Effects Of UVR Research Articles

Introduction to Milestones in Photobiology

Electromagnetic radiation, encompassing UV, visible, and infrared radiation, has a major impact on human health. Sunlight, the major environmental agent to which humans are exposed, is responsible for the energy required to sustain life and stimulates the generation of vitamin D3 from the precursor 7-dehydrocholesterol. Sun exposure has been used for millennia as a therapeutic agent to treat dermatological and nondermatological disease. In addition, the advent of artificial nonlaser and laser light sources has further expanded the scope of diseases amenable to phototherapy beyond what natural sunlight can do. This form of radiant energy can also have nefarious effects. Acutely, it can trigger an erythema response in the skin (sunburn), and chronic exposure can cause photoaging of the skin, non-melanoma skin cancer (squamous cell and basal cell carcinoma), and melanoma. Investigation into the biological effects of nonionizing electromagnetic radiation on the skin has identified hitherto unsuspected actions of this form of radiant energy. For example, UVR is now known to influence immunological process, which may help explain its role in skin cancer, the pathogenesis of photosensitivity diseases, and its actions as a therapeutic agent. Infrared radiation, the cutaneous health effects of which had largely been thought to be limited to causing the rare condition ‘erythema ab igne’, now is recognized as a contributor to photoaging of the skin and may have a role as a therapeutic agent. Not surprisingly, because the skin bears the major burden of its impact, the consequences of UVR, visible light, and infrared radiation have been of particular interest to scientists who conduct research on the skin. Many of the ground-breaking observations with respect to cancer biology, the use of lasers, photoaging, and photoimmunology, to name a few, are derived from studies in the skin. The new knowledge generated from research in this area has led to a greater understanding of the biological effects of UVR on the skin and in disease pathogenesis and to improved therapeutic modalities. The Milestones in Photobiology presented here provide a brief overview of where we are and the prospects of photobiology for the future. The author states no conflict of interest. Elmets CA (2013) Introduction to Milestones in Photobiology. J Invest Dermatol 133: E1.

Responses of tropical plankton communities from the Mexican Caribbean to solar ultraviolet radiation exposure and increased temperature

The aim of this study was to evaluate the effects of UVR on growth and taxonomic composition of tropical plankton communities in a scenario of increased temperature and ultraviolet radiation. Water samples were collected from a reef lagoon in the Mexican Caribbean (20.5° N, 86.5° W) during July 2010 and grown for 16days in microcosms under two natural radiation treatments: a) PAB (PAR+UV-A+UV-B, 280–700nm) and, b) P, (PAR, 400–700nm) and two temperature conditions: a) ambient (28°C), and, b) increased (ambient+3°C). A differential factorial response of the studied variables among the main taxonomic groups and more frequent species was found. The biomass of dinoflagellates and colorless plankton was negatively affected by UVR while the increased temperature had negative effects on diatom biomass and cell abundance. During the experimental period there were changes in the contribution of each taxonomic group. At ambient temperature there was a shift from a flagellate- to a diatom-dominated community; whereas at increased temperature diatoms co-dominated with flagellates. UVR exposure decreased the contribution of naked dinoflagellates (>20μm) and cryptophytes. On the other hand, the most frequent diatom, Cylindrotheca closterium was negatively affected at increased temperature, while small chlorophytes (<10μm), which were one of the dominant groups of flagellates, contributed significantly to the biomass at increased temperature at the end of the experiment. Synergistic effects of UVR and temperature were only detected at the species level in large diatoms (>20μm; e.g. Leptocylindrus sp. and Amphora sp.) and in cryptophytes (>10μm). Our results suggest that planktonic assemblages from the Mexican Caribbean are generally well-adapted to the high UVR fluxes and temperature with some species being positively influenced by increased temperature. However there are exceptions with some species being negatively affected by UVR, increased temperature or the combination of both factors. Therefore, our results indicate that under the high radiation conditions of tropical oceans, changes in community structure in terms of taxonomic composition and size distribution would occur in a scenario of global climate change.

