes have been used for decades to study heritable melanoma formation. In these models, overexpression of pigmentation patterns from melanin‐producing pigment cells can lead to genetically regulated melanoma formation in backcross hybrids. In the best studied of these models, the Gordon‐Kosswig hybrid melanoma, tumors form spontaneously in all individuals of a subset of backcross hybrids between the platyflshXiphophorus maculatusJp 163 A and the swordtail speciesXiphophorus helleri.Backcross hybrids susceptible to melanoma formation inherit a sex‐linked oncogene,Xmrk, associated with the spotted dorsal (Sd) pigment pattern and have lost both copies of an autosomal gene,DIFF, from theX. maculatusparent. Spontaneous melanoma formation conforms to simple, two‐gene Mendelian inheritance in whichDIFFbehaves as a recessive tumor suppressor gene. Recently,Xiphophorushybrids in which melanomas can be induced by UV and near‐UV visible light exposure have been described. We report here results of genetic linkage analysis of one of theseXiphophoruslight‐inducible hybrid melanoma models, in backcross hybrids between the two platyflsh speciesX. maculatusJp 163 B andXiphophorus couchianus.Our linkage results provide the first estimate of recombination between the tumor suppressor locus,DIFF, and glycerate‐2‐dehydrogenase (GLYDH) inXiphophoruslinkage group V. Also, they demonstrate thatDIFFregulates hyperplasia of spotted side (Sp) pigment cells in this hybrid model, analogous to its regulation of hyperplasia ofSdpigment cells in the “classical” Gordon‐Kosswig hybrid. Joint segregation analyses of melanoma‐bearing fish indicate that segregation ofDIFFis genetically linked to melanoma induction by 405 nm light in this model but that induction of melanomas by UV wavelengths apparently does not depend on se

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03089.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract—Many amphibian species, in widely scattered locations, currently show population declines and/or reductions in range, but other amphibian species show no such declines. There is no known single cause for these declines. Differential sensitivity to UVB radiation among species might be one contributing factor. We have focused on amphibian eggs, potentially the most UVB‐sensitive stage, and compared their resistance to UVB components of sunlight with their levels of photolyase, typically the most important enzyme for repair of the major UV photoproducts in DNA, cyclobutane pyrimidine dimers. Photolyase varied 100‐fold among eggs/oocytes of 10 species. Among three species–Hyla regilla, Rana cascadae, andBufo boreas–for which resistance of eggs to solar UVB irradiance in their natural locations was measured, hatching success correlated strongly with photolyase. Two additional species,Rana auroraandAmbystoma gracile, now show similar correlations. Among the low‐egg‐photolyase species,R. cascadaeandB. boreasare showing declines, and the status ofA. gracileis not known. Of the two high‐photolyase species, populations ofH. regillaremain robust, but populations ofR. auroraare showing declines. To determine whether levels of photolyase or other repair activities are affected by solar exposures during amphibian development, we have initiated an extended study ofH. regillaandR. cascadae, and ofXenopus laevis, laboratory‐reared specimens of which previously showed very low photolyase levels.Hyla regillaandR. cascadaetadpoles are being reared to maturity in laboratories supplemented with modest levels of UV light or light filtered to remove UVB wavelengths. YoungX. laevisfemales are being reared indoors and outdoors. Initial observations reveal severe effects of both UVA and UVB light onH. regillaandR. cascadaetadpoles and metamorphs, including developmental abnormalities and high mortalities. Assays of photolyase levels in the skins of young animals roughly parallel previous egg/oocyte photolyase measurements for

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03090.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract—Different cultivars of maize (Zea maysL.) originating from Central and South Europe were grown from June to September 1994 for 16 weeks in two greenhouses covered with different UVB‐absorbing (280–320 nm) plastic foils. Using the ambient UVB radiation level of a southern location (Portugal, 38.7°N) in one of the greenhouses as an enhanced radiation compared to the reduced radiation in the second greenhouse, an increase of about 12% of UVB was simulated. Six of the eight cultivars examined showed significant reductions in height of up to 18.9% at all developmental stages under increased UVB. In contrast to this, the fresh and dry weight as well as the leaf area was reduced under UVB only at early developmental stages, but with ongoing development the UVB stressed plants caught up. The total content of absorbing compounds of the maize cultivars was completely unaffected by UVB. A flowering delay up to a maximum of 5 days was observed under higher UVB in several cultivars. Probably due to this delay in the cob development the yield decreased to 27.7% under higher UVB at the first harvest after 12 and 14 weeks, whereas at the second harvest after 14 and 16 weeks yield reduction levell

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03091.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract—We have determined the capacity of soybean seedlings to repair DNA damage by UV doses that do not produce apparent injury in the plants. They remove cyclobutane pyrimidine dimers by both excision and photoreactiva‐tion. The rates and relative contributions of these repair processes were determined as a function of initial level of cyclobutyl pyrimidine dimers. Photoreactivation was detected in seedlings at all initial dimer levels. Although excision was not observed at the lowest dimer frequencies, at higher initial dimer levels it was quite effective in dimer removal. The rates of repair in soybean were substantially higher than in alfalfa seedlings at the same DNA damage lev

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03092.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY