Effects Of UVBR Research Articles

Effects of enhanced temperature and ultraviolet B radiation on a natural plankton community of the Beagle Channel (southern Argentina): a mesocosm study

Marine planktonic communities can be affected by increased temperatures associated with global climate change, as well as by increased ultraviolet B radiation (UVBR, 280-320 nm) through stratospheric ozone layer thinning. We studied individual and combined effects of increased temperature and UVBR on the plankton community of the Beagle Channel, southern Patagonia, Argentina. Eight 2 m3 mesocosms were exposed to 4 treatments (with 2 replicates) during 10 d: (1) control (natural temperature and UVBR), (2) increased UVBR (simulating a 60% decrease in stratospheric ozone layer thickness), (3) increased temperature (+ 3°C), and (4) simultaneous increased temperature and UVBR (60% decrease in stratospheric ozone; + 3°C). Two distinct situations were observed with regard to phytoplankton biomass: bloom (Days 1-4) and post-bloom (Days 5-9). Significant decreases in micro-sized diatoms (>20 µm), bacteria, chlorophyll a, and particulate organic carbon concentrations were observed during the post-bloom in the enhanced temperature treatments relative to natural temperature, accompanied by significant increases in nanophytoplankton (10-20 µm, mainly prymnesiophytes). The decrease in micro-sized diatoms in the high temperature treatment may have been caused by a physiological effect of warming, although we do not have activity measurements to support this hypothesis. Prymnesiophytes benefited from micro-sized diatom reduction in their competition for resources. The bacterial decrease under warming may have been due to a change in the dissolved organic matter release caused by the observed change in phytoplankton composition. Overall, the rise in temperature affected the structure and total biomass of the communities, while no major effect of UVBR was observed on the plankton community.

Responses of the macroalgae Hypnea musciformis after in vitro exposure to UV-B

The in vitro effects of UVBR were investigated in apical segments of Hypnea musciformis. The plants were cultivated and exposed to photosynthetically active radiation (PAR) at 80μmolphotonsm−2s−1 and PAR+UVBR at 1.6Wm−2 at 3h per day for 7 days. Toluidine Blue reaction showed metachromatic granulations in vacuole, and Periodic Acid Schiff stain showed a decrease in the number of floridean starch grains. UVBR also caused changes in the ultrastructure of cortical cells, which included increased thickness of the cell wall, reduced intracellular spaces, changes in the cell contour, destruction of chloroplast internal organization, and rough endoplasmic reticula increase. The algae cultivated under PAR-only showed growth rates of 9.7%day−1, while algae exposed to PAR+UVBR grew only 3.2%day−1. Furthermore, compared with control algae, phycobiliprotein contents (phycoerythrin, phycocyanin, and allophycocyanin) were observed to decrease after PAR+UVBR. However, chlorophyll a levels were not significantly different (ANOVA, P=0.52) after exposure to PAR+UVBR. As a photoprotective adaptation strategy against UVB damage, an increase of 58.9% phenolic compounds and 3.6% of carotenoids was observed. Overall, these results lead to the conclusion that both ultrastructural damage and observable changes in metabolism occurred in H. musciformis after only 3h of daily UVB exposure over a 7-d experimental period.

Impact of ultraviolet-B radiation on planktonic fish larvae: Alteration of the osmoregulatory function

Coastal marine ecosystems are submitted to variations of several abiotic and biotic parameters, some of them related to global change. Among them the ultraviolet-B (UV-B) radiation (UVBR: 280–320nm) may strongly impact planktonic fish larvae. The consequences of an increase of UVBR on the osmoregulatory function of Dicentrarchus labrax larvae have been investigated in this study. In young larvae of D. labrax, as in other teleosts, osmoregulation depends on tegumentary ion transporting cells, or ionocytes, mainly located on the skin of the trunk and of the yolk sac. As early D. labrax larvae passively drift in the top water column, ionocytes are exposed to solar radiation. The effect of UVBR on larval osmoregulation in seawater was evaluated through nanoosmometric measurements of the blood osmolality after exposure to different UV-B treatments. A loss of osmoregulatory capability occured in larvae after 2 days of low (50μWcm−2: 4h L/20h D) and medium (80μWcm−2: 4h L/20h D) UVBR exposure. Compared to control larvae kept in the darkness, a significant increase in blood osmolality, abnormal behavior and high mortalities were detected in larvae exposed to UVBR from 2 days on. At the cellular level, an important decrease in abundance of tegumentary ionocytes and mucous cells was observed after 2 days of exposure to UVBR. In the ionocytes, two major osmoeffectors were immunolocalized, the Na+/K+-ATPase and the Na+/K+/2Cl− cotransporter. Compared to controls, the fluorescent immunostaining was lower in UVBR-exposed larvae. We hypothesize that the impaired osmoregulation in UVBR-exposed larvae originates from the lower number of tegumentary ionocytes and mucous cells. This alteration of the osmoregulatory function could negatively impact the survival of young larvae at the surface water exposed to UVBR.