Influence of seasonal variables associated with climate change on photochemical diurnal cycles of marine phytoplankton from Patagonia (Argentina)

The effects of temperature and ultraviolet radiation (UVR; 280–400 nm) on seasonal succession in phytoplankton assemblages of Patagonia (Argentina) were studied in the context of global change. Samples collected during pre‐bloom, bloom onset, bloom, and spring were exposed to in situ and increased (+4°C) temperatures and solar radiation with and without UVR. Daily cycles of effective photochemical quantum yield exhibited a pattern of high values in the morning, decreasing towards noon, and increasing in the afternoon. The decrease in yields towards noon as the season progressed increased from 30% in the pre‐bloom to 80% in the spring; in the latter there were significant differences between radiation treatments under both temperature conditions. The highest inhibition rates were during the bloom, whereas the highest recovery rates were during the spring. Inhibition rates were generally higher in treatments exposed to UVR in comparison to photosynthetically active radiation‐only treatments and some stages of the succession exhibited an additional temperature effect. Increasing temperatures had little effect on pre‐bloom communities but helped to counteract the magnitude of the yield decrease during the bloom onset. However, during the bloom and in the spring, temperature and UVR acted synergistically, increasing the overall photochemical inhibition. Feedback mechanisms of increased temperatures causing a shallower mixing depth will expose phytoplankton to higher radiation, which will have a negative effect on the bloom and on spring assemblages. Due to the differential effects of solar UVR and increased temperature on phytoplankton, future studies should consider the repercussions on higher trophic levels.

Cercarial survival in an intertidal trematode: a multifactorial experiment with temperature, salinity and ultraviolet radiation

Parasite transmission takes place in the context of a multitude of simultaneously fluctuating environmental factors. As a particularly vulnerable step in the transmission, trematode cercariae are directly exposed to ambient conditions during their search for a host. Here, we investigated the survival of cercariae of the intertidal trematode Maritrema novaezealandensis in a multifactorial experiment (2 × 2 × 2 design) with temperature (20 and 30°C), salinity (35 and 40practical salinity units (psu)) and ultraviolet radiation (UVR; exposed and not exposed) as main factors. All factors had significant effects, with cercariae dying faster at the higher temperature, increased salinity and when exposed to UVR. Full activity ceased within ~6h in all treatments at 30°C, except at 35psu under no exposure to UV; in all other treatments full activity was maintained for >6h. Several factor interactions were identified, of which the interactive negative effect of temperature and UVR was the most important. These results imply that conditions during the main transmission window of M. novaezealandensis are highly challenging for cercariae. Our findings highlight the importance of considering multiple environmental factors in the study of parasite transmission to gain a more ecologically relevant understanding of transmission dynamics.

Role of p53 in antioxidative stress in melanocyte exposed to UV or H2O2

Objective To study the effects of UVR or H2O2 on the expression of p53 in human melanocytes,and that of nutlin-3 and PFT-α on the DNA oxidative damage,and to investigate the role of p53 in the antioxidative stress.Methods The effect of UVR,H2O2,nutlin-3 and PFT-α on the expression of p53 of human melanocytes was detected by Western blot analysis,and that of nutlin-3 and PFT-α on UVR or H2O2 DNA damage assessed by single cell electrophoresis (comet assay).Determination of the effect of nutlin-3 on H2O2 DNA damage was detected by γ-H2AX immunofluorescence.Results UVR and H2O2 could induce p53 protein expression,accompanied by increased phosphorylation of p53 on serine 15 residue,and nutlin-3 and PFT-α could induce and inhibit p53 protein in human melanocytes respectively; nutlin-3 decreased the tail moment of DNA oxidative damage of UVR or H2O2 in human melanocytes,but PFT-α increased the tail moment of DNA oxidative damage of UVR or H2O2 in human melanocytes,and there were significant differences among the control and exposed groups; nutlin-3 decreased expression of γ-H2AX.Conclusions p53 plays a very important role in the antioxidative stress in melanocyte exposed to UV or H2O2. Key words: Human melanocyte; p53; Nutlin-3; p53 inhibitor (PFT-α); DNA oxidative damage

