Effects Of ultraviolet-B Radiation Research Articles

Direct and indirect effects of ultraviolet-B radiation on soil biota, decomposition and nutrient fluxes in dune grassland soil systems

Enhanced UV radiation did not show any effect on the decomposition of a mixed litter of the dune grassland plant species Calamagrostis epigeios and Carex arenaria. Also, leaching of nutrients from lysimeters filled with dune grassland soils was not affected by enhanced UV radiation. Negative UV effects on the fungal biomass in the first part of the experiment were later reversed into positive ones. Clear effects of both UV-A and UV-B were found on Collembola, both on total number of individuals and on the number of species. The decreased number of species under UV radiation could have been due to a decrease in UV-sensitive species. The role of pigmentation is discussed.

Effects of UVB radiation on a marine microphytobenthic community growing on a sand‐substratum under different nutrient conditions

The effect of ultraviolet‐B radiation (UVBR) on a microphytobenthic community, dominated by diatoms, was studied under different nutrient conditions in a 9 day outdoor experiment on the Swedish west coast. The microalgal assemblage was isolated from the sediment and resettled onto acid‐cleaned sand placed in petridishes. The experimental treatments were: “ambient” or “enhanced” UVBR with no nutrient addition, “ambient” or “enhanced” UVBR with nutrient addition (N, P, Si). Enhanced UVBR (+15%) was provided by a computer‐controlled system. Primary productivity, carbon allocation, chlorophyll a (Chl a) concentrations, composition of algae and pigments and intra‐ and extracellular carbohydrate fractions were measured. Most UVBR effects were seen in treatments without nutrient addition. Exposure to enhanced UVBR resulted in statistically significant decreases in primary productivity, Chl a and in the biomass of Haslea ostrearia and Nitzschia spp. The relative amount of carbon allocated to proteins increased when exposed to enhanced UVBR. The effect of enhanced UVBR on microalgae subjected to nutrient addition was less pronounced, and observed for Chl a, algal intracellular storage of carbohydrates (glucans) and concentration of extracellular “colloidal” carbohydrates. Enhanced UVBR + nutrients resulted in a significantly greater ratio between glucan and total carbohydrates and a decreased concentration of colloidal carbohydrates compared to the ambient UVBR + nutrients treatment. These results indicate that availability of inorganic nutrients acts to mitigate the negative effects of UVBR on microphytobenthic communities and that UVBR acts as a selective force during early growth and succession.

Ultraviolet B radiation downregulates inducible nitric oxide synthase expression induced by interferon-gamma or tumor necrosis factor-alpha in murine keratinocyte Pam 212 cells.

Ultraviolet radiation causes inflammation characterized by erythema and swelling, but also exhibits antiinflammatory effects which have led to the use of ultraviolet B radiation (UVBR) and psoralen plus ultraviolet A (PUVA) in the treatment of psoriasis, chronic severe atopic dermatitis and uremic pruritus. In inflammatory dermatoses, a pathogenic role of nitric oxide (NO) derived from inducible nitric oxide synthase (iNOS) has been suggested. To elucidate how UVBR regulates iNOS expression in skin under inflammatory conditions, we investigated the effect of UVBR on NO production and iNOS expression in cultured murine keratinocyte Pam 212 cells stimulated with interferon-gamma (IFN-gamma) or tumor necrosis factor-alpha (TNF-alpha). Low doses of UVBR significantly suppressed IFN-gamma- or TNF-alpha-induced NO production. UVBR also downregulated IFN-gamma- or TNF-alpha-induced iNOS expression at both the mRNA level and the protein level. These findings suggest the possibility that the down-regulatory effect of UVBR on IFN-gamma- or TNF-alpha-induced iNOS expression may, in part, explain the antiinflammatory and therapeutic properties of UVBR in inflammatory dermatoses.

