Use of Radiolabelled Thymidine and Leucine To Estimate Bacterial Production in Soils from Continental Antarctica

Tritiated thymidine incorporation (TTI) into DNA was used to examine bacterial production in two soil types from the Robertskollen group of nunataks in northwestern Dronning Maud Land, providing the first estimates of bacterial production in soil habitats on the Antarctic continent. Although estimates of bacterial productivity in soils near to bird nests (344 (plusmn) 422 ng of C g [dry weight](sup-1) h(sup-1)) were higher than those for soils from beneath mosses (175 (plusmn) 90 ng of C g [dry weight](sup-1) h(sup-1); measured by TTI at 10(deg)C), these differences were not significant because of patchiness of bacterial activity (P > 0.05). TTI- and [(sup14)C]leucine ([(sup14)C]Leu)-derived estimates of bacterial production were similar when incubations of 3 h were used, although incubations as short as 1 h were sufficient for measurable uptake of radiolabel. Dual-label incorporation of [(sup3)H]thymidine ([(sup3)H]TdR) into DNA and [(sup14)C]Leu into protein indicated that TTI did not reflect bacterial production of in situ assemblages when incubations were longer than 3 h. Isotope dilution analysis indicated that dilution of the specific activity of exogenously supplied [(sup3)H]TdR by de novo synthesis of TdR precursor could be limited by additions of [(sup3)H]TdR at a concentration of 1 nmol per ca. 115 mg of soil. TTI exhibited a psychrotrophic response to variation in temperature, with a temperature optimum of ca. 15(deg)C and a Q(inf10) value for 0 to 10(deg)C of 2.41.     

Inorganic Phosphorus Stimulation of Bacterioplankton Production in a Meso-Eutrophic Lake

Experiments were conducted to determine whether production of heterotrophic bacterioplankton in a small meso-eutrophic lake was influenced by the dissolved inorganic phosphorus (DIP) supply. DIP may indirectly limit bacterial production by limiting phytoplankton, which in turn may limit the carbon available to bacteria. