Field testing of UV biological spectral weighting functions for higher plants

In biological research on the ozone depletion issue, action spectra are typically used as biological spectral weighting functions (BSWF). There has been little testing, however, of the appropriateness of different functions under realistic field conditions. Here we quantitatively evaluate a new BSWF for plant growth response to UV radiation, and other action spectra potentially usable as BSWF, in two seasons of field experiments. We utilized supplemental UV-B radiation with various combinations of filtered solar UV-A radiation. Our new BSWF, which we call the UV plant growth weighting function, indicates responses in the UV-A waveband. In field tests it proved to be the most appropriate weighting function for the responses we measured in oat ( Avena sativa L. cv. Otana) over the two field seasons in these studies. A 10-day field experiment with canola, Brassica rapa L. cv. Goldrush , also suggested substantial effects of both UV-B and UV-A radiation on growth. If this new UV plant growth BSWF proves to be appropriate for many plant species, it represents a lower radiation amplification factor (RAF) than several previously used weighting functions for plants. This means less change in biologically effective UV for each increment of ozone column change. However, the lower RAF also means that experiments utilizing supplemental UV treatments have supplied milder doses of additional UV than intended, since they were based on BSWF that overemphasized UV-B and ignored the UV-A region. While we await continued field testing of BSWF on diverse taxa, we recommend: (1) reporting weighted irradiance with our new BSWF, and other appropriate functions; (2) continued reporting of the generalized plant weighted UV for continuity and comparative purposes, since it has been so widely used.     

Solar UV-B Radiation Inhibits the Growth of Antarctic Terrestrial Fungi

We tested the effects of solar radiation, and UV-B in particular, on the growth of Antarctic terrestrial fungi. The growth responses to solar radiation of five fungi, Geomyces pannorum, Phoma herbarum, Pythium sp., Verticillium sp., and Mortierella parvispora, each isolated from Antarctic terrestrial habitats, were examined on an agar medium in the natural Antarctic environment. A 3-h exposure to solar radiation of >287 nm reduced the hyphal extension rates of all species relative to controls kept in the dark. Pythium sp. cultures exposed to solar radiation for 1.5 h on five consecutive days were most sensitive to radiation of >287 nm, but radiation of >313 nm also inhibited growth to a lesser extent. Radiation of >400 nm had no effect on hyphal growth relative to controls kept in the dark. Short-wave solar UV-B radiation of between 287 and 305 nm inhibited the growth of Pythium sp. hyphae on and below the surface of the agar medium after 24 h, but radiation of ≥345 nm only reduced the growth of surface hyphae. Similar detrimental effects of UV-B on surface and, to a lesser extent, submerged hyphae of all five fungi were shown in the laboratory by using artificial UV-B from fluorescent lamps. A comparison of growth responses to solar radiation and temperature showed that the species that were most resistant to UV radiation grew fastest at higher temperatures. These data suggest that solar UV-B reduces the growth of fungi on the soil surface in the Antarctic terrestrial environment.     

Interactive Effects of Temperature and UV Radiation on Photosynthesis of Chlorella Strains from Polar,Temperate and Tropical Environments: Differential Impacts on Damage and Repair

Global warming and ozone depletion, and the resulting increase of ultraviolet radiation (UVR), have far-reaching impacts on biota, especially affecting the algae that form the basis of the food webs in aquatic ecosystems. The aim of the present study was to investigate the interactive effects of temperature and UVR by comparing the photosynthetic responses of similar taxa of Chlorella from Antarctic (Chlorella UMACC 237), temperate (Chlorella vulgaris UMACC 248) and tropical (Chlorella vulgaris UMACC 001) environments. The cultures were exposed to three different treatments: photosynthetically active radiation (PAR; 400–700 nm), PAR plus ultraviolet-A (320–400 nm) radiation (PAR + UV-A) and PAR plus UV-A and ultraviolet-B (280–320 nm) radiation (PAR + UV-A + UV-B) for one hour in incubators set at different temperatures. The Antarctic Chlorella was exposed to 4, 14 and 20°C. The temperate Chlorella was exposed to 11, 18 and 25°C while the tropical Chlorella was exposed to 24, 28 and 30°C. A pulse-amplitude modulated (PAM) fluorometer was used to assess the photosynthetic response of microalgae. Parameters such as the photoadaptive index (E_k) and light harvesting efficiency (α) were determined from rapid light curves. The damage (k) and repair (r) rates were calculated from the decrease in ΦPSII_eff over time during exposure response curves where cells were exposed to the various combinations of PAR and UVR, and fitting the data to the Kok model. The results showed that UV-A caused much lower inhibition than UV-B in photosynthesis in all Chlorella isolates. The three isolates of Chlorella from different regions showed different trends in their photosynthesis responses under the combined effects of UVR (PAR + UV-A + UV-B) and temperature. In accordance with the noted strain-specific characteristics, we can conclude that the repair (r) mechanisms at higher temperatures were not sufficient to overcome damage caused by UVR in the Antarctic Chlorella strain, suggesting negative effects of global climate change on microalgae inhabiting (circum-) polar regions. For temperate and tropical strains of Chlorella, damage from UVR was independent of temperature but the repair constant increased with increasing temperature, implying an improved ability of these strains to recover from UVR stress under global warming.     

Artificial and Solar UV Radiation Induces Strand Breaks and Cyclobutane Pyrimidine Dimers in Bacillus subtilis Spore DNA

The loss of stratospheric ozone and the accompanying increase in solar UV flux have led to concerns regarding decreases in global microbial productivity. Central to understanding this process is determining the types and amounts of DNA damage in microbes caused by solar UV irradiation. While UV irradiation of dormant Bacillus subtilis endospores results mainly in formation of the “spore photoproduct” 5-thyminyl-5,6-dihydrothymine, genetic evidence indicates that an additional DNA photoproduct(s) may be formed in spores exposed to solar UV-B and UV-A radiation (Y. Xue and W. L. Nicholson, Appl. Environ. Microbiol. 62:2221–2227, 1996). We examined the occurrence of double-strand breaks, single-strand breaks, cyclobutane pyrimidine dimers, and apurinic-apyrimidinic sites in spore DNA under several UV irradiation conditions by using enzymatic probes and neutral or alkaline agarose gel electrophoresis. DNA from spores irradiated with artificial 254-nm UV-C radiation accumulated single-strand breaks, double-strand breaks, and cyclobutane pyrimidine dimers, while DNA from spores exposed to artificial UV-B radiation (wavelengths, 290 to 310 nm) accumulated only cyclobutane pyrimidine dimers. DNA from spores exposed to full-spectrum sunlight (UV-B and UV-A radiation) accumulated single-strand breaks, double-strand breaks, and cyclobutane pyrimidine dimers, whereas DNA from spores exposed to sunlight from which the UV-B component had been removed with a filter (“UV-A sunlight”) accumulated only single-strand breaks and double-strand breaks. Apurinic-apyrimidinic sites were not detected in spore DNA under any of the irradiation conditions used. Our data indicate that there is a complex spectrum of UV photoproducts in DNA of bacterial spores exposed to solar UV irradiation in the environment.     

Consequences of depletion of stratospheric ozone for terrestrial Antarctic ecosystems: the response of Deschampsia antarctica to enhanced UV-B radiation in a controlled environment

Mini UV lamps were installed over antarctic plants at Léonie Island, Antarctic peninsula, and shoot length measurements of Deschampsia antarctica were performed during the austral summer January–February 1999.We studied the response of the antarctic hairgrass, Deschampsia antarctica to enhanced UV-B. In a climate room experiment we exposed tillers of Deschampsia antarctica, collected at Léonie Island, Antarctic peninsula, to ambient and enhanced levels of UV-B radiation. In this climate room experiment with 0, 2.5 and 5 kJ m^–2 day^–1 UV-B_BE treatments we observed that length growth of shoots at 2.5 and 5 kJ m^–2 day^–1 UV-B_BE was markedly reduced compared to 0 kJ m^–2 day^–1 UV-B_BE. In addition, there was an increased number of shoots and increased leaf thickness with enhanced UV-B. The Relative Growth Rate (RGR) was not affected by UV-B, possibly because reduced shoot length growth by enhanced UV-B was compensated by increased tillering. Light response curves of net leaf photosynthesis of plants exposed to 5 kJ m^–2 day^–1 UV-B_BE did not differ from those exposed to 0 kJ m^–2 day^–1 UV-B_BE. The content of UV-B absorbing compounds of plants exposed to increasing UV-B did not significantly change.Mini UV-B lamp systems were installed in the field, to expose the terrestrial antarctic vegetation at Léonie Island to enhanced solar UV-B. In that study, the increment of shoot length of tagged plants of Deschampsia antarctica during the January-February 1999 at Léonie Island, was recorded and compared to shoot length growth under controlled conditions.The consequences of enhanced UV-B radiation as a result of ozone depletion for the terrestrial antarctic ecosytems are discussed.     

Role of Dipicolinic Acid in Survival of Bacillus subtilis Spores Exposed to Artificial and Solar UV Radiation

Pyridine-2,6-dicarboxylic acid (dipicolinic acid [DPA]) constitutes approximately 10% of Bacillus subtilis spore dry weight and has been shown to play a significant role in the survival of B. subtilis spores exposed to wet heat and to 254-nm UV radiation in the laboratory. However, to date, no work has addressed the importance of DPA in the survival of spores exposed to environmentally relevant solar UV radiation. Air-dried films of spores containing DPA or lacking DPA due to a null mutation in the DPA synthetase operon dpaAB were assayed for their resistance to UV-C (254 nm), UV-B (290 to 320 nm), full-spectrum sunlight (290 to 400 nm), and sunlight from which the UV-B portion was filtered (325 to 400 nm). In all cases, air-dried DPA-less spores were significantly more UV sensitive than their isogenic DPA-containing counterparts. However, the degree of difference in UV resistance between the two strains was wavelength dependent, being greatest in response to radiation in the UV-B portion of the spectrum. In addition, the inactivation responses of DPA-containing and DPA-less spores also depended strongly upon whether spores were exposed to UV as air-dried films or in aqueous suspension. Spores lacking the gerA, gerB, and gerK nutrient germination pathways, and which therefore rely on chemical triggering of germination by the calcium chelate of DPA (Ca-DPA), were also more UV sensitive than wild-type spores to all wavelengths tested, suggesting that the Ca-DPA-mediated spore germination pathway may consist of a UV-sensitive component or components.     

Changes in biologically-active ultraviolet radiation reaching the Earth's surface.

The Montreal Protocol is working. Concentrations of major ozone-depleting substances in the atmosphere are now decreasing, and the decline in total column amounts seen in the 1980s and 1990s at mid-latitudes has not continued. In polar regions, there is much greater natural variability. Each spring, large ozone holes continue to occur in Antarctica and less severe regions of depleted ozone continue to occur in the Arctic. There is evidence that some of these changes are driven by changes in atmospheric circulation rather than being solely attributable to reductions in ozone-depleting substances, which may indicate a linkage to climate change. Global ozone is still lower than in the 1970s and a return to that state is not expected for several decades. As changes in ozone impinge directly on UV radiation, elevated UV radiation due to reduced ozone is expected to continue over that period. Long-term changes in UV-B due to ozone depletion are difficult to verify through direct measurement, but there is strong evidence that UV-B irradiance increased over the period of ozone depletion. At unpolluted sites in the southern hemisphere, there is some evidence that UV-B irradiance has diminished since the late 1990s. The availability and temporal extent of UV data have improved, and we are now able to evaluate the changes in recent times compared with those estimated since the late 1920s, when ozone measurements first became available. The increases in UV-B irradiance over the latter part of the 20th century have been larger than the natural variability. There is increased evidence that aerosols have a larger effect on surface UV-B radiation than previously thought. At some sites in the Northern Hemisphere, UV-B irradiance may continue to increase because of continuing reductions in aerosol extinctions since the 1990s. Interactions between ozone depletion and climate change are complex and can be mediated through changes in chemistry, radiation, and atmospheric circulation patterns. The changes can be in both directions: ozone changes can affect climate, and climate change can affect ozone. The observational evidence suggests that stratospheric ozone (and therefore UV-B) has responded relatively quickly to changes in ozone-depleting substances, implying that climate interactions have not delayed this process. Model calculations predict that at mid-latitudes a return of ozone to pre-1980 levels is expected by the mid 21st century. However, it may take a decade or two longer in polar regions. Climate change can also affect UV radiation through changes in cloudiness and albedo, without involving ozone and since temperature changes over the 21st century are likely to be about 5 times greater than in the past century. This is likely to have significant effects on future cloud, aerosol and surface reflectivity. Consequently, unless strong mitigation measures are undertaken with respect to climate change, profound effects on the biosphere and on the solar UV radiation received at the Earth's surface can be anticipated. The future remains uncertain. Ozone is expected to increase slowly over the decades ahead, but it is not known whether ozone will return to higher levels, or lower levels, than those present prior to the onset of ozone depletion in the 1970s. There is even greater uncertainty about future UV radiation, since it will be additionally influenced by changes in aerosols and clouds.     