Tannins Protect Against Skin Tumor Promotion Induced by Ultraviolet-B Radiation in Hairless Mice

We recently showed that Tarapod tannic acid (TA), a hydrolyzable tannin extracted from the pods of the Tara tree (Caesalpinia spinosa), was more effective than other tannins tested at inhibiting ultraviolet-B (UV-B)-stimulated hydrogen peroxide activity (an indirect measure of free radicals) in the skin of hairless mice. We also found that Tarapod TA inhibited UV-B-induced ornithine decarboxylase activity and UV-B-stimulated DNA synthesis, two biochemical markers linked to the skin tumor-promoting ability of this physical carcinogen. For this reason, we examined the effect of topical application, force feeding (gavage), and intraperitoneal injections of Tarapod TA on mouse skin chronically treated with UV-B light. Mice were initiated by a single topical application of 7,12-dimethylbenz[a]anthracene (50 nmol) and promoted by two weekly treatments with UV-B light (250 mJ/cm2) for 25 weeks. Topical application of Tarapod TA, 20 minutes before irradiation, resulted in a dose-dependent inhibition of tumor incidence (number of mice with tumors) and tumor yield (number of tumors/ mouse), with 8 mg of TA inhibiting tumor yield by 70% at Week 25. Intraperitoneal injections of low doses (10 mg/kg mouse body wt), but not of high doses (25 mg/kg body wt), of TA afforded protection against UV-B-induced papillomas. However, the protection by intraperitoneal injection was lower than that observed by topical application: 10 mg/kg body wt of TA reduced tumor yield by 55%. The force feeding of 10 mg of Tarapod TA before irradiation failed to significantly inhibit the yield of tumors at the end of the experiment but delayed tumor appearance by six weeks. These results suggest that plant tannins administered topically or injected intraperitoneally reduce the tumor-promoting effects of UV-B radiation and thus could be useful photoprotectants.

Population differences in Trifolium repens L. response to ultraviolet-B radiation: foliar chemistry and consequences for two lepidopteran herbivores.

White clover growing in New Zealand is experiencing increasing levels of ultraviolet-B (UV-B) radiation as a result of ozone depletion. We evaluated the effects of UV-B radiation on the foliar chemistry of two populations of white clover (Trifolium repens L.), 'Huia' and 'Tienshan,' and the consequences for the performance of armyworms (Spodoptera litura) and cutworms (Graphania mutans). Plants were grown in controlled environment rooms with and without supplemental UV-B radiation at a dose of 13.3 kJ m-2 day-1, corresponding to a 25% mid-summer ozone depletion above Palmerston North, New Zealand. In both white clover populations, UV-B radiation elicited changes in foliar chemistry, including slight increases in nitrogen concentrations and decreases in carbohydrate concentrations. In addition, the 'Huia' population showed decreases in fiber concentrations and marked increases in cyanogenic activity. No change in UV-absorbing compounds was detected in either population. Long- and short-term feeding trials were conducted to assess dietary effects on insect growth, consumption, and food utilization. Changes in the performance of both insect species were generally small. The most pronounced effect was a 36% reduction in weight of S. litura after 2 weeks of feeding on Huia grown at high UV, but larval development times were only slightly prolonged and pupal weights were unaffected. S. litura short-term performance was affected by differences in white clover population. The long-term performance of G. mutans was not affected and its short-term performance (stadium duration and consumption rate) was only marginally affected by the high-UV treatment. We conclude that the effects of elevated UV-B radiation on white clover plant chemistry can be specific to certain plant populations. The differences in sensitivity of the two generalist insect species suggest that effects may also be specific to certain plant-herbivore associations. These results indicate that future UV-B herbivory studies should examine genotypic effects in both plants and animals.

Effects of ultraviolet-B radiation on simultaneous carbon and nitrogen transport rates by estuarine phytoplankton during a week-long mesocosm study

