Ambient UV-B Levels Research Articles

Secondary metabolites and related genes in Vitis vinifera L. cv. Tempranillo grapes as influenced by ultraviolet radiation and berry development.

The effects of UV radiation on Vitis vinifera cv Tempranillo grapes were studied under field conditions as influenced by ultraviolet (UV) band (UV-A and UV-B), UV-B level (ambient vs enhanced), grape phenological stage (pea-size, veraison, and harvest), grape component (skin, flesh, and seeds), and fraction from which phenolic UV-absorbing compounds (UVACs) were extracted (soluble vs insoluble). Ambient UV-B levels caused stronger effects than ambient UV-A. These effects included increases in flavonol contents (particularly quercetins and kaempferols), the expression of flavonol synthase and chalcone synthase genes (VvFLS4 and VvCHS1), and grape weight and size. In addition, the contents of flavanols and hydroxycinnamic acids increased under UV-B radiation at pea-size stage. All these compounds play physiological roles as antioxidants and UV screens. Synergic effects between UV-B and UV-A were observed. The responses of anthocyanins, stilbenes, and volatile compounds to UV were diffuse or nonexistent. Enhanced UV-B led to rather subtle changes in comparison with ambient UV-B, but differences between both treatments could be demonstrated by multivariate analysis. Pea-size and harvest were the phenological stages where the most significant responses to UV were found, while the skin was the most UV-responsive grape component. Soluble phenolic compounds were much more UV-responsive than insoluble compounds. In conclusion, UV radiation was essential for the induction of specific grape phenolic and volatile compounds. Given the physiological roles of these compounds, as well as their contribution to grape and wine quality, and their potential use as nutraceuticals, our results may have implications on the artificial manipulation of UV radiation.

Investigating the Potential for Ultraviolet Light to Modulate Morbidity and Mortality From COVID-19: A Narrative Review and Update.

During the COVID-19 (coronavirus disease of 2019) pandemic, researchers have been seeking low-cost and accessible means of providing protection from its harms, particularly for at-risk individuals such as those with cardiovascular disease, diabetes and obesity. One possible way is via safe sun exposure, and/or dietary supplementation with induced beneficial mediators (e.g., vitamin D). In this narrative review, we provide rationale and updated evidence on the potential benefits and harms of sun exposure and ultraviolet (UV) light that may impact COVID-19. We review recent studies that provide new evidence for any benefits (or otherwise) of UV light, sun exposure, and the induced mediators, vitamin D and nitric oxide, and their potential to modulate morbidity and mortality induced by infection with SARS-CoV-2 (severe acute respiratory disease coronavirus-2). We identified substantial interest in this research area, with many commentaries and reviews already published; however, most of these have focused on vitamin D, with less consideration of UV light (or sun exposure) or other mediators such as nitric oxide. Data collected to-date suggest that ambient levels of both UVA and UVB may be beneficial for reducing severity or mortality due to COVID-19, with some inconsistent findings. Currently unresolved are the nature of the associations between blood 25-hydroxyvitamin D and COVID-19 measures, with more prospective data needed that better consider lifestyle factors, such as physical activity and personal sun exposure levels. Another short-coming has been a lack of measurement of sun exposure, and its potential to influence COVID-19 outcomes. We also discuss possible mechanisms by which sun exposure, UV light and induced mediators could affect COVID-19 morbidity and mortality, by focusing on likely effects on viral pathogenesis, immunity and inflammation, and potential cardiometabolic protective mechanisms. Finally, we explore potential issues including the impacts of exposure to high dose UV radiation on COVID-19 and vaccination, and effective and safe doses for vitamin D supplementation.

Differential investment in pre- and post-mating male sexual traits in response to prolonged exposure to ambient UVB radiation in a fish

Increasing UVB radiation (UVB) reaching earth's surface following stratospheric ozone depletion is linked to serious consequences for organisms. While studies have focused on direct cytocidal and immunomodulatory effects of UVB, indirect consequences for fitness-related life-history traits are largely unexplored, although knowledge is needed to understand organismal responses to climate change. The present study investigates the effects of developmental exposure to enhanced, but ecologically relevant, ambient UVB levels on growth (body size), parental behavior (nest-building), fitness-enhancing traits of pre-mating (sexual ornamentation) and post-mating (sperm traits) sexual selection as well as their interrelationships in male three-spined sticklebacks (Gasterosteus aculeatus). Moreover, potentially underlying direct UVB effects, testicular antioxidant capacity (TAC) and testes and skin melanization were quantified. Juvenile full-siblings were split into two groups and raised until adulthood in a semi-natural set-up under light conditions including either natural (UVBnormal) or elevated UVB levels (UVBenhanced). When becoming reproductive, males were kept individually before data collection took place at their reproductive peak. The results showed that males from the UVBenhanced-group were smaller than their brothers from the UVBnormal-treatment, whereas no treatment differences were observed for sexual ornamentation, sperm traits and TAC. Moreover, UVB-stressed males built their nests faster and the relationship between body size and nest size was negative for UVBenhanced-males while being positive for UVBnormal-males. These results demonstrate that, depending on physical state, UVB-stressed males adjusted their behavior to some extent. Additionally, a trade-off between the investment in pre- and post-mating traits was found for UVBenhanced-males, i.e. the intensity of their breeding coloration was negatively correlated with sperm number whereas this relationship was reversed for UVBnormal-males, thus showing an interaction between pre- and post-mating traits regarding exposure treatment. The interaction provides first experimental evidence that differential allocation to energetically demanding pre- and post-mating components of male fitness is triggered by a key environmental stressor of climate change.

Vitamin D status among the elderly Chinese population: a cross-sectional analysis of the 2010\u20132013 China national nutrition and health survey (CNNHS)

BackgroundVitamin D inadequacy is common among the elderly, especially within the Asian population. The vitamin D status among healthy adults in the elderly Chinese population was evaluated.MethodsA total of 6014 healthy adults aged 60 years or older (2948 men, 3066 women) participated in this descriptive cross-sectional analysis. Possible predictors of vitamin D inadequacy were evaluated via multiple logistic regression analyses.ResultsThe median serum 25-hydroxyvitamin D (25(OH)D) levels were 61.0 nmol/l (interquartile range (IQR) 44.3–80.6, range 5.1–154.5) for men and 53.7 nmol/l (IQR 38.8–71.0, range 6.0–190.0) for women, with 34.1% (95% confidence interval (CI) 32.4–35.8) of men and 44.0% (95% CI 42.2–45.8) of women presenting vitamin D inadequacy (25(OH)D <50 nmol/l). According to the multivariate logistic regression analyses, vitamin D inadequacy was positively correlated with female gender (P <0.0001), underweight (P = 0.0259), the spring season (P <0.0001), low ambient UVB levels (P <0.0001) and living in large cities (P = 0.0026). For men, vitamin D inadequacy was positively correlated with the spring season (P = 0.0015), low ambient UVB levels (P <0.0001) and living in large cities (P = 0.0022); for women, vitamin D inadequacy was positively correlated with the spring season (P = 0.0005) and low ambient UVB levels (P <.0001).ConclusionsVitamin D inadequacy is prevalent among the elderly population in China. Because residing in regions with low ambient UVB levels increases the risk of vitamin D inadequacy both for men and women, vitamin D supplementation and sensible sun exposure should be encouraged, especially during the cooler seasons. Further studies are required to determine the optimal vitamin D intake and sun exposure levels to maintain sufficient vitamin D levels in the elderly Chinese population.

Vitamin D deficiency prevalence and risk factors among pregnant Chinese women.