Growth and reproduction of Antarctic vascular plants in response to warming and UV radiation reductions in the field

Along the west coast of the Antarctic Peninsula springtime ozone depletion events can lead to a two-fold increase in biologically effective UV-B radiation (UV-B_BE) and summer air temperatures have risen ≈1.5°C during the past 50 years. We manipulated levels of UV radiation and temperature around Colobanthus quitensis (a cushion-forming plant, Caryophyllaceae) and Deschampsia antarctica (a tussock grass) along the Peninsula near Palmer Station for two field seasons. Ambient levels of UV were manipulated by placing filters that either transmitted UV (filter control), absorbed UV-B (reducing diurnal levels of UV-B_BE by about 82%), or absorbed both UV-B and UV-A (reducing UV-B_BE and UV-A_BE by about 88 and 78%, respectively) on frames over naturally growing plants from November to March. Half the filters of each material completely surrounded the frames and raised diurnal and diel air temperatures around plants by an average of 2.3°C and 1.3°C, respectively. Reducing UV or warming had no effect on leaf concentrations of soluble UV-B absorbing compounds, UV-B absorbing surface waxes or chlorophylls. Warming had few effects on growth of either species over the first season. However, over the second field season warming improved growth of C. quitensis, leading to a 50% increase in leaf production (P < 0.10), a 26% increase in shoot production, and a 6% increase in foliar cover. In contrast, warming reduced growth of D. antarctica, leading to a 20% decline in leaf length, a 17% decline in leaf production (P < 0.10), and a 5% decline in foliar cover. Warming improved sexual reproduction in both species, primarily through faster development of reproductive structures and greater production of heavier seeds. Over the second field season, the percentage of reproductive structures that had reached the most developed (seed) stage in C. quitensis and D. antarctica was 20% and 15% higher, respectively, under warming. Capsules of C. quitensis produced 45% more seeds under warming and these seeds were 11% heavier. Growth of D. antarctica was improved when UV was reduced and these effects appeared to be cumulative over field seasons. Over the second season, tillers produced 55% more leaves and these leaves were 32% longer when UV-B was reduced. Tillers produced 137% more leaves that were 67% longer when both UV-B and UV-A were reduced. The effects of UV reduction were not as pronounced on C. quitensis, although over the second season cushions tended to be 17% larger and produce 21% more branches when UV-B was reduced, and tended to be 27% larger and produce 38% more branches when both UV-B and UV-A were reduced (P < 0.10). Few interactions were found between UV reduction and warming, although in the absence of warming, reducing UV led to slower development of reproductive structures in both species. The effects of warming and UV reduction were species specific and were often cumulative over the two field seasons, emphasizing the importance of long-term field manipulations in predicting the impacts of climate change. Received: 4 August 1998 / Accepted: 1 December 1998     

Effect of UV-B radiation on the growth and antioxidant enzymes of Antarctic sea ice microalgae <Emphasis Type="Italic">Chlamydomonas</Emphasis> sp. ICE-L

The effect of ultraviolet-B (UV-B) radiation on Antarctic phytoplankton has become an attractive ecological issue as a result of annual springtime ozone depletion. The effects of UV-B radiation on the growth and antioxidant enzymes were investigated using Antarctic sea ice microalgae Chlamydomonas sp. ICE-L as the material in this study. The results demonstrated that UV-B radiation could notably inhibit the growth, especially at high UV-B radiation intensity (70 μW cm⁻²). Malondialdehyde and O₂ ^·− content in ICE-L increased rapidly in early days (1–3 days) exposed to UV-B radiation enhancement, then decreased rapidly. In the stress of UV-B radiation enhancement, the superoxide dismutase, peroxidase and Catalase activities of 1–4 days in ICE-L were obviously higher than those in the control, and their activities became higher at high UV-B radiation intensity (70 μW cm⁻²). These enzymes activity of 7 days would kept stable at low UV-B radiation intensity (35 μW cm⁻²), but kept high level at high UV-B radiation intensity (70 μW cm⁻²). However, the ascorbate peroxidase activity in ICE-L kept stable under the stress of UV-B radiation enhancement. The above experimental results indicated that the antioxidant enzyme system played an important role in the adaptation of Antarctic ice microalgae under the UV-B radiation change of Antarctic ecosystems.     