Proteomic Responses of Sea Urchin Embryos to Stressful Ultraviolet Radiation

Solar ultraviolet radiation (UVR, 290-400 nm) penetrates into seawater and can harm shallow-dwelling and planktonic marine organisms. Studies dating back to the 1930s revealed that echinoids, especially sea urchin embryos, are powerful models for deciphering the effects of UVR on embryonic development and how embryos defend themselves against UV-induced damage. In addition to providing a large number of synchronously developing embryos amenable to cellular, biochemical, molecular, and single-cell analyses, the purple sea urchin, Strongylocentrotus purpuratus, also offers an annotated genome. Together, these aspects allow for the in-depth study of molecular and biochemical signatures of UVR stress. Here, we review the effects of UVR on embryonic development, focusing on the early-cleavage stages, and begin to integrate data regarding single-protein responses with comprehensive proteomic assessments. Proteomic studies reveal changes in levels of post-translational modifications to proteins that respond to UVR, and identify proteins that can then be interrogated as putative targets or components of stress-response pathways. These responsive proteins are distributed among systems upon which targeted studies can now begin to be mapped. Post-transcriptional and translational controls may provide early embryos with a rapid, fine-tuned response to stress during early stages, especially during pre-blastula stages that rely primarily on maternally derived defenses rather than on responses through zygotic gene transcription.

Molecular Response to Ultraviolet Radiation Exposure in Fish Embryos: Implications for Survival and Morphological Development

UVR exposure is known to cause developmental defects in a variety of organisms including aquatic species but little is known about the underlying molecular mechanisms. In this work we used zebrafish (Danio rerio) embryos as a model system to characterize the UVR effects on fish species. Larval viability was measured for embryos exposed to several UVR spectral treatments by using a solar simulator lamp and an array of UV cutoff filters under controlled conditions in the laboratory. Survival rate and occurrence of development abnormalities, mainly caudal (posterior) notochord bending/torsion, were seriously affected in UV-exposed larvae reaching values of 53% and 72%, respectively, compared with non-UV-exposed larvae after 6 days postfertilization (dpf). In order to elucidate the molecular mechanisms involved, a matricellular glycoprotein named osteonectin and the expression of a DNA-repair related gene, p53, were studied in relation to UVR exposure. The results indicate that osteonectin and p53 expression were increased under UVR exposure due to wavelengths shorter than 335 nm (i.e. mainly UVB) and 350 nm (i.e. short UVA and UVB), respectively. Furthermore, parallel experiments with microinjections of osteonectin-capped RNA showed that malformations induced by osteonectin overexpression were similar to those observed after a UVR exposure. Consequently this study shows a potential role of osteonectin in morphological deformities induced by solar UV radiation in zebrafish embryos.

Sublethal effects of ultraviolet radiation on crab larvae of Cyrtograpsus altimanus

Ultraviolet radiation (UVR, 280–400nm) is known to be lethal to several aquatic species; however, more subtle, ‘sublethal’ effects of UVR have recently received more attention. Larvae of the crab Cyrtograpsus altimanus are a transient component of the plankton community in the Atlantic northern Patagonia (Argentina) and thus they may be exposed to solar UVR in both open and coastal waters. The aim of this study was to determine if previous sublethal UVR exposure on larvae of C. altimanus affects development, body size and motility. Larvae which were pre-exposed to UVR had a delay/absence of molting from Zoea I to Zoea II, coupled to arrested body growth, but showed enhanced swimming behavior. In contrast, the control group (i.e., exposed only to visible light) molted from Zoea I to Zoea II after 6–9days, with a significant increase in body size, and did not change their motility. Since hatching of this species occurs in summer (i.e., season with highest UVR levels) our results suggest that, by significantly affecting development, growth and motility, natural UVR may influence the plankton–benthos coupling in coastal waters.