To evaluate vitamin D deficiency prevalence and risk factors among pregnant Chinese women. A descriptive cross-sectional analysis. China National Nutrition and Health Survey (CNNHS) 2010-2013. A total of 1985 healthy pregnant women participated. Possible predictors of vitamin D deficiency were evaluated via multiple logistic regression analyses. The median serum 25-hydroxyvitamin D level was 15·5 (interquartile range 11·9-20·0, range 3·0-51·5) ng/ml, with 74·9 (95 % CI 73·0, 76·7) % of participants being vitamin D deficient (25-hydroxyvitamin D <20 ng/ml). According to the multivariate logistic regression analyses, vitamin D deficiency was positively correlated with Hui ethnicity (P=0·016), lack of vitamin D supplement use (P=0·021) and low ambient UVB level (P<0·001). In the autumn months, vitamin D deficiency was related to Hui ethnicity (P=0·012) and low ambient UVB level (P<0·001). In the winter months, vitamin D deficiency was correlated with younger age (P=0·050), later gestational age (P=0·035), higher pre-pregnancy BMI (P=0·019), low ambient UVB level (P<0·001) and lack of vitamin D supplement use (P=0·007). Vitamin D deficiency is prevalent among pregnant Chinese women. Residing in areas with low ambient UVB levels increases the risk of vitamin D deficiency, especially for women experiencing advanced stages of gestation, for younger pregnant women and for women of Hui ethnicity; therefore, vitamin D supplementation and sensible sun exposure should be encouraged, especially in the winter months. Further studies must determine optimal vitamin D intake and sun exposure levels for maintaining sufficient vitamin D levels in pregnant Chinese women.

The relationship between UV-irradiance, photoprotective compounds and DNA damage in two intertidal invertebrates with contrasting mobility characteristics

The photoprotective role of mycosporine-like amino acids (MAA) against the generation of DNA cyclobutane pyrimidine dimers (CPD) was studied in the sessile intertidal anemone Actinia tenebrosa and the mobile intertidal gastropod Diloma aethiops through 27months at a mid-latitude New Zealand location. MAA were sequestered by A. tenebrosa and D. aethiops from their diet, although maximum total MAA levels in both species were not correlated with seasonal variation in maximum ambient UV-B levels recorded at the collection site. Temporal changes in total MAA in A. tenebrosa showed a six months lag-time in their concentration regarding to the environmental UV-B levels. This lag period corresponded to an observed increase in CPD production from spring to summer; suggesting that MAA do not completely protect the anemone from UV-B during summer. For D. aethiops, total MAA concentrations did not change significantly during the study, although qualitative changes in MAA were apparent. A month lag-time in MAA concentration in D. aethiops and possibly the physical barrier that the shell confers to the animal, can explain reduced CPD levels in comparative terms with A. tenebrosa. Although MAA are used by invertebrates for photoprotection, contrasting mobility characteristics and the presence of physical adaptations can confer them important protection levels during temporal changes of UV-B at mid-latitude places of the Southern Hemisphere.

Altitudinal and seasonal changes of phenolic compounds in Buxus sempervirens leaves and cuticles

The variation in the leaf content of phenolic compounds has been related to the UV-B changes of the environment in which plants grow. In this context, we aimed to investigate: a) whether the seasonal and altitudinal changes in the content of phenolic compounds of Buxus sempervirens L. leaves and cuticles could be related to the natural fluctuations in UV-B levels and b) the possible use of specific phenolic compounds as biomarkers of ambient UV-B levels. To achieve these goals we sampled, every three months during one year, leaves of B.sempervirens along an altitudinal gradient. At the lowest and the highest altitudes, we also conducted a UV-exclusion experiment to discern whether the observed changes could be attributed to the natural variation in UV-B. Results show that total phenolic content of leaves was lower in June than in the other sampling dates, which suggests a leaf ontogenic rather than a UV-B effect on the leaf content of these compounds. Regarding the elevational gradient, the overall amount of phenolic acids and neolignan of entire leaves increased with altitude while the total amount of flavonoids in leaf cuticles decreased. However, the lack of a significant effect of our UV-exclusion treatment on the content of these compounds suggests that the observed variations along the altitudinal gradient would respond to other factors rather than to UV-B. Concomitantly, we did not find any phenolic compound in leaves or cuticles of B.sempervirens that could be considered as a biomarker of ambient UV-B levels.