UV radiation biomonitoring using cell compartmentation of UV-absorbing compounds in herbarium samples of a liverwort

Ultraviolet-absorbing compounds (UVACs) were analyzed in 90 herbarium samples of the liverwort Jungermannia exsertifolia subsp. cordifolia collected throughout Spain in the period 1913–2006, in order to evaluate their usefulness in UV radiation biomonitoring. This was assessed, for the first time in bryophytes, differentiating the soluble (mainly vacuolar) and insoluble (cell wall-bound) UVACs (respectively, SUVACs and IUVACs), which may represent different mechanisms to cope with UV radiation. The bulk levels of SUVACs and IUVACs, and the concentrations of seven individual compounds (five SUVACs and two IUVACs) were analyzed, and several environmental variables of the sampling points were obtained: longitude, latitude, altitude, ozone column, and modelled UV levels.Diverse positive relationships of UVAC variables with UV radiation levels were identified in both the temporal and spatial scales. The soluble compound p-coumaroylmalic acid showed significantly higher concentrations in the years after the onset of stratospheric ozone degradation (around 1975) with respect to the previous years. The bulk level and the concentrations of three individual SUVACs were higher in the Spanish samples analyzed in the present study than in the northern European samples analyzed in a previous study in which IUVACs were not considered. The bulk level of IUVACs was the biological variable best spatially correlated with the UV exposure of the samples and with important factors determining it, such as altitude and latitude. Furthermore, the bulk level of IUVACs was the biological variable selected by a stepwise multiple linear regression analysis to reconstruct the past levels of UV-B radiation. The reconstructed UV-B did not show a clear trend in the period 1913–2006, which was coincident with other climatic and biological UV reconstructions. Both SUVACs and IUVACs were significant loading factors differentiating summer and autumn samples in the Principal Components Analysis conducted using both UVACs and the environmental variables, but again the bulk level of IUVACs was the main loading factor differentiating the samples collected from the highest and most UV-exposed localities (Sierra Nevada). In general, these findings suggest that UVACs were stimulated by increased UV levels in time or space, and that IUVACs would be better UV protectants than SUVACs, probably due to their more efficient screening capacity.Overall, UVACs of J. exsertifolia subsp. cordifolia were good UV biomarkers, and their location in the soluble or cell wall-bound fractions determined their usefulness in the different aspects of UV biomonitoring, including the assessment of the UV-B increase associated to anthropogenic ozone degradation.     

Morphological and physiological responses of bean plants to supplemental UV radiation in a Mediterranean climate

During the last few decades many experiments have been performed to evaluate the responses of plants to enhanced solar UV-B radiation (280–320 nm) that may occur because of stratospheric ozone depletion; most of them were performed in controlled environment conditions where plants were exposed to low photosynthetically active radiation (PAR) levels and high UV-B irradiance. Since environmental radiative regimes can play a role in the response of plants to UV-B enhancement, it appears doubtful whether it is valid to extrapolate the results from these experiments to plants grown in natural conditions. The objective of this work was to evaluate the effects on physiology and morphology of a bean (Phaseolus vulgaris L.) cultivar Nano Bobis, exposed to supplemental UV radiation in the open-air. UV-B radiation was supplied by fluorescent lamps to simulate a 20% stratospheric ozone reduction. Three groups of plants were grown: control (no supplemental UV), UV-A treatment (supplementation in the UV-A band) and UV-B treatment (supplemental UV-B and UV-A radiation). Each group was replicated three times. After 33 days of treatment plants grown under UV-B treatment had lower biomass, leaf area and reduced leaf elongation compared to UV-A treatment. No significant differences were detected in photosynthetic parameters, photosynthetic pigments and UV-B absorbing compounds among the three groups of plants. However, plants exposed to UV-A treatment showed a sort of 'stimulation' of their growth when compared to the control. The results of this experiment showed that plants may be sensitive to UV-A radiation, thus it is difficult to evaluate the specific effects of UV-B (280–320 nm) radiation from fluorescent lamps and it is important to choose the appropriate control. Environmental conditions strongly affect plant response to UV radiation so further field studies are necessary to assess the interaction between UV-B exposure and meteorological variability.     