Effects of Ultraviolet B Radiation on the Cornea of Adult Male Albino Rats and the Possible Role of Lornoxicam

Introduction: Ultraviolet Radiation (UVR) represents a significant environmental and occupational hazard to human beings especially after the ozone hole. Lornoxicam is a strong non-steroidal anti-inflammatory drug (NSAID) with few side effects. Aim of the Work: This work aimed to clarify effects of UVBR on the cornea of adult male albino rats and the possible role of lornoxicam. Materials and Methods: Thirty adult male albino rats were used. They were divided into three main groups: Control; Lornoxicam treated and UV irradiated which was further subdivided into 3 subgroups. On sacrifice, cornea was processed for histological, immunohistochemical and morphometrical studies. Results: Cornea of UV irradiated rats revealed epithelial thinning with cellular degeneration, exfoliation and metaplasia. Bowman's membrane was focally interrupted or absent. Stroma showed irregularly arranged widely separated collagen fibers, degenerated few keratocytes with neovascularization, interstitial hemorrhage and cellular infiltration. Ultrastructurally, epithelial cells showed nuclear membrane irregularities, chromatin condensation, mitochondrial degeneration and loss of rER. Immunohistochemically, epithelial cells and keratocytes showed marked expression of caspase-3 protein in their cytoplasm. Morphometrically, there was a highly significant decrease in epithelial thickness, area % of stroma and number of keratocytes. Rats left to recover without treatment showed mild improvement, while treatment of irradiated rats with lornoxicam for one week after exposure showed nearly normal histological, ultrastructural, and immunohistochemical pictures. Conclusion: Lornoxicam (a cheap, available tolerable NSAID) could ameliorate UVB induced corneal changes. So it could be considered as a curative measure of the cornea against UVB.

Ecotoxicological Effects of Combined UVB and Organic Contaminants in Coastal Waters: A Review

ABSTRACTOrganisms living in coastal waters are exposed to anthropogenic contaminants from terrestrial drainage, ice melting and maritime traffic and to enhanced UVB radiation (UVBR; 280–320 nm) caused by decreased concentrations of ozone in the stratosphere. This article reviews available information about the combined effects of UVBR and selected hydrosoluble contaminants potentially present in surface waters on marine species and especially on plankton community structure in high‐latitude coastal zones. Effects of UVBR on three selected pesticides (Atrazine, carbaryl and Acifluorfen) and possible induction of phototoxicity are reviewed. Most toxicological studies have been conducted under laboratory conditions with questionable relevance for coastal marine ecosystems. Similarly, photoactivation of polycyclic aromatic hydrocarbons (PAHs) has been closely examined and reported effects on aquatic species summarized. Experiments with field‐sampled communities demonstrated the complexity and the difficulty in determining the impact of multiple stressors on an aquatic ecosystem, even for ecosystems simplified by eliminating large grazers and fish. Nutrient status, specific composition and light history have influenced the different responses of planktonic assemblages exposed to enhanced UVBR and water‐soluble fraction (WSF) from crude oil or to tributyltin. Plankton assemblages subjected to changes in the ozone hole were physiologically stressed and more susceptible to WSF tox‐icity than communities from less enhanced UVBR‐impacted sites. A close relationship between phytoplankton assemblages and bacteria was observed in all experiments in mesocosms. A contaminant‐induced phytoplankton crash after a bloom event may release important carbon and nutrient sources for bacteria. The magnitude of phytoplanktonic mortality induced by a contaminant probably influenced how rapidly bacteria grew over time. The transition from a herbivorous food web to a microbial food web has significant ecological implications for carbon cycling and energy flow in pelagic systems. A high phytoplankton mortality implies a situation in which the potential for downward carbon export from surface waters is high. In contrast, high bacterial enrichment implies that the phytoplankton carbon is largely recycled in surface waters through a microbial loop and does not contribute significantly to sinking particle flux. The most ecologically relevant results were obtained with mesocosm studies using field‐collected communities. The enhancement of hydrocarbon toxicity in the presence of a high level of UVBR cannot be described as being a synergistic or an additive effect, because the WSF alone is not toxic and may even be beneficial by increasing bacterial activity. This is a case in which one stressor has the ability to modify another stressor to cause it to be toxic to target organisms. These abiotically induced interactions may be important for biological communities exposed to extreme conditions when physical, chemical or photochemical reactions modify the nature of environmental stressors before they interact with biological functions. The need for models on the impacts of multiple stressors on biodiversity and ecosystem functioning is emphasized.