Increase in Rubisco activity and gene expression due to elevated temperature partially counteracts ultraviolet radiation–induced photoinhibition in the marine diatom Thalassiosira weissflogii

We performed outdoor experiments to evaluate the effect of temperature on photoinhibition properties in the cosmopolitan diatom Thalassiosira weissflogii. Cultures were exposed to solar radiation with or without ultraviolet radiation (UVR, 280–400 nm), UV‐A (320–400 nm), and UV‐B (280–320 nm) at both 20°C and 25°C. Four possible cellular mechanisms involved in UVR stress were simultaneously addressed: carbon incorporation, chlorophyll a fluorescence of photosystem II, xanthophyll cycle activity, and ribulose‐1,5‐biphosphate carboxylase : oxygenase (Rubisco) activity and gene expression. Experiments consisted of daily cycles (i.e., the daylight period) and short‐term incubations (i.e., 1 h centered on local noon). Samples incubated at 25°C had significantly less UVR‐induced inhibition of carbon fixation and effective photochemical quantum yield compared to those incubated at 20°C. At 25°C Rubisco activity and gene expression were significantly higher than at 20°C. The higher Rubisco activity and gene expression were correlated with less dissipation of excess energy, evaluated via non‐photochemical quenching, and the de‐epoxidation state of the xanthophyll pigments, as more photons could be processed. An increase in temperature due to climate change would partially counteract the negative effects of UVR by increasing the response of metabolic pathways, such as those involved in Rubisco. This, in turn, may have important consequences for the ecosystem, as higher production (due to more Rubisco activity) could be expected under a scenario of global warming.

The Effects of UV Radiation on Chloroplast Clumping and Photosynthesis in the SeagrassHalophila stipulaceaGrown under High-PAR Conditions

Since potentially harmful ultraviolet radiation (UVR, 280–400 nm) and high photosynthetically active radiation (PAR, 400–700 nm) are present in the shallow waters of the Gulf of Aqaba where part of the seagrassHalophila stipulacea'spopulation thrives, we examined the effects of high PAR with and without UVR on its photosynthesis and midday chloroplast “clumping phenomenon” (Sharon and Beer 2008). It was found that midday clumping occurred only under high PAR in the presence of UVR, which resulted in a 44% reduction in the absorption cross section (or absorption factor, AF) of the leaves and, accordingly, a parallel lowering of midday electron transport rates (ETR). In addition, UVR had a direct effect on the photosynthetic apparatus by lowering quantum yields and, thus, ETRs, while pigment relations remained unaltered. We conclude that the potentially harmful effects of UVR and high PAR on the photosynthetic apparatus ofHalophila stipulaceaare mitigated by their activation of chloroplast clumping, which functions as a means of protecting most chloroplasts from high irradiances, including UVR.

Temperature benefits the photosynthetic performance of the diatoms Chaetoceros gracilis and Thalassiosira weissflogii when exposed to UVR

The aim of this study was to assess the combined effects of temperature and UVR on the photosynthesis performance of two diatoms – Chaetoceros gracilis and Thalassiosira weissflogii. In particular, we evaluated the role of UVR in inducing photoinhibition and the potential mitigation of this negative effect by an increase in temperature. Cultures were pre-acclimated at two temperatures – 18 °C and 23 °C – and exposed to different radiation treatments – UVR + PAR (280–700 nm); UV-A + PAR (315–700 nm) and PAR only (400–700 nm) under two temperatures: 18 °C (local surface summer water temperature) and 23 °C (simulating a potential increase estimated by the year 2100). Exposure to natural solar radiation resulted in UVR-induced photoinhibition that was significantly higher in T. weissflogii than in C. gracilis. Both species benefited from the higher temperature (23 °C) resulting in a lower photoinhibition as compared to samples exposed at 18 °C. Inter-specific differences were determined in regard to the heat dissipation processes (NPQ) which were higher at high temperatures, and much more evident in C. gracilis than in T. weissflogii. The analyses of inhibition and recovery rates under different irradiances indicate that the balance between negative (inhibition) and positive (repair-dissipation) effects shifted towards a more positive balance with increasing temperature. Our results highlight for a beneficial effect of temperature on photosynthesis performance during exposure to UVR, although important inter-specific differences are found, probably due to differences in cell size as well as in their distribution within the oceanic realm (i.e., coastal versus oceanic species).