Synthesis,Structure and Antibacterial Activity of Potent DNA Gyrase Inhibitors: N′-Benzoyl-3-(4-Bromophenyl)-1H-Pyrazole-5-Carbohydrazide Derivatives

A total of 19 novel (3a–3s) N′-benzoyl-3-(4-bromophenyl)-1H-pyrazole-5-carbohydrazide analogs were designed, synthesized, and evaluated for biological activities as potential DNA gyrase inhibitors. The results showed that compound 3k can strongly inhibit Staphylococcus aureus DNA gyrase and Bacillus subtilis DNA gyrase (with IC₅₀ of 0.15 µg/mL and 0.25 µg/mL, respectively). Structure-activity relationships were also discussed base on the biological and docking simulation results.     

Beneficial effects of enhanced UV-B radiation under field conditions: improvement of needle water relations and survival capacity of Pinus pinea L. seedlings during the dry Mediterranean summer

The possible mechanism(s) by which supplemental UV-B radiation alleviates the adverse effects of summer drought in Mediterranean pines (Petropoulou et al. 1995) were investigated with seedlings of Pinus pinea. Plants received ambient or ambient plus supplemental UV-B radiation (biologically equivalent to a 15% ozone depletion over Patras, 38.3° N, 29.1° E) and natural precipitation or additional irrigation. Treatments started on 1 February, 1994 and lasted up to the end of the dry period (29 September). In well-watered plants, UV-B radiation had no influence on photosystem II photochemical efficiency and biomass accumulation. Water stressed plants suffered from needle loss and reduced photosystem II photochemical efficiency during the summer. These symptoms, however, were less pronounced in plants receiving supplemental UV-B radiation, resulting in higher total biomass at plant harvest. Laboratory tests showed that enhanced UV-B radiation did not improve the tolerance of photosystem II against drought, high light, high temperature and oxidative stress. Enhanced UV-B radiation, however, improved the water economy of water stressed plants, as judged by measurements of needle relative water content. In addition, it caused an almost two-fold increase of cuticle thickness. No such UV-B radiation effects were observed in well-watered pines. The results indicate that the combination of water stress and UV-B radiation may trigger specific responses, enabling the plants to avoid excessive water loss and, thereby, maintain a more efficient photosynthetic apparatus during the summer. The extent of this apparently positive UV-B radiation effect would depend on the amount of summer precipitation. Abbreviations: DW – dry weight, F_v/F_m – ratio of variable to maximum fluorescence, A ₃₀₀ – absorbance at 300 nm, PAR – photosynthetically active radiation, PS II – photosystem II, RWC – relative water content, TCA – trichloroacetic acid, UV-B_BE – biologically effective ultraviolet-B radiation     

High Mortality of Red Sea Zooplankton under Ambient Solar Radiation

High solar radiation along with extreme transparency leads to high penetration of solar radiation in the Red Sea, potentially harmful to biota inhabiting the upper water column, including zooplankton. Here we show, based on experimental assessments of solar radiation dose-mortality curves on eight common taxa, the mortality of zooplankton in the oligotrophic waters of the Red Sea to increase steeply with ambient levels of solar radiation in the Red Sea. Responses curves linking solar radiation doses with zooplankton mortality were evaluated by exposing organisms, enclosed in quartz bottles, allowing all the wavelengths of solar radiation to penetrate, to five different levels of ambient solar radiation (100%, 21.6%, 7.2%, 3.2% and 0% of solar radiation). The maximum mortality rates under ambient solar radiation levels averaged (±standard error of the mean, SEM) 18.4±5.8% h⁻¹, five-fold greater than the average mortality in the dark for the eight taxa tested. The UV-B radiation required for mortality rates to reach ½of maximum values averaged (±SEM) 12±5.6 h⁻¹% of incident UVB radiation, equivalent to the UV-B dose at 19.2±2.7 m depth in open coastal Red Sea waters. These results confirm that Red Sea zooplankton are highly vulnerable to ambient solar radiation, as a consequence of the combination of high incident radiation and high water transparency allowing deep penetration of damaging UV-B radiation. These results provide evidence of the significance of ambient solar radiation levels as a stressor of marine zooplankton communities in tropical, oligotrophic waters. Because the oligotrophic ocean extends across 70% of the ocean surface, solar radiation can be a globally-significant stressor for the ocean ecosystem, by constraining zooplankton use of the upper levels of the water column and, therefore, the efficiency of food transfer up the food web in the oligotrophic ocean.     