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 199:69-81 (2000) - doi:10.3354/meps199069 Effects of ultraviolet B radiation on simultaneous carbon and nitrogen transport rates by estuarine phytoplankton during a week-long mesocosm study Laure Mousseau1,*, Michel Gosselin1, Maurice Levasseur2, Serge Demers1, Juliette Fauchot1, Suzanne Roy1, Piedad Zulema Villegas1, Behzad Mostajir1 1Institut des sciences de la mer de Rimouski (ISMER), Université du Québec à Rimouski, 310 allée des Ursulines, Rimouski, Québec G5L 3A1, Canada 2Institut Maurice-Lamontagne, Ministère des Pêches et des Océans, CP 1000, Mont-Joli, Québec G5L 3Z4, Canada *Present address: Observatoire Océanologique, BP 28, 06230 Villefranche-sur-Mer, France. E-mail: mousseau@obs-vlfr.fr ABSTRACT: The effect of UV B radiation on photosynthesis and nitrogen uptake by an estuarine phytoplankton community was investigated during a week long experiment, conducted in 8 mesocosms under varying conditions of UV-B radiation: reduced UV-B, natural radiation, and 2 levels of enhanced UV-B. Twice a day, dissolved inorganic carbon (13C) and total dissolved nitrogen (15N) transport rates were estimated simultaneously from in situ incubations. Irrespective of the treatment, phytoplankton biomass (chlorophyll a) and primary production increased over the first 3 d. Subsequently, nitrate and silicate depletion resulted in a decrease in algal biomass and productivity. Enhanced UV-B radiation was deleterious to chlorophyll a specific transport rates of C and N when compared to reduced and natural UV B. The C:N transport ratios, as well as the POC:PON ratios, were generally not affected by enhanced or reduced UV-B. In the enhanced UV-B treatments, carbon transport rates were often significantly higher in the afternoon than in the morning, suggesting that phytoplankton exposed to UV B developed photoprotective mechanisms against UV radiation on a daily basis. A shift in the algal community assemblage from diatoms (>10 µm) to small flagellates (5-10 µm) was observed during the study. Small flagellates were less sensitive to the UV B treatments than diatoms, whose abundance decreased under reduced and enhanced UV B. Results from this study suggest that UV B exposure on a daily basis could change the chlorophyll a specific transport rates of C and N and alter the structure of the phytoplankton community. KEY WORDS: Mesocosms · Nitrogen transport · Photoinhibition · Photosynthesis · Phytoplankton · St. Lawrence Estuary · UV B radiation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 199. Publication date: June 26, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.

The impacts of UV-B radiation on the regeneration of a sub-arctic heath community

The effects of ultraviolet-B radiation on regeneration after disturbance of a natural sub-arctic heathland have been investigated. Areas of pristine dwarf shrub heath were denuded of all above ground biomass in 1992 and exposed to enhanced UV-B (simulating a 15% depletion of the ozone layer). The resulting regenerated stem and leaf growth parameters were measured after four years on three dwarf shrubs, Vaccinium myrtillus, V. uliginosum and V. vitis-idaea and the grass Calamagrostis lapponica; leaves of the three dwarf shrubs were also analysed for UV-absorbing compounds and carbohydrates. Regeneration irrespective of treatment was slow, with Empetrum hermaphroditum failing to regenerate at all. Vaccinium myrtillus showed the most rapid regeneration attaining much of its original biomass in four years. There was a significant interaction between UV-B and year of regeneration in V. myrtillus; annual stem length increment showed an initial stimulation of 75% under enhanced UV-B in the first year of regeneration while a reduction of 16% was observed in the fourth year. Both V. uliginosum and V. vitis-idaea showed a reduction in annual stem length increment as regeneration progressed with a greater than 50% reduction in stem increment in the fourth year of regeneration compared to the first. Vaccinium uliginosum also showed an initial reduction in stem length increment of 40% under enhanced UV-B. None of the species were affected by enhanced UV-B in terms of total regenerated stem and leaf biomass or UV-absorbing compounds in regenerated leaf tissue. Total leaf carbohydrate and the ethanol/water soluble fraction in V. uliginosum were significantly increased by 29% and 31% respectively under enhanced UV-B. This suggests either a stimulation of photosynthesis or a reduction in sink size for photo-assimilates. Results are discussed in the context of the extremely slow regeneration of sub-arctic heath communities and the implications of contrasting UV-B effects on the regenerative ability of different species.

A Substance p Agonist Acts as an Adjuvant to Promote Hapten-Specific Skin Immunity

Because substance p (SP) has been reported to be released from cutaneous sensory nerve endings after hapten application, we determined whether SP participates in contact hypersensitivity (CH) induction by using a SP agonist, GR73632 or delta-Aminovaleryl [Pro9, N-Me-Leu10]-substance P(7-11) and a SP antagonist, spantide I. When injected intradermally, SP agonist enhanced CH induced by conventional, but not optimal, sensitizing doses of hapten. By contrast, SP antagonist inhibited the induction of CH by optimal sensitizing doses of hapten. Moreover, SP agonist promoted CH induction and prevented tolerance when hapten was painted on skin exposed to acute, low-dose ultraviolet-B radiation. Intradermally injected SP agonist altered neither the density nor the morphology of epidermal Langerhans cells, implying that SP agonist enhanced the generation of hapten-specific immunogenic signals from the dermis. It is proposed that SP is a natural "adjuvant" that promotes the induction of CH within normal skin. Although exogenous SP agonist can prevent impaired CH and tolerance after ultraviolet-B radiation, the susceptibility of native SP to local neuropeptidases renders the neuropeptide unable to prevent the deleterious effects of ultraviolet-B radiation on cutaneous immunity.

