Peter Boelen

DEPTH DISTRIBUTIONS OF DNA DAMAGE IN ANTARCTIC MARINE PHYTO‐ AND BACTERIOPLANKTON EXPOSED TO SUMMERTIME UV RADIATION

During a survey from January to March 1998, the occurrence of UV‐B radiation (UVBR)‐ induced DNA damage in Antarctic marine phytoplankton and bacterioplankton was investigated. Sampling was done in Ryder Bay, off the British base Rothera Station, 67°S, 68°W (British Antarctic Survey). Samples were taken regularly during the survey period at fixed depths, after which DNA damage was measured in various plankton size fractions (>10, 2–10, and 0.2–2 μm). Incident solar radiation was measured using spectroradiometry, whereas attenuation of biologically effective UVBR was studied using a DNA dosimeter. A diatom bloom was found in the bay during the research period, judging from microscopic observations and HPLC analyses of taxon‐specific pigments. The high phytoplankton biomass likely caused strong attenuation of DNA effective UVBR (Kbd‐eff). Kbd‐eff values ranged from 0.83·m−1 at the peak of the bloom to 0.47·m−1 at the end of the season. UVBR‐mediated DNA damage, as measured by cyclobutane pyrimidine dimer (CPD) abundance, was detected in all plankton size fractions. Highest levels were found in the smallest size fraction, mainly consisting of heterotrophic bacteria. Clear CPD depth profiles were found during mid‐summer (January, beginning of February) with surface levels exceeding 100 CPDs per million nucleotides in the bacterioplankton fraction. At that time, melting of the continuously present shelf ice caused strong salinity gradients in the upper meters, thereby stimulating water column stabilization. At the end of February and beginning of March, this phenomenon was less pronounced or absent. At that time, DNA damage was homogeneously distributed over the first 10 m, ranging between 20 and 30 CPDs per million nucleotides for the smallest size fraction.

Effects of temperature on the photoreactivation of ultraviolet-B-induced DNA damage in Palmaria palmata (Rhodophyta)

The accumulation of DNA damage (thymine dimers and 6‐4 photoproducts) induced by ultraviolet‐B radiation was studied in Palmaria palmata (L.) O. Kuntze under different light and temperature conditions, using specific monoclonal antibodies and subsequent chemiluminescent detection. Both types of damage were repaired much faster under ultraviolet‐A radiation (UVAR) plus photosynthetically active radiation (PAR) than in darkness, which indicates photoreactivating activity. At 12° C, all thymine dimers were repaired after 2 h irradiation with UVAR plus PAR, whereas 6‐4 photoproducts were almost completely repaired after 4 h. After 19 h of darkness, almost complete repair of 6‐4 photoproducts was found, and 67% of the thymine dimers were repaired. In a second set of experiments, repair of DNA damage under UVAR plus PAR was compared at three different temperatures (0, 12, and 25° C). Again, thymine dimers were repaired faster than 6‐4 photoproducts at all three temperatures. At 0° C, significant repair of thymine dimers was found but not of 6‐4 photoproducts. Significant repair of both thymine dimers and 6‐4 photoproducts occurred at 12 and 25° C. Optimal repair efficiency was found at 25° C for thymine dimers but at 12° C for 6‐4 photoproducts, which suggests that the two photorepair processes have different temperature characteristics.

Attenuation of biologically effective UV radiation in tropical atlantic waters measured with a biochemical DNA dosimeter

Abstract— A biochemical dosimeter was developed to study the attenuation of biologically effective UV radiation in marine tropical waters. Small quartz vials were used containing a solution of DNA molecules; the vials were incubated at discrete water depths. Subsequently, DNA damage was determined in these samples, using an antibody directed against thymine dimers followed by chemiluminescent detection. Measurements of DNA damage were compared with calculated biologically effective doses, as derived from spectroradiometer measurements. The biodosimeter was found to be a reliable and easy tool to determine levels of harmful UV radiation in marine waters. The highest attenuation coefficient (1.60 m‐l) measured with the biochemical dosimeter was found in eutrophic waters, at a coastal station off Curabcao, Netherlands Antilles. At the other stations attenuation coefficients ranged from 0.18 m‐1 in central Atlantic waters to 0.43 m‐1 close to the Curapcao coast line. Latter results indicate that biologically effective UV radiation may easily reach ecologically significant depths, e.g. coral reef communities.