Response of antioxidant defense system to laser radiation apical meristem of Isatis indigotica seedlings exposed to UV-B

To determine the response of antioxidant defense system to laser radiation apical meristem of Isatis indigotica seedlings, Isatis indigotica seedlings were subjected to UV-B radiation (10.08 kJ m⁻²) for 8 h day⁻¹ for 8 days (PAR, 220 µmol m⁻² s⁻¹) and then exposed to He-Ne laser radiation (633 nm; 5.23 mW mm⁻²; beam diameter: 1.5 mm) for 5 min each day without ambient light radiation. Changes in free radical elimination systems were measured, the results indicate that: (1) UV-B radiation enhanced the concentration of Malondialdahyde (MDA) and decreased the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in seedlings compared with the control. The concentration of MDA was decreased and the activities of SOD, CAT and POD were increased when seedlings were subjected to elevated UV-B damage followed by laser; (2) the concentration of UV absorbing compounds and proline were increased progressively with UV-B irradiation, laser irradiation and He-Ne laser irradiation plus UV-B irradiation compared with the control. These results suggest that laser radiation has an active function in repairing UV-B-induced lesions in seedlings.Key words: Isatis indigotica, laser, UV-B lesion     

Responses of aquatic algae and cyanobacteria to solar UV-B

Continuous depletion of the stratospheric ozone layer has resulted in an increase in solar ultraviolet-B (UV-B; 280–315 nm) radiation reaching the Earth's surface. The consequences for aquatic phototrophic organisms of this small change in the solar spectrum are currently uncertain. UV radiation has been shown to adversely affect a number of photochemical and photobiological processes in a wide variety of aquatic organisms, such as cyanobacteria, phytoplankton and macroalgae. However, a number of photosynthetic organisms counteract the damaging effects of UV-B by synthesizing UV protective compounds such as mycosporine-like amino acids (MAAs) and the cyanobacterial sheath pigment, scytonemin. The aim of this contribution is to discuss the responses of algae and cyanobacteria to solar UV-B radiation and the role of photoprotective compounds in mitigating UV-B damage.     

The effects of ultraviolet-B radiation on loblolly pine

Summary Depletion of stratospheric ozone and the resulting increase in ultraviolet-B (UV-B) radiation may negatively impact the productivity of terrestrial ecosystems. This concern has led to a number of studies that report the influence of supplementing UV-B radiation on plant growth and development. However, only two of these field studies have included tree species and both were singleseason experiments. In this study, loblolly pine (Pinus taeda L.) from seven seed sources was grown under natural and supplemental levels of UV-B radiation. Irradiation treatments were continued for three seasons on plants from four of the seven groups and for 1 year only for three groups. The supplemental irradiances simulated those that would be anticipated with stratospheric ozone reductions of 16% and 25% over Beltsville, Md. The effects of UV-B radiation during the 1st year on plant growth varied among the seed sources. The growth of plants from two of the seven seed sources tested showed significant reductions following a single irradiation season and plants from one group tended to be larger under increased UV-B radiation. However, after 3 years of supplemental irradiation, plant biomass was reduced in all four groups by 12–20% at the highest simulated ozone depletion. These results suggest that the effects of UV-B radiation may accumulate in trees and that increased UV-B radiation could significantly reduce the growth of loblolly pine over its lifetime. However, they also point to a need for multiple season research in any analysis of potential consequences of global change on the long-term growth of trees.     

UV damage to plant life in a photobiologically dynamic environment: the case of marine phytoplankton