Ultraviolet B‐photoprotection Efficiency of Mesocosm‐enclosed Natural Phytoplankton Communities from Different Latitudes: Rimouski (Canada) and Ubatuba (Brazil)

Photoprotection against UV-B radiation (UVBR; 280-320 nm) was examined in natural phytoplankton communities from two coastal environments at different latitudes: temperate Rimouski (Canada) and tropical Ubatuba (Brazil). Mesocosm experiments were performed at these sites to examine the response of phytoplankton to increases in UVBR that corresponded to local depletions of 30% and 60% in atmospheric ozone levels (low and high UVBR treatments, respectively). A fluorescence method using a pulse amplitude modulation fluorometer (Xe-PAM, Walz, Germany) with selective UV filters was used to estimate photoprotection, and these results were compared with an index of mycosporine-like amino acid (MAA) concentrations determined using spectrophotometry of methanol extracts. The present study provided the first evidence, to our knowledge, of the suitability of this in vivo fluorescence method for the estimation of UV photoprotection efficiency in natural phytoplankton. No significant differences were found for most of the variables analyzed between the light treatments used at both sites, but differences were found between sites throughout the duration of the experiments. Vertical mixing, used to maintain cells in suspension, likely alleviated serious UVBR-induced damage during both experiments by reducing the length of time of exposure to the highest UVBR irradiances at the surface. In Rimouski, this was the main factor minimizing the effects of treatment, because optical properties of the coastal seawater rapidly attenuated UVBR throughout the water column of the ca 2 m deep mesocosms. In this location, synthesis of MAAs and photoprotective pigments likely contributed to the observed phototolerance of phytoplankton and, hence, to their growth; however, in a comparison of the UVBR treatments, these variables showed no differences. In Ubatuba, where nutrient concentrations were significantly lower than those in Rimouski, light attenuation was less than that in Rimouski and UVBR reached the bottom of the mesocosms. UVBR penetration and the forced vertical mixing of the cells, without the possibility of vertical migration below this photostress zone, resulted in photo-inhibition, because confinement in the mesocosms forced cells to remain constantly exposed to high levels of irradiance during the daytime. Hence, additional effects of UVBR were masked in this experiment, because cells were damaged too much and phytoplankton populations were rapidly declining. There was also an overall preservation of MAAs, in contrast with chlorophyll (Chl) degradation, in spite of the fact that this UV screening was not sufficient to counteract photo-inhibition, which suggests an important role for these molecules, either in the overall photoprotection strategy or in other physiological processes. Altogether, local water characteristics, namely attenuation, mixing, and nutrients concentration, can strongly modulate the photoprotection strategies used by natural phytoplankton populations in coastal environments.

Ecotoxicological Effects of Combined UVB and Organic Contaminants in Coastal Waters: A Review

Organisms living in coastal waters are exposed to anthropogenic contaminants from terrestrial drainage, ice melting and maritime traffic and to enhanced UVB radiation (UVBR; 280-320 nm) caused by decreased concentrations of ozone in the stratosphere. This article reviews available information about the combined effects of UVBR and selected hydrosoluble contaminants potentially present in surface waters on marine species and especially on plankton community structure in high-latitude coastal zones. Effects of UVBR on three selected pesticides (Atrazine, carbaryl and Acifluorfen) and possible induction of phototoxicity are reviewed. Most toxicological studies have been conducted under laboratory conditions with questionable relevance for coastal marine ecosystems. Similarly, photoactivation of polycyclic aromatic hydrocarbons (PAHs) has been closely examined and reported effects on aquatic species summarized. Experiments with field-sampled communities demonstrated the complexity and the difficulty in determining the impact of multiple stressors on an aquatic ecosystem, even for ecosystems simplified by eliminating large grazers and fish. Nutrient status, specific composition and light history have influenced the different responses of planktonic assemblages exposed to enhanced UVBR and water-soluble fraction (WSF) from crude oil or to tributyltin. Plankton assemblages subjected to changes in the ozone hole were physiologically stressed and more susceptible to WSF toxicity than communities from less enhanced UVBR-impacted sites. A close relationship between phytoplankton assemblages and bacteria was observed in all experiments in mesocosms. A contaminant-induced phytoplankton crash after a bloom event may release important carbon and nutrient sources for bacteria. The magnitude of phytoplanktonic mortality induced by a contaminant probably influenced how rapidly bacteria grew over time. The transition from a herbivorous food web to a microbial food web has significant ecological implications for carbon cycling and energy flow in pelagic systems. A high phytoplankton mortality implies a situation in which the potential for downward carbon export from surface waters is high. In contrast, high bacterial enrichment implies that the phytoplankton carbon is largely recycled in surface waters through a microbial loop and does not contribute significantly to sinking particle flux. The most ecologically relevant results were obtained with mesocosm studies using field-collected communities. The enhancement of hydrocarbon toxicity in the presence of a high level of UVBR cannot be described as being a synergistic or an additive effect, because the WSF alone is not toxic and may even be beneficial by increasing bacterial activity. This is a case in which one stressor has the ability to modify another stressor to cause it to be toxic to target organisms. These abiotically induced interactions may be important for biological communities exposed to extreme conditions when physical, chemical or photochemical reactions modify the nature of environmental stressors before they interact with biological functions. The need for models on the impacts of multiple stressors on biodiversity and ecosystem functioning is emphasized.

The effects of UV radiation on photosynthesis in an Antarctic diatom ( Thalassiosira sp.): Does vertical mixing matter?

The reduction of Antarctic stratospheric ozone results in significant increases in ultraviolet B radiation (UVB-R, 280–320 nm) reaching ocean's surface, potentially damaging phytoplankton. Several studies refer to the negative direct and indirect effects of UVB-R and ultraviolet A (UVA-R, 320–400 nm, which is not modified by ozone concentration) on different targets within algal cells. There are, however, internal and external processes, like vertical mixing, which can in part counteract such effects. The hypothesis that vertical mixing is a significant factor reducing the negative effects of ultraviolet radiation (UV-R, 280–400 nm) on planktonic algae photosynthesis was tested at Potter Cove (South Shetland Is., Antarctica). Three laboratory (solar simulator, SOLSI) and two field (natural Sun exposure) experiments were conducted. Vertical mixing was studied exposing cells of Thalassiosira sp., a typically bloom forming diatom in Antarctic waters, to variable light conditions simulating 6 h cycles (Mix treatment), whereas incubations at two fixed depths were used as controls (0.5 and 5 m, S fix and D fix treatments, respectively). Light effects were studied for each of the previous exposure conditions considering three treatments: PAR-T (exposure to PAR, photosynthetic active radiation, 400–700 nm), UVA-T (exposure to PAR and UVA-R) and UVB-T (exposure to PAR, UVA-R and UVB-R). During SOLSI experiments no significant differences were found between the different light treatments under simulated normal and medium ozone concentrations. Under low ozone conditions, 40% reduction in photosynthesis was observed in the UVB-T for surface incubations. In contrast, no significant differences were observed among the light treatments under mixing conditions. Field and laboratory experiments showed similar results. However, during one of the field experiments when ozone was low, not only S fix but Mix incubations presented a significant reduction in photosynthesis, suggesting that vertical mixing under such conditions was not efficient enough to prevent harmful UVB-R effects. On the other hand, during a day with high insulation and normal ozone, but with elevated absorption of light in the water column, no significant effects of any of the studied factors were detected. In conclusion, vertical mixing was shown to play a significant role in protecting algae under low ozone concentrations, lessening photoinhibition by UVB radiation. The differences between laboratory and field experiments are discussed in terms of the relative significance of UVB-R dose and dose rate on both types of experiments.