Diel Patterns of UVBR-Induced DNA Damage in Picoplankton Size Fractions from the Gulf of Aqaba, Red Sea

This study focuses on the impact of natural levels of UVBR (ultraviolet-B radiation: 280 to 315 nm) on bacterio- and phytoplankton (<10 mm) from the Gulf of Aqaba, Red Sea. Incident biologically effective doses (BEDs) and attenuation of biologically effective radiation in the water column were measured using a DNA biodosimeter. UVBR-induced DNA damage was measured as cyclobutane pyrimidine dimers (CPDs), using an antibody directed to CPDs followed by chemiluminescent detection. Depth profiles of DNA damage were determined in two plankton size fractions (0.2 to 0.8 mm and 0.8 to 10 mm) collected down to 50 m depth. Furthermore, accumulation and removal of CPDs were monitored in surface plankton samples during several daily cycles. Small plankton (plankton <10 mm) composition was determined by flow cytometry. The plankton community in the Gulf of Aqaba was dominated by nonphototrophic bacteria and the free-living prochlorophyte Prochlorococcus spp. (<0.8 mm). In general, no DNA damage could be detected in dosimeter DNA below 15 m. In contrast, DNA damage (up to 124 CPD Mnucl-1) could be detected in all bacterio- and phytoplankton samples. DNA damage accumulated throughout the day, indicating that plankton in the Gulf of Aqaba undergo UVBR stress via CPD induction. Although the numbers of CPDs decreased during darkness, both size fractions showed some residual DNA damage at the end of the night. This suggests that dark repair processes did not remove all CPDs, or that part of the plankton community was incapable of repair at all. CPD levels in the two size fractions showed no significant differences in situ. During full solar radiation exposures (samples incubated in bags), more CPDs were detected in the smaller (0.2 to 0.8 mm) size fraction as compared to the larger (0.8 to 10 mm) size fraction. In these experiments, initial plankton composition was significantly different from the field samples. This implies that a shift in the population structure or irradiance conditions can lead to a significant change in UVBR sensitivity. In conclusion, the results show that the picoplankton-dominated phyto- and bacterioplankton communities in the clear surface waters from the Gulf of Aqaba undergo UVBR stress. Repair pathways are not sufficient to eliminate damage during or after UVBR exposure hours, suggesting photomortality as a potential loss parameter of the plankton community.

Stratospheric ozone depletion: High arctic tundra plant growth on Svalbard is not affected by enhanced UV-B after 7 years of UV-B supplementation in the field

The response of tundra plants to enhanced UV-B radiation simulating 15 and 30% ozone depletion was studied at two high arctic sites (Isdammen and Adventdalen, 78° N, Svalbard).The set-up of the UV-B supplementation systems is described, consisting of large and small UV lamp arrays, installed in 1996 and 2002. After 7 years of exposure to enhanced UV-B radiation, plant cover, density, morphological (leaf fresh and dry weight, leaf thickness, leaf area, reproductive and ecophysiological parameters leaf UV-B absorbance, leaf phenolic content, leaf water content) were not affected by enhanced UV-B radiation. DNA damage in the leaves was not increased with enhanced UV-B in Salix polaris and Cassiope tetragona. DNA damage in Salix polaris leaves was higher than in leaves of C. tetragona. The length of male gametophyte moss plants of Polytrichum hyperboreum was reduced with elevated UV-B as well as the number of Pedicularis hirsuta plants per plot, but the inflorescence length of Bistorta vivipara was not significantly affected. We discuss the possible causes of tolerance of tundra plants to UV-B (absence of response to enhanced UV-B) in terms of methodology (supplementation versus exclusion), ecophysiological adaptations to UV-B and the biogeographical history of polar plants

The occurrence of p-coumaric acid and ferulic acid in fossil plant materials and their use as UV-proxy.

The applicability of p-coumaric acid and ferulic acid concentrations or ratios in (sub)fossil plant remnant as UV-B proxies relies on various aspects, which are discussed in this paper and will be illustrated with some experimental data. A newly developed THM-micropyrolysis–gas chromatography–mass spectrometry method was tested on various spores, pollen and other plant remains, which were analysed for the presence of the UV-absorbing compounds p-coumaric acid and ferulic acid. This revealed that these supposed building-blocks of sporopollenin appear to be present in pollen of many plant species but also in moss spores. The development of this micropyrolysis method paved the way for the quantitative analysis of UV-absorbing compounds in case only a small amount of analyte is available, for example for fossil pollen and spores but also other small palynomorphs and plant fossils. The use of this technique will provide a better insight in the plant responses to UV-radiation, the chemistry of pollen and spores, their fossil counterparts and furthermore the means for a further development of a proxy for the reconstruction of past UV-B radiation.

Outdoor studies on the effects of solar UV-B on bryophytes : Overview and methodology

In this review all recent field studies on the effects of UV-B radiation on bryophytes are discussed. In most of the studies fluorescent UV-B tubes are used to expose the vegetation to enhanced levels of UV-B radiation to simulate stratospheric ozone depletion. Other studies use screens to filter the UV-B part of the solar spectrum, thereby comparing ambient levels of UV-B with reduced UV-B levels, or analyse effects of natural variations in UV-B arising from stratospheric ozone depletion. Nearly all studies show that mosses are well adapted to ambient levels of UV-B radiation since UV-B hardly affects growth parameters. In contrast with outdoor studies on higher plants, soluble UV-B absorbing compounds in bryophytes are typically not induced by enhanced levels of UV-B radiation. A few studies have demonstrated that UV-B radiation can influence plant morphology, photosynthetic capacity, photosynthetic pigments or levels of DNA damage. However, there is only a limited number of outdoor studies presented in the literature. More additional, especially long-term, experiments are needed to provide better data for statistical meta-analyses. A mini UV-B supplementation system is described, especially designed to study effects of UV-B radiation at remote field locations under harsh conditions, and which is therefore suited to perform long-term studies in the Arctic or Antarctic. The first results are presented from a long-term UV-B supplementation experiment at Signy Island in the Maritime Antarctic.