Validity and Use of the UV Index

The adequacy of the UV Index (UVI), a simple measure of ambient solar ultraviolet (UV) radiation, has been questioned on the basis of recent scientific data on the importance of vitamin D for human health, the mutagenic capacity of radiation in the UVA wavelength, and limitations in the behavioral impact of the UVI as a public awareness tool. A working group convened by ICNIRP and WHO met to assess whether modifications of the UVI were warranted and to discuss ways of improving its effectiveness as a guide to healthy sun-protective behavior. A UV Index greater than 3 was confirmed as indicating ambient UV levels at which harmful sun exposure and sunburns could occur and hence as the threshold for promoting preventive messages. There is currently insufficient evidence about the quantitative relationship of sun exposure, vitamin D, and human health to include vitamin D considerations in sun protection recommendations. The role of UVA in sunlight-induced dermal immunosuppression and DNA damage was acknowledged, but the contribution of UVA to skin carcinogenesis could not be quantified precisely. As ambient UVA and UVB levels mostly vary in parallel in real life situations, any minor modification of the UVI weighting function with respect to UVA-induced skin cancer would not be expected to have a significant impact on the UV Index. Though it has been shown that the UV Index can raise awareness of the risk of UV radiation to some extent, the UVI does not appear to change attitudes to sun protection or behavior in the way it is presently used. Changes in the UVI itself were not warranted based on these findings, but rather research testing health behavior models, including the roles of self-efficacy and self-affirmation in relation to intention to use sun protection among different susceptible groups, should be carried out to develop more successful strategies toward improving sun protection behavior.

Potassium ion fluxes in corneal epithelial cells exposed to UVB

The goal of this study was to investigate the efflux of K+ from human corneal limbal epithelial cells (HCLE) exposed to ambient levels of UVB, which is known to cause apoptosis, and to examine the effect of K+ channel blockers on loss of potassium induced by UVB. HCLE cells were exposed to 100–200 mJ/cm2 UVB, followed by incubation in culture media with 5.5–100 mM K+, BDS-1, Ba2+ or ouabain. To measure intracellular cations, cells were washed in 280 mM sucrose and lysed in DI water. K+ and Na+ levels in lysates were measured by ion chromatography. HCLE cells showed maximal loss of K+i 10 min after exposure to UVB and 5.5 mM K+ media, with recovery of normal K+ levels after 90 min. Treatment with 1 μM BDS-1 following UVB exposure reduced the loss of K+ by HCLE cells. Exposure to 0.1–5 mM Ba2+ inhibited UVB-induced K+ loss in a time and dose-dependent manner. These results confirm that blocking K+ channels in HCLE cells exposed to UVB prevents efflux of K+, confirming that UVB activates K+ channels in these cells. Electrophysiology data show that K+ channels remain highly active at least 90 min after UVB exposure. HCLE cells exposed to UVB and incubated in 0.01–1 μM ouabain did not recover from UVB-induced K+ loss. These data suggest that the Na/K pump may act to restore [K+]i to control levels in HCLE cells following UVB exposure and that the pump is not damaged by exposure to UVB. Incubation of HCLE cells exposed to UVB in medium with 25–100 mM K+ media prevented K+ efflux at extracellular concentrations as low as 25 mM (the concentration in tear fluid), maintaining control levels of K+i. In all experiments inward fluxes and intracellular Na+ levels mirrored K+ changes, albeit at the expected lower concentrations. The prevention of UVB-induced Ki+ loss by 25 mM Ko+ is consistent with the possible contribution of the relatively high K+ concentration in tears to protection of the corneal epithelium from ambient UVB.