Ultraviolet-B radiation effects on natural phytoplankton assemblages of central San Francisco Bay

Since the discovery of a depletion of the stratospheric ozone layer over Antarctica in 1979, scientific attention has been directed towards the effects of increased doses of ultraviolet radiation on phytoplankton in other ecosystems. Little is known about the effects of ultraviolet-B (280–320 nm) radiation (UVBR) on temperate estuarine phytoplankton. Freshly collected phytoplankton samples from Central San Francisco Bay were exposed to ambient UVBR in quartz bottles and monitored for biomass and nutrient uptake rates for comparison with phytoplankton dispensed into bottles made of polycarbonate that effectively filtered out the UVBR to evaluate response to natural UVBR exposure. Short-term (10–12 h) exposure experiments were carried out monthly from October 1998 to October 1999. No significant effect of UVBR on chlorophylla concentrations was found but a clear deleterious effect of UVBR on nutrient uptake was observed.

Non-synergistic effects of water-soluble crude oil and enhanced ultraviolet-B radiation on a natural plankton assemblage

The present study demonstrates the effects of the water-soluble fraction (WSF) of a crude oil, enhanced ultraviolet-B radiation (UVBR: 280 to 320 nm), and the combination of WSF and en- hanced UVBR on a natural plankton assemblage (<150 μm) isolated from the lower St. Lawrence Estu- ary. To study the separate and dual effects of WSF and UVBR, 12 microcosms (9 l) were immersed in the water column of larger mesocosms (polyethylene bags; 1800 l), providing 4 treatments, each in triplicate: (1) NUVBR + WSF (natural UVBR with WSF), (2) HUVBR + WSF (enhanced UVBR with WSF), (3) NUVBR (natural UVBR without WSF), and (4) HUVBR (enhanced UVBR without WSF). Dur- ing 5 d we monitored the incident radiation, WSF and nutrient concentrations, abundance and produc- tion of heterotrophic bacteria and phytoplankton. Strong deleterious effects of WSF and lower effects of UVBR were observed on the phytoplankton assemblage, with a decrease in growth rates accompa- nied by an increase in mean cell size which reflected a perturbation of the cell division cycle. Using the NUVBR treatement as reference conditions, the above effects resulted in a reduction of 84, 79 and 60% of total abundance of the phytoplankton fraction <20 μm in the HUVBR + WSF, NUVBR + WSF and HUVBR treatments, respectively. Significant higher values of bacterial abundances were ob- served in the WSF-added treatments compared to NUVBR without WSF. However, bacterial thymi- dine incorporation exhibited diel variations, suggesting cumulative UVBR-induced DNA and/or PAH- induced DNA damages, and possible repair mechanisms with the co-occurrence of more available growth substrates from stressed phytoplankton. The absence of significant differences between both WSF-added treatments under the 2 different UVBR conditions suggests that there is no additive inter- action between WSF and UVBR. This study provides therefore the first evidence of a non-synergistic interaction between both stresses, and suggests that UVBR-induced effects on marine microorganisms can be completely masked by the strong deleterious effects of soluble petroleum hydrocarbons.

Sensitivity and acclimation to UV radiation of zoospores from five species of Laminariales from the Arctic

Spores of five Laminariales from Arctic Spitsbergen were exposed in the laboratory to photosynthetically active radiation (PAR; 400–700 nm), PAR+UVA radiation (UVAR; 320–400 nm) and PAR+UVAR+UVB radiation (UVBR; 280–320 nm). Subsequently, germination was monitored over periods of 3, 6 and 9 days. The investigated species were the upper sublittoral Saccorhiza dermatodea, the upper to mid-sublittoral Alaria esculenta and Laminaria digitata, the mid-sublittoral L. saccharina and the lower sublittoral L. solidungula. The germination capacity decreased sharply after 16 h exposure to PAR+UVAR+UVBR in all species. However, S. dermatodea was able to recover from the damaging effects of UVBR. There was also a small increase in percentage germination of A. esculenta 6–9 days after the treatment. No recovery was evident in the other species. After 8 h exposure to PAR+UVA+UVB, L. digitata recovered completely, and L. saccharina and L. solidungula, partially. The only species susceptible to PAR+UVAR was L. solidungula. One prominent cytological feature of UVR-exposed spores was the enlargement of phenolic vesicles (physodes) (particularly seen in S. dermatodea and A. esculenta), which may have a protective function against UVR. Pilot experiments under natural irradiance conditions indicate that the PAR component of solar radiation exerts an additional stress. Overall the data show that zoospores of the species from the upper sublittoral are less sensitive to UVR or have the capacity to recover from UV stress in contrast to species from deeper waters, probably due to their UV protective and repair capabilities.

Ultraviolet radiation modulates nuclear factor kappa B activation in human lens epithelial cells.

Exposure to ultraviolet radiation (UVR) is a known risk factor for cataract, but the molecular mechanisms involved have not been elucidated. We hypothesized that exposure to UVR would modulate the activation of nuclear factor kappa-B (NF-kappa B) within the human lens epithelium, since NF-kappa B is a key regulator of cellular responses to UVR stress in other cell types. Human lens epithelial (HLE) cells were exposed to acute physiological doses of ultraviolet A (UVAR), B (UVBR), C (UVCR) radiation, or interleukin-1 beta (IL-1 beta) and NF-kappa B activation was measured by electrophoretic shift assay (EMSA). Phosphorylation of I kappa B in response to UVAR was measured by Western blotting. Irradiation of HLE cells with UVAR (0-1100 J/m(2)) did not reduce cell survival, while UVBR (400-1600 J/m(2)) and UVCR (300-900 J/m(2)) significantly reduced HLE cell survival. EMSA analysis of HLE nuclear proteins indicated activation of NF-kappa B, but not activator protein-1 (AP-1), by UVAR. The effects of UVBR and UVCR were less pronounced. Exposure of HLE cells to UVAR (0-900 J/m(2)) followed by a 30-min incubation resulted in a dose-dependent activation of NF-kappa B. UVAR-induced NF-kappa B activation in HLE cells was evident 10 min postirradiation, maximal at 60 min and returned to control levels by 120 min. Western blot analysis of phosphorylation of the NF-kappa B inhibitory protein, I kappa B, revealed that UVAR activates NF-kappa B via a mechanism involving the phosphorylation of I kappa B-alpha; this effect was dose-dependent. Supershift analysis demonstrated that UVAR and IL-1 beta activate the transcriptionally active p65/p50 NF-kappa B dimer. These studies demonstrate that UVAR activates NF-kappa B in HLE cells in a time- and dose-dependent manner via signaling through I kappa B-alpha. The activation of NF-kappa B in HLE cells by UVAR may have implications for the development and progression of cataract and other related ocular disorders.

Effects of reduced UV radiation on a microbenthic community during a microcosm experiment