On the potential application of polar and temperate marine microalgae for EPA and DHA production

Long chain polyunsaturated fatty acids (LC-PUFAs) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are considered essential omega-3 fatty acids in human nutrition. In marine microalgae EPA and/or DHA are allegedly involved in the regulation of membrane fluidity and thylakoid membrane functioning. The cellular content of EPA and DHA may therefore be enhanced at low temperature and irradiance conditions. As a result, polar and cold temperate marine microalgal species might potentially be suitable candidates for commercial EPA and DHA production, given their adaptation to low temperature and irradiance habitats.In the present study we investigated inter- and intraspecific EPA and DHA variability in five polar and (cold) temperate microalgae. Intraspecific EPA and DHA content did not vary significantly in an Antarctic (Chaetoceros brevis) and a temperate (Thalassiosira weissflogii) centric diatom after acclimation to a range of irradiance levels at two temperatures. Interspecific variability was investigated for two Antarctic (Chaetoceros brevis and Pyramimonas sp. (Prasinophyceae)) and three cold-temperate species (Thalassiosira weissflogii, Emiliania huxleyi (Prymnesiophyceae) and Fibrocapsa japonica (Raphidophyceae)) during exponential growth. Interspecific variability was shown to be much more important than intraspecific variability. Highest relative and absolute levels of DHA were measured in the prymnesiophyte E. huxleyi and the prasinophyte Pyramimonas sp., while levels of EPA were high in the raphidophyte F. japonica and the diatoms C. brevis and T. weissflogii. Yet, no significant differences in LC-PUFA content were found between polar and cold-temperate species. Also, EPA and DHA production rates varied strongly between species. Highest EPA production rate (174 μg L-1 day-1) was found in the Antarctic diatom Chaetoceros brevis, while DHA production was highest in the cold-temperate prymnesiophyte Emiliania huxleyi (164 μg L-1 day-1). We show that, following careful species selection, effective mass cultivation of marine microalgae for EPA and DHA production may be possible under low temperature and irradiance conditions.

A vegetation, climate and environment reconstruction based on palynological analyses of high arctic tundra peat cores (5000–6000 years BP) from Svalbard

As a reference for ongoing studies reconstructing past vegetation, climate and environment, pollen spectra in tundra peat profiles from Svalbard, were investigated. The base of tundra peat cores collected from Ny Alesund, Stuphallet, Blomstrand and Isdammen has been 14C dated to 350–490 BP, 5710 BP, 4670 BP and 700–900 BP, respectively. The Stuphallet and Blomstrand (Broggerhalvoya) peat profiles were composed of a peat developed in a nutrient enriched and wet tundra environment of steep birdcliffs. Pollen concentrations were low, Brassicaceae pollen dominated the whole profile. In contrast, the Ny Alesund and Isdammen profiles contained high pollen concentrations and suggest a nutrient-poor, dry tundra environment. Pollen of the polar willow, Salix polaris, occurred commonly throughout all four peat profiles. In the relatively high resolution (10 years per peat core sample) analysis of the Ny Alesund core, starting before or at the beginning of the Little Ice Age (LIA, 16th-mid 19th century), dominance of Saxifraga oppositifolia indicates a cold and dry climate, followed by a decline of Saxifraga oppositifolia and gradual increase of Salix polaris after the LIA, which indicates a moist and milder climate.

Is pollen morphology of Salix polaris affected by enhanced UV-B irradiation? Results from a field experiment in High Arctic tundra

This study tested the hypothesis that the thickness of the pollen wall will increase in response to enhanced UV-B irradiation, by examining the effect of enhanced UV-B irradiance on the pollen morphology of Salix polaris Wahlem. grown in a field experiment on the Arctic tundra of Svalbard. Measurements of pollen morphology were conducted by light microscopy on plants grown at two sites, Adventdalen and Isdammen. Salix vegetation was grown under control, enhanced UV-A, and two enhanced UV-B (simulating 15 and 30% reduction in the thickness of the stratospheric ozone layer) treatments. At the Adventdalen site, pollen wall thickness significantly increased under enhanced UV-A and UV-B treatments compared with the control. A thicker pollen wall helps to prevent damage by UV-B radiation of the DNA of the pollen. In contrast, plants at the Isdammen site did not exhibit any significant pollen morphological response to the enhanced UV treatments. The inconsistency in plant response to enhanced UV treatments between the two sites may be explained by greater habitat heterogeneity at the Isdammen site; abiotic soil conditions including nutrient and water availability may also have an influence on pollen morphology.