Effects of Ultraviolet-B Radiation on Needle Anatomy and Morphology of Western Larch, Interior Spruce and Lodgepole Pine

Ultraviolet-B (UV-B) radiation (280–320 nm) is increasing in the biosphere because anthropogenic ozone scavengers diffusing to the stratosphere are depleting the protective stratospheric ozone layer (Kerr and McElroy, 1993). For every 1% decrease in stratospheric 142ozone there is a 2% increase in UV-B reaching the earth’s surface (Caldwell, 1979). This study describes morphological and anatomical changes in needles of ecologically and economically important conifers exposed to differential UV-B doses.

Bacterivory of a natural heterotrophic protozoan community exposed to different intensities of ultraviolet-B radiation

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 20:59-74 (1999) - doi:10.3354/ame020059 Bacterivory of a natural heterotrophic protozoan community exposed to different intensities of ultraviolet-B radiation Khaled Chatila1, Serge Demers1,*, Behzad Mostajir1, Michel Gosselin1, Jean-Pierre Chanut1, Patrick Monfort2 1Groupe de Recherche en Environnement Côtier, Institut des Sciences de la Mer de Rimouski (ISMER), Université du Québec à Rimouski, 310 Allée des Ursulines, Rimouski (Québec) G5L 3A1, Canada 2Laboratoire d'Hydrobiologie Marine et Continentale, Unité mixte de Recherche 'Écosystèmes lagunaires', Université Montpellier II, CNRS (UMR 5556), Case 093, 34095 Montpellier Cedex 05, France *Corresponding author. E-mail: serge_demers@uqar.uquebec.ca ABSTRACT: The effects of ultraviolet-B radiation (UVBR) on the bacterivory of a natural marine protozoan community were examined as part of a 7 d experiment designed to study the effects of different UVBR intensities on the summer planktonic assemblage of the lower St. Lawrence Estuary, Québec, Canada. The experiment was conducted in large containers (mesocosms) subjected to 1 of the following UVBR regimes: excluded UVBR (WUVB), natural UVBR (NUVB), and natural UVBR enhanced with either 2 lamps (LUVB) or 3 lamps (HUVB). Incubations with fluorescently labeled bacteria were conducted daily as a tool to understand the interaction between the potential bacterivores (heterotrophic ciliates and nanoflagellates) and bacteria within the studied system. UVBR intensities had no significant effects on the estimated clearance and ingestion rates (CR and IR, respectively) until Day 5 of the experiment. During the following 2 d, characterized by low nutrient concentration, both CR and IR decreased with the increase of the daily UVBR (at 305 and 320 nm) doses received. The maximum difference between treatments was observed on Day 7, where both clearance and ingestion rate values in the NUVB, LUVB and HUVB treatments were significantly lower than the WUVB treatment. Our data suggest that over a 1 d period and under conditions of high nutrient concentrations, protozoan bacterivory is not affected by UVBR increases. When nutrient concentrations become low, bacterivores become more susceptible to damaging UVBR effects. We think that the deterioration of food quality, itself resulting from the synergistic action of nutrients and UVBR stresses, is responsible for the increased sensitivity of bacterivores to UVBR. UVBR-induced decreases in bacterivory would represent a considerable loss to the higher tropic levels that feed upon bacterivores. KEY WORDS: Ultraviolet-B · Protozoa · Bacterivory · Bacterioplankton · Clearance rate · Ingestion rate · St. Lawrence Estuary Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 20, No. 1. Publication date: November 30, 1999 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1999 Inter-Research.

Methods for exposure of laboratory animals to ultraviolet radiation.

Two different sources of ultraviolet B (UVB) radiation, an electronically controlled UVB exposure unit, containing FS40 tubes, and a hand-held Kromayer lamp, were evaluated for actual irradiance in W/m2 and spectra (physical dosimetry and biological dosimetry (skin effects in rodents)). The technical studies of the FS40 sources demonstrated that the flux intensity of the lamps could be changed electronically, without affecting the spectrum. Thus it was possible to standardize UVB exposure electronically. The biologically effective doses of these sources were analysed in RIV-Tox Wistar rats and BALB/c mice. After low doses of UVB radiation, histopathological changes such as acanthosis, hyperkeratosis and dermal inflammation were observed in the skin without the presence of major side effects such as erythema and oedema. After higher doses of UVB radiation erythema and oedema were clearly visible. Quantitative studies showed that the minimal erythema dose, as a biological parameter, correlated well to the emission in J/m2. In addition, biological parameters such as acanthosis and inflammation in the skin correlated well to the actual exposure in J/m2 and were sensitive biomarkers for UVB-induced skin toxicity. Thus, in addition to minimal erythemal doses, acanthosis and inflammation may also be applied as biologically relevant doses for studies of the biological effects of UVB radiation.

A new concept of skin-associated lymphoid tissue (SALT): UVB light impaired cutaneous immunity reveals a prominent role for cutaneous nerves.

More than 20 years have passed since the concept that the skin has its own associated immune system was first proposed by Streilein. This proposal was advanced in part on evidence that cutaneous contact hypersensitivity (CH) reactions are closely correlated with Langerhans cells (LC). Recent reports have demonstrated that LC have neural connectivity with cutaneous nerve termini containing calcitonin gene-related peptide (CGRP), suggesting that a link exists between innervation and immune responses in the skin. Here we discuss the neural components which have recently been found to be participants in skin-associated lymphoid tissue (SALT). In part, discovery of a functional link between the nervous system and SALT is based on studies in which cutaneous immunity was impaired by ultraviolet-B radiation (UVR). The deleterious effects of UVR on cutaneous immunity include failed CH induction and promotion of hapten-specific tolerance, effects that are mediated by tumor necrosis factor-alpha and interleukin-10, respectively. The source of these cytokines after UVR appears to be dermal mast cells. Evidence indicates that mast cells are triggered to release these cytokines in response to CGRP, which is released from UVR-damaged cutaneous nerve endings. Moreover, a substance P agonist was able to reverse the deleterious effects of UVR on CH induction, rendering the mice able to develop intense CH. These observations indicate that two cell types not originally included in the SALT concept are critical to the functional integrity of cutaneous immunity: mast cells and cutaneous nerves. We propose that cutaneous nerves dictate whether antigen applied to or arising within skin will lead to sensitivity or tolerance.

HindIII Liposomes Suppress Delayed-Type Hypersensitivity Responses In Vivo and Induce Epidermal IL-10 In Vitro

AbstractConsiderable evidence suggests that ultraviolet-B (UV-B) radiation suppresses certain immune responses through the induction of cyclobutane pyrimidine dimers in DNA. To determine whether induction of other forms of DNA damage in the skin mimicked the immunosuppressive effects of UV-B radiation, we produced double-strand breaks in the DNA of epidermal cells with HindIII restriction endonuclease encapsulated in liposomes. Application of these liposomes, but not liposomes containing inactive HindIII or an irrelevant endonuclease, to the skin of C3H mice suppressed the induction of delayed-type hypersensitivity responses to Candida albicans and alloantigen and induced IL-10 production in the epidermis. Treatment of the Pam212 murine keratinocyte cell line with these liposomes in vitro induced immunosuppressive activity and IL-10 in culture supernatants. Unlike UV-B irradiation, however, HindIII in liposomes failed to induce suppressor T cell activity in vivo or in vitro. We conclude that double-strand breaks in DNA of epidermal cells can induce immunosuppression and up-regulate the production of immunomodulatory cytokines; however, either DNA damage alone does not account for all the immunosuppressive properties of UV-B irradiation, or cyclobutane pyrimidine dimers differ qualitatively from double-strand breaks in their biologic consequences. These studies raise the possibility that drugs causing DNA damage may induce cytokine dysregulation and immune suppression in addition to cytotoxicity.

Ultraviolet-B radiation effects on water relations, leaf development, and photosynthesis in droughted pea plants

The effects of ultraviolet-B (UV-B) radiation on water relations, leaf development, and gas-exchange characteristics in pea (Pisum sativum L. cv Meteor) plants subjected to drought were investigated. Plants grown throughout their development under a high irradiance of UV-B radiation (0.63 W m-2) were compared with those grown without UV-B radiation, and after 12 d one-half of the plants were subjected to 24 d of drought that resulted in mild water stress. UV-B radiation resulted in a decrease of adaxial stomatal conductance by approximately 65%, increasing stomatal limitation of CO2 uptake by 10 to 15%. However, there was no loss of mesophyll light-saturated photosynthetic activity. Growth in UV-B radiation resulted in large reductions of leaf area and plant biomass, which were associated with a decline in leaf cell numbers and cell division. UV-B radiation also inhibited epidermal cell expansion of the exposed surface of leaves. There was an interaction between UV-B radiation and drought treatments: UV-B radiation both delayed and reduced the severity of drought stress through reductions in plant water-loss rates, stomatal conductance, and leaf area.

Plants for environmental studies

The Effects of Ultra Violet-B Radiation on Higher Plants, B. Greenberg, M.I. Wilson, X.-D. Huang, C.L. Duxbury, K.E. Gerhardt, and R.W. Gensemer Radiation Effects on Plants, R.W. Holst and D.J. Nagel Plant-Water Interactions, J.L. Hatfield Plant Activation of Environmental Agents: The Utility of the Plant Cell/Microbe Coincubation Assay, M.J. Plewa, K.-Y. Seo, Y.-H. Ju, S.R. Smith, and E.D. Wagner Statistical Methods in Plant Environmental Studies, M. Ritter Water Quality and Aquatic Plants, M.A. Lewis and W. Wang Algal Indicators of Aquatic Ecosystem Conditions and Change, P.V. McCormick and J. Cairns Photosynthetic Electron Transport as a Bioassay, J. Gemel, B. Waters-Earhart, M.R. Ellersieck, A. Asfaw, G.F. Krause, V. Puri, and W.R. Lower Laboratory Bioassays with Microalgae, N. Nyholm and H.G. Peterson Aquatic Plant Communities for Impact Monitoring and Assessment, B.H. Hill Allium Test for Screening Chemicals Evaluation of Cytological Parameters, G. Fiskesjo The Use of Vascular Plants as Field Biomonitors, R.L. Powell Metal Accumulation by Aquatic Macrophytes, W. Wang and M.A. Lewis Bioaccumulation of Xenobiotic Organic Chemicals by Terrestrial Plants, O.J. Schwartz and L.W. Jones Uptake of Polycyclic Aromatic Hydrocarbons by Vegetation: A Review of Experimental Methods, T.A. Anderson, A.M. Hoylman, N.T. Edwards, and B. Walton Plant Uptake and Metabolism Polychlorinated Biphenyls (PCBs), R.K. Puri, Y. Qiuping, S. Kapila, W.R. Lower, and V. Puri Selection of Phytotoxicity Tests for Use in Ecological Risk Assessments, L.A. Kapustka Index

Effects of ultraviolet-B radiation on two arctic microbial food webs

Effects of ultraviolet-B radiation on two arctic microbial food webs

The changing irradiance environment: consequences for marine macrophyte physiology, productivity and ecology

Decreases in the concentration of ozone in the stratosphere are predicted to result in more biologically damaging ultraviolet-B radiation (UVBR) reaching the Earth's surface in the near future. The consequences for plant life of this small change in the solar spectrum are currently uncertain; this is particularly true for aquatic macrophytic algae. The aim of this review is to summarize the current knowledge of UVBR effects on macrophytes, and to highlight areas for future research. An overview of published underwater UVBR measurements shows that penetration of this waveband is low in the coastal waters where most macroalgae are found. Knowledge of UVBR targets in macroalgae is poor, and biological weighting functions have yet to be established. Studies of higher plants and phytoplankton are used to illustrate the many possible targets and effects of UVBR. The role of photosynthetically active radiation in causing dynamic and chronic photoinhibition in macroalgae and the interactions of PAR with UVR are examined in detail. These interactions are central to interpretation of field measurements of photoinhibition under natural solar radiation conditions. Potential strategies and mechanisms for repair of UVBR damage are discussed. Before the long-term effects of UVBR on macroalgal production and community structure can be determined, a greater knowledge of the specific targets of UVBR in macrophytes and the mechanisms of protection and repair must be determined. The ability of macrophytes to acclimate to higher UVBR and the interaction of UVBR with other stresses, such as high PAR, temperature and desiccation, must be assessed. Studies are needed which encompass effects on all stages of the macrophyte life cycle, from recruitment to maturity.

Review

Decreases in the concentration of ozone in the stratosphere are predicted to result in more biologically damaging ultraviolet-B radiation (UVBR) reaching the Earth's surface in the near future. The consequences for plant life of this small change in the solar spectrum are currently uncertain; this is particularly true for aquatic macrophytic algae. The aim of this review is to summarize the current knowledge of UVBR effects on macrophytes, and to highlight areas for future research. An overview of published underwater UVBR measurements shows that penetration of this waveband is low in the coastal waters where most macroalgae are found. Knowledge of UVBR targets in macroalgae is poor, and biological weighting functions have yet to be established. Studies of higher plants and phytoplankton are used to illustrate the many possible targets and effects of UVBR. The role of photosynthetically active radiation in causing dynamic and chronic photoinhibition in macroalgae and the interactions of PAR with UVR are examined in detail. These interactions are central to interpretation of field measurements of photoinhibition under natural solar radiation conditions. Potential strategies and mechanisms for repair of UVBR damage are discussed. Before the long-term effects of UVBR on macroalgal production and community structure can be determined, a greater knowledge of the specific targets of UVBR in macrophytes and the mechanisms of protection and repair must be determined. The ability of macrophytes to acclimate to higher UVBR and the interaction of UVBR with other stresses, such as high PAR, temperature and desiccation, must be assessed. Studies are needed which encompass effects on all stages of the macrophyte life cycle, from recruitment to maturity.

A garden study of the effects of ultraviolet-B radiation on pollination success and lifetime female fitness in Brassica.

While a large number of studies have examined the effects of increased ultraviolet-B radiation (UV-B) on growth and physiological function of plants, UV-B effects on pollination success and fitness are poorly understood. To examine this question, we measured growth, timing of flowering, pollination success, production of pollen, ovules, flowers, fruits, and seeds, and quality of offspring produced by Brassica nigra and B. rapa in a garden experiment. A total of 313 plants of the two species were randomly divided into two treatment groups. One group received only natural ambient levels of UV-B, while the other received an artificially enhanced UV-B dose. Fitness of B. nigra declined at the higher UV-B dose while B. rapa fitness did not change. One possible cause of this result was a shift in the relative attractiveness of the two species to pollinators: visitation to B. nigra declined at the high UV-B dose while B. rapa visitation increased.

Vitamin C Abrogates the Deleterious Effects of UVB Radiation on Cutaneous Immunity by a Mechanism That Does Not Depend on TNF-α

Acute low-dose treatment of murine skin with ultra violet B (UVB) light impairs induction of contact hypersensitivity (CH) to dinitrofluorobenzene (DNFB) in certain inbred strains of mice (termed UVB-susceptible), but not in others (termed UVB-resistant), and promotes tolerance. These deleterious effects of ultraviolet radiation (UVR) are mediated in part by TNF-alpha, which is released from UVR-exposed epidermal and dermal cells. Because UVR damage to skin has also been ascribed in part to the generation of reactive oxygen intermediates (ROIs) such as superoxide anion (O2-), hydrogen peroxide (H2O2), hydroxyl radical (OH-), and singlet oxygen ((1)O2), we investigated whether vitamin C (ascorbic acid), which can nullify ROIs, prevents the deleterious effects of UVR on the cutaneous immune system. We found that epicutaneous application of vitamin C (10% L-ascorbic acid solution) abrogated the deleterious effects of acute low-dose UVR on induction of CH and prevented the induction of tolerance. Vitamin C, however, did not reverse the effects of TNF-alpha on CH induction and tolerance. These results indicate that (i) ROIs generated intracutaneously by UVR contribute to the impaired ability of exposed skin to support the induction of CH and to promote the induction of tolerance and (ii) these effects are not dependent on TNF-alpha.