A microcosm experiment was conducted over a 77 d period (from 6 July to 21 Septem- ber 1999) to investigate the response of a microbenthic community to the long-term reduction of ambient ultraviolet-B (UVBR, 280 to 320 nm) and ultraviolet-A (UVAR, 320 to 400 nm) radiation. Intact sediment cores were harvested from a muddy intertidal flat in the lower St. Lawrence Estuary (Quebec, Canada) and placed in an outdoor flow-through system under 3 treatments: ambient solar radiation, reduced UVBR and reduced UVR (280 to 400 nm). Both autotrophic (primary production, microalgal biomass, accessory pigments, diatom composition and abundance and UVR absorbing compounds) and heterotrophic (meiofaunal abundance) components were investigated. It was found that neither nematode nor ontogenic stages of harpacticoid copepod abundances were affected by the treatments. The temporal variations of the nauplius, copepodite and copepod populations corre- spond to the normal ontogenic evolution of harpacticoids. The microphytobenthic community, domi- nated by small (≤15 µm) pennate diatoms, presented significantly higher carbon fixation under UVR protected treatments on Days 14 and 21, suggesting a simultaneously detrimental but weak effect of UVBR and UVAR on photosynthesis. Occurring in very low concentrations in the sediment, UVR absorbing compounds did not seem to be a major UVR-attenuation mechanism within the micro- benthic community. The screening of UVBR and UVR also resulted in a stepwise decrease of micro- algal biomass on Days 7, 21, 28, 35 and 42, and of diatom abundance on Day 35. The simultaneous accumulation of pheopigments likely reflected an enhanced grazing pressure under both UV- shielded treatments, presumably by microfaunal grazers. The fact that these noticeable changes were observed between the 3 treatments implies that both UVBR and UVAR influence the micro- phytobenthic community. There was a lack of treatment effect during the second half of the experi- ment when UVR fluxes showed their normal seasonal decrease. Thus, our results indicate that effects of ambient UVR on microbenthos occur only under high solar irradiance. During this period, both ambient UVBR and UVAR exerted a controlling effect on the microalgal standing stock in muddy intertidal flats in the lower St. Lawrence Estuary.

Further Characterization of UVB Radiation Effects on Langerhans Cells: Altered Expression of the Costimulatory Molecules B7‐1 and B7‐2

We have reported previously that low-dose UVB radiation (UVBR, 50-200 J/m2) perturbs the antigen-presenting cell (APC) function of murine Langerhans cells (LC) by interfering with yet undefined costimulatory signals. In this study, we investigated (1) the effects of UVBR on the expression of the costimulatory molecules B7-1 and B7-2 on murine LC, (2) the functional consequences of defective B7-1 and B7-2 signalling on primary and secondary T-cell responses induced by LC and (3) the mechanism by which UVBR interferes with B7-1 and B7-2 expression. Ultraviolet-B radiation dose-dependently inhibited the culture-induced upregulation of B7-1 and B7-2 on LC from both UVB-susceptible (UVBs, C57BL/6) and UVB-resistant (UVBR, Balb/c) mice and abrogated their capacity to stimulate proliferation of naive alloreactive T cells and of the KLH (keyhole limpet hemocyanin)-specific T helper (Th)1 clone HDK-1. The UVBR-induced suppression of B7-1 and B7-2 on LC and their perturbed APC function were related, because exogenous triggering of the B7/CD28 pathway with a stimulatory monoclonal antibody (mAb) for CD28 to UVB-irradiated LC partially restored T-cell proliferation. Such reconstitution was not observed when the mAb was added to killed LC, indicating that the UVBR-induced suppression of APC function was not due to lethal effects on LC. Conditioned supernatants from UVB-irradiated epidermal cells did not inhibit the functional upregulation of B7-1 and B7-2, suggesting that UVBR inhibits B7-1 and B7-2 upregulation by acting directly on LC and not by altering LC costimulatory function via release of soluble immunosuppressive factors. In conclusion, UVBR distorts the functional expression of B7-1 and B7-2 on LC from both UVBS and UVBR mice, thereby contributing to the failure of UVB-irradiated LC to stimulate resting alloreactive T cells or KLH-specific Th1 cells.

Further Characterization of UVB Radiation Effects on Langerhans Cells: Altered Expression of the Costimulatory Molecules B7-1 and B7-2