The effect of UV-B radiation on growth of marine phytoplankton was investigated in relation to DNA damage induced by a range of biologically effective doses (BEDs). Emiliania huxleyi (Prymnesiophyceae) was chosen as a model organism of the ocean's phytoplankton because of its importance in global biogeochemical cycling of carbon and sulphur, elements that influence the world's climate as components of the trace gases carbon dioxide (CO₂) and dimethylsulfide (DMS). A marine diatom, Cyclotella, was studied for its capacity to repair the DNA damage, quantified as thymine dimers by the application of a monoclonal antibody against these photoproducts. DNA repair was shown to be complete after just a few hours of exposure to visible light; the repair rate increased with PAR intensity. E. huxleyi appeared to be most sensitive to UV-B radiation: growth was already affected above a dose of 100 J m^-2 d^-1 (biologically effective radiation, weighted with Setlow's DNA action spectrum), probably through effects on the cell cycle related to damage to nuclear DNA: mean specific growth rates were inversely correlated with thymine dimer contents in cells. Near the ocean's surface UV-B radiation conditions that induce the changes observed by us in cultures can be expected during the growing season of phytoplankton, not only in the tropics but also at higher latitudes. Nevertheles, blooms of species such as E. huxleyi are often excessive in the field. It is suggested that exposure duration of cells near the surface of the ocean can be shorter than our artificial 3 h in the laboratory due to vertical mixing, a phenomenon that is typical for the ocean's upper 50–100 m. When mixing reaches depths greater than the layer where most UV-B is attenuated, negative effects on cells through UV-A-induced inhibition of photosynthesis may prevail over DNA damage, the action spectrum of which has been shown to be limited to the UV-B part of the spectrum. Moreover, the radiation wavelengths that induce DNA damage repair (UV-A and visible) are attenuated vertically much less than UV-B. The photobiological situation in the upper ocean is much more complicated than on land, and effects of UV radiation on plankton biota can only be modelled realistically here when both the spectrally differential attenuation in the UV and visual part of the spectrum and the rate of vertical mixing are taken into account. Action spectra of both damage and repair of DNA and of photosynthesis inhibition of representative microalgal species are the second conditio sine qua non if we want to predict the effect of stratospheric ozone depletion on marine phytoplankton performance.     

Risk of Eye Damage from the Wavelength-Dependent Biologically Effective UVB Spectrum Irradiances

A number of previous studies have discussed the risk of eye damage from broadband ultraviolet (UV) radiation. As the biologically damaging effectiveness of UV irradiation on the human body is known to be wavelength-dependent, it is necessary to study the distribution of the UV spectral irradiance. In order to quantify the ocular biologically effective UV (UVBE) irradiance exposure of different wavelengths and assess the risk of eye damage, UV exposure values were measured at Sanya, China (18.4° N, 109.7°E, altitude 18 m), using a manikin and a dual-detector spectrometer to measure simultaneously the ocular exposure and ambient UV spectral irradiance data and solar elevation angle (SEA) range (approximately 7°–85°). The present study uses the ocular UV spectral irradiance exposure weighted with the action spectra for photokeratitis, photoconjunctivitis and cataracts to calculate the ocular UVBE irradiance exposure for photokeratitis (UVBE_pker), photoconjunctivitis (UVBE_pcon) and cataracts (UVBE_cat). We found that the ocular exposure to UV irradiance is strongest in the 30°–60° SEA range when ∼50% of ocular exposure to UV irradiance on a summer’s day is received. In the 7°–30° SEA range, all the biologically highly effective wavelengths of UVBE_pker, UVBE_pcon and UVBE_cat irradiances are at 300 nm. However, in other SEA ranges the biologically highly effective wavelengths of UVBE_pker, UVBE_pcon and UVBE_cat irradiances are different, corresponding to 311 nm, 300 nm and 307 nm, respectively.     

Effects of UV-B radiation on a charophycean alga,Chara aspera

The charophycean algal species Chara aspera was exposed for 73 days to three levels of UV-B radiation (weighted according to Caldwell's generalized plant action spectrum): 1.9 kJ m^–2 day^–1 (`no UV-B'), 6.4 KJ m<sup>–2</sup> day<sup>–1</sup> (ambient) and 10.5 kJ m<sup>–2</sup> day<sup>–1</sup> (enhanced UV-B), the latter level simulating 30% ozone reduction in The Netherlands.Charophycean algae are mainly freshwater organisms and are thought to be the algae most closely related to higher land plants. Therefore we expected that responses of charophycean algae to UV-B radiation might be more related to those observed in the higher land plants than those of other `lower' algal groups.Under elevated UV-B radiation algal length was reduced. There was no induction of UV absorbing compounds under enhanced UV-B. This might relate to a sensitive response to UV-B radiation. The charophycean algae show similar adaptations to UV-B radiation as terrestrial plants, while not having UV-screens as occur in many angiosperms. Vegetative reproduction (bulbils) increased in the presence of UV-B radiation, while generative reproduction (antheridia and oogonia) decreased.