Combined Effects of UVR and Temperature on the Survival of Crab Larvae (Zoea I) from Patagonia: The Role of UV-Absorbing Compounds

The aim of our study was to assess the combined impact of UVR (280–400 nm) and temperature on the first larval stage (Zoea I) of three crab species from the Patagonian coast: Cyrtograpsus altimanus, C. angulatus, and Leucippa pentagona. We determined the survival response of newly hatched Zoea I after being exposed for 8–10 h under a solar simulator (Hönle SOL 1200) at 15 and 20 °C. There was no mortality due to Photosynthetic Active Radiation (PAR, 400–700 nm) or ultraviolet-A radiation (UV-A, 315–400 nm), and all the observed mortality was due to ultraviolet-B radiation (UV-B, 280–315 nm). The data of larval mortality relative to exposure time was best fit using a sigmoid curve. Based on this curve, a threshold (Th) and the lethal dose for 50% mortality (LD50) were determined for each species. Based on the Th and LD50, C. altimanus was found to be the most resistant species, while L. pentagona was found to be the most sensitive to UV-B. For both species of Cyrtograpsus, mortality was significantly lower at 20 °C than at 15 °C; however, no significant differences between the two temperature treatments were found in L. pentagona. Bioaccumulation of UV-absorbing compounds in the gonads and larvae of C. altimanus, and to a lesser extent in C. angulatus, might have contributed for counteracting the impact of UV-B. However, most of the resilience to UV-B observed with the increase in temperature might be due to an increase in metabolic activity caused by a repair mechanism mediated by enzymes.

Seasonal succession and UV sensitivity of marine bacterioplankton at an Antarctic coastal site

Despite extensive microbial biodiversity studies around the globe, studies focusing on diversity and community composition of Bacteria in Antarctic coastal regions are still scarce. Here, we studied the diversity and development of bacterioplankton communities from Prydz Bay (Eastern Antarctic) during spring and early summer 2002-2003. Additionally, we investigated the possible shaping effects of solar UV radiation (UV-R: 280-400 nm) on bacterioplankton communities incubated for 13-14 days in 650-L minicosm tanks. Ribosomal DNA sequence analysis of the natural bacterioplankton communities revealed an initial springtime community composed of three evenly abundant bacterial classes: Cytophaga-Flavobacteria-Bacteroidetes (CFB), Gammaproteobacteria and Alphaproteobacteria. At the end of spring, a shift occurred toward a CFB-dominated community, most likely a response to the onset of a springtime phytoplankton bloom. The tail end of Prydz Bay clone library diversity revealed sequences related to Deltaproteobacteria, Verrucomicrobiales, Planctomycetes, Gemmatimonadetes and an unclassified bacterium (ANT4E12). Minicosm experiments showed that incubation time was the principal determinant of bacterial community composition and that UV-R treatment significantly changed the composition in only two of the four experiments. Thus, the successional maturity of the microbial community in our minicosm studies appears to be a greater determinant of bacterial community composition rather than the nonprofound and subtle effects of UV-R.

Stoichiometric dietary constraints influence the response of copepods to ultraviolet radiation‐induced oxidative stress

We carried out field experiments in two clear mountain lakes of both hemispheres (Lake Los Cántaros, Patagonia, Argentina, and Lake La Caldera, Sierra Nevada, Spain) performing a full factorial design (light × nutrients: unfiltered sun light (ultraviolet radiation treatment [UVR]) and screened sunlight (&gt; 380 nm; photosynthetically active radiation treatment), with and without nutrient enrichment. We analyzed the direct effect of UVR on enzymatic antioxidant responses (catalase [CAT], glutathione S‐transferase [GST], and glutathione reductase [GR]) of two calanoid copepod species‐Boeckella gibbosa and Mixodiaptomus laciniatus‐ and the indirect effects of food quality (carbon : nutrient ratio) potentially affecting body elemental compositions and hence enzymatic activities. Responses for the three enzymes were different: GST increased its activity under UVR exposure in the two copepods, CAT activity was null and showed no response, and GR activity differed between species. Light treatments also affected sestonic elemental ratios; UVR exposure lowered carbon : phosphorus (C : P) ratios, which in turn affected the C: P elemental compositions of the copepods. However, nutrient addition had different effects on the two species; it did not affect final somatic C: P ratio of B. gibbosa but had a substantial effect on body elemental composition of M. laciniatus. Finally, the relationship between grazer’s C: P ratio and GST antioxidant enzyme activity was negative. UVR and nutrient inputs affected food quality, grazer somatic stoichiometry, and subsequently enzymatic responses. The ability of calanoid copepods to overcome increased UVR may depend, at least for GST, on the elemental nutrient balance of the food.

A broad‐spectrum sunscreen prevents cumulative damage from repeated exposure to sub‐erythemal solar ultraviolet radiation representative of temperate latitudes

We have previously shown the detrimental effects of 19 sub-erythemal exposures to daily ultraviolet radiation (DUVR, which mimics non-extreme exposure conditions), delivered over 4 weeks to volunteers. This source had UVA (320-400 nm) to UVB (290-320 nm) irradiance ratio of 25, instead of that close to 10 that is typically the case with solar-simulated radiation (SSR) that represents summer global sunlight with a clear sky and quasi-zenith solar irradiance. Here, we report on an extension of this previous study, in which we evaluated the photoprotection afforded by a broad-spectrum daily-care product with a low-sun protection factor (SPF 8, UVA-PF 7 and 3* rated UVA protection). We assessed cellular and molecular markers of photodamage that are relevant to skin cancer and photoageing. This study shows that biological effects of repeated exposure to DUVR can be prevented by a broad-spectrum daily-care product and that the level of protection afforded varies with the studied endpoint. Efficient daily UVR protection, as provided by a broad-spectrum daily-care product, is necessary to prevent the 'silent' sub-erythemal cumulative effects of UVR from inadvertent sun exposure.

The Effect of Ultraviolet Radiation (Type B) on Decubitus Ulcers

Pressure ulcers heal slowly and this often results in prolonged hospitalization. Wound infection delays healing in decubitus ulcers and standard treatment include wound dressing and use of antibiotics. However, there is increasing resistance of bacteria to antibiotics. The purpose of this study was to determine the effects of ultraviolet radiation (UVB) on the healing of decubitus ulcers. The study was also designed to learn the effect of UVR (Type B) on bacteria. Methods: Ten subjects with ascertained bilateral pressure sores (6 at the gluteal region and 4 at the heels) on the left lower extremities were recruited for this study. The left limbs (experimental limbs) were radiated with UVR (B) coupled with normal wound dressing while the right (control) limbs only received normal wound dressing for 6 weeks. The data were analyzed using descriptive and non-parametric inferential statistics (Kruska Wallis test). Results: There was 78.9% decrease in the mean surface area of the decubitus ulcers of the experimental (left) limbs while there was only 37.4% decrease in the mean surface area of the decubitus ulcers of the control (right) limbs. Similarly, there was 74.7% decrease in the mean volume of the decubitus ulcers of the experimental (left) limbs while there was only 46.3% decrease in the mean volume of decubitus ulcers of the control (right) limbs. The result of the Kruska Wallis test showed that there was significant decrease in the growth of bacteria (X² = 37.01, P&lt;0.00) and significant increase in the growth of epithelial cells (X² = 36.65, P&lt; 0.00) in the decubitus ulcers that were irradiated with UVR. Conclusion: It was concluded that ultraviolet radiation (Type B) had significant effects in destroying bacteria and also promoting wound healing.