We have reported previously that low-dose UVB radiation (UVBR, 50-200 J/m2) perturbs the antigen-presenting cell (APC) function of murine Langerhans cells (LC) by interfering with yet undefined costimulatory signals. In this study, we investigated (1) the effects of UVBR on the expression of the costimulatory molecules B7-1 and B7-2 on murine LC, (2) the functional consequences of defective B7-1 and B7-2 signalling on primary and secondary T-cell responses induced by LC and (3) the mechanism by which UVBR interferes with B7-1 and B7-2 expression. Ultraviolet-B radiation dose-dependently inhibited the culture-induced upregulation of B7-1 and B7-2 on LC from both UVB-susceptible (UVBs, C57BL/6) and UVB-resistant (UVBR, Balb/c) mice and abrogated their capacity to stimulate proliferation of naive alloreactive T cells and of the KLH (keyhole limpet hemocyanin)-specific T helper (Th)1 clone HDK-1. The UVBR-induced suppression of B7-1 and B7-2 on LC and their perturbed APC function were related, because exogenous triggering of the B7/CD28 pathway with a stimulatory monoclonal antibody (mAb) for CD28 to UVB-irradiated LC partially restored T-cell proliferation. Such reconstitution was not observed when the mAb was added to killed LC, indicating that the UVBR-induced suppression of APC function was not due to lethal effects on LC. Conditioned supernatants from UVB-irradiated epidermal cells did not inhibit the functional upregulation of B7-1 and B7-2, suggesting that UVBR inhibits B7-1 and B7-2 upregulation by acting directly on LC and not by altering LC costimulatory function via release of soluble immunosuppressive factors. In conclusion, UVBR distorts the functional expression of B7-1 and B7-2 on LC from both UVBs and UVBR mice, thereby contributing to the failure of UVB-irradiated LC to stimulate resting alloreactive T cells or KLH-specific Thl cells.

Further Characterization of UVB Radiation Effects on Langerhans Cells: Altered Expression of the Costimulatory Molecules B7-1 and B7-2

We have reported previously that low-dose UVB radiation (UVBR, 50-200 J/m2) perturbs the antigen-presenting cell (APC) function of murine Langerhans cells (LC) by interfering with yet undefined costimulatory signals. In this study, we investigated (1) the effects of UVBR on the expression of the costimulatory molecules B7-1 and B7-2 on murine LC, (2) the functional consequences of defective B7-1 and B7-2 signalling on primary and secondary T-cell responses induced by LC and (3) the mechanism by which UVBR interferes with B7-1 and B7-2 expression. Ultraviolet-B radiation dose-dependently inhibited the culture-induced upregulation of B7-1 and B7-2 on LC from both UVB-susceptible (UVBs, C57BL/6) and UVB-resistant (UVBR, Balb/c) mice and abrogated their capacity to stimulate proliferation of naive alloreactive T cells and of the KLH (keyhole limpet hemocyanin)-specific T helper (Th)1 clone HDK-1. The UVBR-induced suppression of B7-1 and B7-2 on LC and their perturbed APC function were related, because exogenous triggering of the B7/CD28 pathway with a stimulatory monoclonal antibody (mAb) for CD28 to UVB-irradiated LC partially restored T-cell proliferation. Such reconstitution was not observed when the mAb was added to killed LC, indicating that the UVBR-induced suppression of APC function was not due to lethal effects on LC. Conditioned supernatants from UVB-irradiated epidermal cells did not inhibit the functional upregulation of B7-1 and B7-2, suggesting that UVBR inhibits B7-1 and B7-2 upregulation by acting directly on LC and not by altering LC costimulatory function via release of soluble immunosuppressive factors. In conclusion, UVBR distorts the functional expression of B7-1 and B7-2 on LC from both UVBs and UVBR mice, thereby contributing to the failure of UVB-irradiated LC to stimulate resting alloreactive T cells or KLH-specific Thl cells.

Interactions between nutritional status and long-term responses to ultraviolet-B radiation stress in a marine diatom

Influences of nutritional status on the photoinhibitory effects of ultraviolet-B radiation (UVBR: 290 to 320 nm) on the specific growth rates (μobs) and biomass of Phaeodactylum tricornutum were determined using nutrient-replete batch cultures and nutrient-limited continuous cultures. P. tricornutum cultures were exposed to UVBR doses representative of current mid-latitude and ozone-depletion intensities. Specific growth rates and biomass were inhibited from 2 to 16% by UVBR during nutrient-replete growth. However, no effect of UVBR on μobs or biomass was detectable when nutrient limitation exceeded the potential for limitation by UVBR. Thus, a competitive interaction appears to occur between macronutrient stress and UVBR stress, such that μobs and biomass will be determined by the most limiting factor. Our results suggest that measurable decreases in phytoplankton μobs and biomass from UVBR are most likely in nutrient-rich areas of the ocean, while these parameters may not be appropriate for measuring UVBR stress in regions of nutrient limitation.