Experimental examination of the effects of ultraviolet-B radiation in combination with other stressors on frog larvae

Ultraviolet-B radiation (UVB) is a ubiquitous stressor with negative effects on many aquatic organisms. In amphibians, ambient levels of UVB can result in impaired growth, slowed development, malformations, altered behavior and mortality. UVB can also interact with other environmental stressors to amplify these negative effects on individuals. In outdoor mesocosm and laboratory experiments we studied potential synergistic effects of UVB, a pathogenic fungus, Batrachochytrium dendrobatidis (Bd), and varying temperatures on larval Cascades frogs (Rana cascadae). First, we compared survivorship, growth and development in two mesocosm experiments with UVB- and Bd-exposure treatments. We then investigated the effects of UVB on larvae in the laboratory under two temperature regimes, monitoring survival and behavior. We found reduced survival of R. cascadae larvae with exposure to UVB radiation in all experiments. In the mesocosm experiments, growth and development were not affected in either treatment, and no effect of Bd was found. In the laboratory experiment, larvae exposed to UVB demonstrated decreased activity levels. We also found a trend towards reduced survival when UVB and cold temperatures were combined. Our results show that amphibian larvae can suffer both lethal and sublethal effects when exposed to UVB radiation.

Exposure to Increased Ambient Ultraviolet B Radiation has Negative Effects on Growth, Condition and Immune Function of Juvenile Atlantic Salmon (Salmo salar)

Atlantic salmon (Salmo salar) parr were exposed in two outdoor experiments, ranging in duration from 52 to 137 days, to spectral treatments: (1) natural sunlight (=present ambient UVB level), (2) solar radiation supplemented with enhanced UVB radiation from lamps simulating 20% or 8% stratospheric ozone loss or (3) UVB-depleted sunlight achieved by screening with Mylar-D film. The growth, condition and immune function of the salmon were quantified after treatments. Exposure to enhanced UVB radiation retarded growth, and decreased hematocrit value and plasma protein concentration. Further, enhanced UVB radiation affected plasma immunoglobulin concentration. The results demonstrate that juvenile Atlantic salmon are not able to fully adapt to increased ambient UVB levels in long-term exposures, and the interference with immune system function suggests a negative effect of UVB on disease resistance in Atlantic salmon.

Combined exposure to ambient UVB radiation and nitrite negatively affects survival of amphibian early life stages

Many aquatic species are sensitive to ambient levels of ultraviolet-B radiation (UVB) and chemical fertilizers. However, recent studies indicate that the interaction among multiple stressors acting simultaneously could be contributing to the population declines of some animal species. Therefore, we tested the potential synergistic effects between ambient levels of UVB and a contaminant, sodium nitrite in the larvae of two amphibian species, the common European toad Bufo bufo and the Iberian green frog Rana perezi. We studied R. perezi from both mountain and coastal populations to examine if populations of the same species varied in their response to stressors in different habitats. Both species were sensitive to the two stressors acting alone, but the interaction between the two stressors caused a multiplicative impact on tadpole survival. For B. bufo, the combination of UVB and nitrite was up to seven times more lethal than mortality for each stressor alone. In a coastal wetland, the combination of UVB and nitrite was four times more toxic for R. perezi than the sum of the effect on mortality for each stressor alone. One mg/L of nitrite killed half the population of R. perezi at Gredos Mountains at day 10 in the absence of UVB. In the presence of UVB, 50% of the tadpoles from the same experiment died at day 7. Similar toxic response were found for R. perezi in two highly contrasted environments suggesting this synergistic interaction can be a widespread phenomenon. The interaction of excess chemical fertilizers and manure with ambient UVB radiation could be contributing to the global decline of some amphibian species. We suggest that potential exposure to UVB radiation be accounted for when assessing water quality criteria regarding nitrite pollution.

Coupling Short‐Term Changes in Ambient UV‐B levels with Induction of UV‐Screening Compounds†

A substantial number of studies have been conducted over the last several decades to assess the potential impacts of long-term increases in ultraviolet-B radiation (UV-B between 280 and 320 nm) that will result from continued depletion of stratospheric ozone. However, seasonal changes, tropospheric chemistry and cloudiness are the dominant factors controlling ambient UV-B levels on a short-term or daily basis. The effects of short-term changes in UV-B on plant growth, phytochemistry and physiological processes have received relatively little attention. The USDA UV-B Monitoring and Research Program provides an excellent network of stations that provide an opportunity to monitor long-term changes in solar UV-B radiation and evaluate the responses of plants to short-term variation in UV-B levels on a near-real-time basis. In this study barley (Hordeum vulgare L.) and soybean (Glycine max [L] Merr.) were used as model systems. Emerging seedlings of these species were grown under either near-ambient levels of UV-B or under reduced levels (ca 90% reduction) in the field. Periodic measurements of foliar UV-screening compounds were made on separate groups of seedlings planted at intervals over the growing season during contrasting periods of ambient levels of UV radiation. The levels of UV-screening compounds correlated with UV-B levels in both species and with UV-A in soybean but the sensitivity of the response differed between the two species and among the soybean cultivars. Response differences among species may be related to unique secondary chemistry of each species, so one response estimate or action spectrum may not be appropriate for all species.

Variable phytoplankton response to enhanced UV-B and nitrate addition in mesocosm experiments at three latitudes (Canada, Brazil and Argentina)

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 313:57-72 (2006) - doi:10.3354/meps313057 Variable phytoplankton response to enhanced UV-B and nitrate addition in mesocosm experiments at three latitudes (Canada, Brazil and Argentina) Maria Lorena Longhi1,4, Gustavo Ferreyra1,2, Irene Schloss2,3, Suzanne Roy1,* 1Institut des Sciences de la Mer de Rimouski, Université du Québec à Rimouski, 310 Allée des Ursulines, Rimouski, Québec G5L 3A1, Canada 2Instituto Antártico Argentino, Cerrito 1248, C1010AAZ, Buenos Aires, Argentina 3Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina 4Present address: Faculté des Sciences, Université du Québec à Montréal, succ. Centre-Ville, C.P. 8888, Montréal, Québec H3C 3P8, Canada *Corresponding author. Email: suzanne_roy@uqar.qc.ca ABSTRACT: The influence of nitrate enrichment on the response of natural phytoplankton populations to enhanced UV-B radiation was tested during a series of week-long mesocosm (1800 l) experiments carried out in Rimouski (Canada), Ubatuba (Brazil) and Ushuaia (southern Argentina). We set up 2 mesocosms at each site, one was submitted to ambient UV-B levels while the other received enhanced UV-B levels corresponding to a local 60% ozone-depletion scenario, and both were continuously mixed. Samples from the mesocosms were incubated in UV-transparent plastic bags (4 l) floating at the surface for 24 h. Half of these received nitrate, phosphate and silicate enrichments while for the other half nitrate was omitted. Responses in terms of photochemical yield (Fv/Fm, where Fv is variable fluorescence after dark relaxation and Fm is maximal fluorescence following short pulses of saturating white light, pulse amplitude-modulated [PAM] fluorescence) and high-performance liquid chromatography (HPLC) pigments, differed among sites and over time, particularly for Rimouski, where a large bloom took place in the mesocosms. Enhanced UV-B significantly increased photoinhibition in the surface bags, while nitrate addition partly relieved this inhibition only during the post-bloom period. The net growth of fucoxanthin was reduced by enhanced UV-B except during the post-bloom period, when it increased, probably because grazing pressure was reduced under enhanced UV-B (strong decrease in ciliates). In Ubatuba, cells were affected by the high ambient-light irradiances at the surface, and enhanced UV-B had no further effect, irrespective of the nutrient status. At Ushuaia, enhanced UV-B prevented all increases of fucoxanthin and chl a, with much less effect on chl b (green algae), and no nutrient response was observed. This strong and consistent negative response to enhanced UV-B is likely to be related to the cold temperature prevailing at Ushuaia at the time of the experiment (slowing repair) as well as the local community composition. In contrast, no effects of enhanced UV-B were observed in the stirred mesocosms at the 3 sites, indicating that mixing moderated the UV-B effects in all 3 experiments. KEY WORDS: UV-B radiation · Nutrient status · Phytoplankton · Fv/Fm · Pigments · Latitudinal variations · Nitrate availability Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 313. Online publication date: May 11, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Outdoor Studies on the Effects of Solar UV-B on bryophytes: Overview and Methodology

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

Radiation-Induced in Vitro Phototoxic Potential of Some Fluoroquinolones

Photosensitizing drugs that can damage cellular biomolecules is a matter of concern. Lomefloxacin, norfloxacin, ofloxacin, and enoxacin (broad-spectrum antibiotics of fluoroquinolone group) are used for the treatment of Gram-positive and Gram-negative bacterial infections. Phototoxicity and possible mechanism of their action was assessed under the exposure of ambient levels of UV-A, UV-B, and sunlight at a concentration generally used in the treatment of various diseases. Singlet oxygen (1O2), superoxide anion radical (O2·−) generation, DNA damage, and lipid peroxidation in human blood were studied. All the fluoroquinolones tested in this study produced 1O2 and O2·− under exposure to UV-A, UV-B, and sunlight depending on the concentrations (0 to 60 μg/mL) of the drugs. Enoxacin showed a higher yield of 1O2 and O2·− than other drugs. These materials also degraded deoxyguanosine and induced lipid peroxidation in vitro under exposure to UV-A, UV-B, and sunlight (depending on the dose of radiation). The formation of the reactive oxygen species (ROS) by the photoexcited drugs may be considered as a possible mechanism of their action.

The effects of UV-B, nitrogen fertilization, and springtime warming on sugar maple seedlings and the soil chemistry of two central Ontario forests

The interactive effects of springtime warming, ambient UV-B, and nitrogen fertilization on the chemistry of sugar maple (Acer saccharum Marsh.) seedlings and soils from two contrasting sites were assessed. Open-top chambers increased average springtime air temperatures by approximately 1.5 °C, but their heating effect was diminished upon closure of the overstory canopy. Ambient levels of UV-B were reduced with Mylar D polyester film. Ammonium nitrate fertilizer was added in an amount equivalent to an additional 50 kg N·ha–1. The soils of the Oliver forest were deep luvisols overlying a strongly calcareous till (average pH 6.0), while the naturally acidic soils of Haliburton were derived from the Precambrian Shield (average pH 4.7). Of the three main treatments used in this study, application of nitrogen fertilizer had the greatest impacts on foliar chemistry. At both sites, fertilizer application increased the acidity of the soils, while at Haliburton there were losses in total soil calcium. Haliburton maple seedlings had increased foliar concentrations of aluminum and manganese, decreased concentrations of calcium, and reduced calcium/manganese and magnesium/manganese nutrient ratios, after fertilizer was applied. Meanwhile, seedlings growing on the more alkaline soils of Oliver had increased foliar concentrations of magnesium following application of the nitrogen fertilizer. We suggest that these changes in the elemental chemistry of the soils and foliage brought on by continued nitrogen loading may predispose seedlings growing on naturally acidic soils, such as those of the Precambrian Shield, to further stress from additional abiotic and biotic stressors.

Depletion of stratospheric ozone over the Antarctic and Arctic: Responses of plants of polar terrestrial ecosystems to enhanced UV-B, an overview

Depletion of stratospheric ozone over the Antarctic has been re-occurring yearly since 1974, leading to enhanced UV-B radiation. Arctic ozone depletion has been observed since 1990. Ozone recovery has been predicted by 2050, but no signs of recovery occur. Here we review responses of polar plants to experimentally varied UV-B through supplementation or exclusion. In supplementation studies comparing ambient and above ambient UV-B, no effect on growth occurred. UV-B-induced DNA damage, as measured in polar bryophytes, is repaired overnight by photoreactivation. With UV exclusion, growth at near ambient may be less than at below ambient UV-B levels, which relates to the UV response curve of polar plants. UV-B screening foils also alter PAR, humidity, and temperature and interactions of UV with environmental factors may occur. Plant phenolics induced by solar UV-B, as in pollen, spores and lignin, may serve as a climate proxy for past UV. Since the Antarctic and Arctic terrestrial ecosystems differ essentially, (e.g. higher species diversity and more trophic interactions in the Arctic), generalization of polar plant responses to UV-B needs caution.