Rosmarinus officinalis Extract Inhibits Human Melanoma Cell Growth

Rosmarinus officinalis L. is receiving increasing attention due to its anti-inflammatory and antioxidative constituents. Our recent studies showed that R. officinalis extract, containing 31.7% of carnosic acid, was able to counteract the deleterious effects of UV-R, by protecting plasmid DNA from hydroxyl radicals generated by UV-A. In this work, we evaluated the effects of this extract on pBR322 DNA cleavage induced by nitric oxide, and the growth inhibitory activity against two human melanoma cell lines, M14 and A375. The extract showed a protective effect on plasmid DNA damage, and at concentrations of 10-80 microg/mL was able to reduce significantly (p<0.001) the growth (MTT assay) of both melanoma cell lines. In addition, our results indicate that apoptotic cell demise is induced in M14 and A375 cells. No statistically significant increase in LDH release was observed in melanoma cells, correlated to a fragmentation of genomic DNA, determined by COMET assay.

The water column as an attenuating factor of the UVR effects on bacteria from a coastal Antarctic marine environment

The water column as an attenuating factor of the UVR effects on bacteria from a coastal Antarctic marine environment

Does ultraviolet radiation affect the xanthophyll cycle in marine phytoplankton?

This Perspective summarizes the state of knowledge of the impact of ultraviolet radiation on the photoprotective xanthophyll cycle in marine phytoplankton. Excess photosynthetically active radiation (PAR; 400-700 nm) and ultraviolet radiation (UVR; 280-400 nm) affect various cellular processes and can potentially lead to reduced growth or viability loss in situ. Algae deploy photoprotective mechanisms that limit the hazardous effects of excess light exposure. Xanthophyll cycle pigments play a crucial role in photoprotection via the development of non-photochemical fluorescence quenching (NPQ) during excess radiation exposure. Research on the interacting effects of excess PAR and UVR exposure on xanthophyll cycle pigment synthesis and xanthophyll cycle activity has produced contrasting views. The current contribution summarizes research on photoprotection via photoregulation (xanthophyll cycle activity) and photoacclimation (adjustment of the xanthophyll cycle pigment pool) for marine phytoplankton. Subsequently, UVR effects on the xanthophyll cycle and on xanthophyll cycle pigment pools are discussed and results of supporting experiments with the common diatom Thalassiosira weissflogii are presented. We show that UVR exposure may enhance xanthophyll cycle pigment synthesis. This suggests that UVR-induced reduction in de-epoxidation state does not necessarily imply reduced energy dissipating potential.

Effects of ultraviolet radiation on the productivity and composition of freshwater phytoplankton communities

The net influence of ultraviolet radiation (UVR; 280-400 nm) on freshwater phytoplankton communities depends on the photon flux density, duration, and spectral quality of exposure and the UVR sensitivity of the assemblage in terms of photosynthetic impairment, biochemical composition, and nutrient assimilation mechanisms. Such effects are mitigated to varying degrees by photoacclimation and selective adaptation at the community level. Variation in UVR penetration among lakes is considerable, largely due to differences in chromophoric dissolved organic matter concentrations. Documented losses of areal daily primary production in lakes due to UVR range from negligible (2.5%) to appreciable (26%). UVR has the potential to alter algal biochemical composition and therefore indirectly affect higher trophic levels. There is evidence that algal nutritional status can influence UVR sensitivity, and that UVR can inhibit uptake and assimilation of inorganic nutrients, but results have been inconsistent. Taxonomic variability in susceptibility to the effects of UVR exists, and likely reflects variation in cell size and shape, concentrations of photoprotective pigments, and capacity to repair UVR photodamage. Suggestions for future research include: (1) resolution of taxon-specific UVR responses by way of single-cell techniques (e.g. enzyme-labelled fluorescence assays, microscope-based variable fluorometers) and (2) systematic comparative studies to link UVR exposure in natural habitats to community responses using the biological weighting function modelling approach. A more robust understanding of how sensitivity to UVR varies according to taxon and habitat is needed if predictions of its role in ecosystem functioning, particularly in connection with climate change, are to be meaningful.