Effects of ultraviolet-B radiation on cotton (Gossypium hirsutum L.) morphology and anatomy.

Cotton (Gossypium hirsutum L.) crop, cultivated between 40 degrees N and 40 degrees S, is currently experiencing 2-11 kJ m-2 d-1 of UV-B radiation. This is predicted to increase in the near future. An experiment was conducted to study the effect of enhanced UV-B radiation on vegetative and reproductive morphology and leaf anatomy of cotton in sunlit, controlled environment chambers. From emergence to harvest, cotton plants were exposed to 0, 8 or 16 kJ m-2 d-1 of UV-B in a square wave approach for 8 h from 0800 to 1600 h. Changes in plant height, internode and branch length, mainstem node number, leaf area, length and area of petals and bracts, and anther number per flower were recorded. Epidermal cell and stomatal density, stomatal index, leaf thickness, and epidermal, palisade and mesophyll tissue thickness were also measured. Initial chlorotic symptoms on leaves turned into necrotic patches on continued exposure to enhanced UV-B. Exposure to high UV-B reduced both vegetative and reproductive parameters and resulted in a smaller canopy indicating sensitivity of cotton to UV-B radiation. Enhanced UV-B radiation increased epicuticular wax content on adaxial leaf surfaces, and stomatal index on both adaxial and abaxial leaf surfaces. Leaf thickness was reduced following exposure to UV-B owing to a decrease in thickness of both the palisade and mesophyll tissue, while the epidermal thickness remained unchanged. The vegetative parameters studied were affected only by high levels of UV-B (16 kJ m-2 d-1), whereas the reproductive parameters were reduced at both ambient (8 kJ m-2 d-1) and high UV-B levels. The study shows that cotton plants are sensitive to UV-B at both the whole plant and anatomical level.

Effects of UVB preconditioning on heat tolerance of cucumber ( Cucumis sativus L.)

To study the preconditioning effects of exposure to UVB on heat tolerance (44–48 °C), 10-day-old cucumber ( Cucumis sativus L.) seedlings were irradiated for 6 days with a daily dose of either 3.4, 5.5 or 10.6 kJ m −2 of biologically effective UVB (UVB BE). Cellulose diacetate-filtered UVB lamps were used to supply UVB. These approximated low, ambient (medium) and twice-ambient (high) UVB doses, respectively, at 42°N latitude on a clear day during the summer solstice. A parallel group of control plants, held under polyester (PE)-filtered UVB lamps, received no UVB. UVB treatment increased the level of methanol-extractable UV-absorbing phenols in cotyledons and primary leaves. In a further HPLC analysis of acid-hydrolyzed leaf extract, eight peaks were separated. The two major peaks were co-chromatographed with authentic flavonoids, quercetin and kaempferol. The quercetin-like compound was preferentially enhanced in UVB-exposed plants. When the low and medium UVB-irradiated plants were later heat-stressed (46 °C, 1 h), survival improved by 112 and 82% and height growth increased by 35 and 40%, respectively, compared with controls that received no UVB. In contrast to low and ambient levels of UVB, which reduced membrane leakage, twice-ambient levels increased lipid peroxidation and electrolyte leakage. Although exposure to above-ambient levels of UVB was injurious, low and ambient doses of UVB promoted survival and growth of cucumber seedlings. Such a synergism between UVB and heat tolerance could be used to precondition seedlings grown in UVB-deficient greenhouses and may benefit plants under the predicted global warming scenario.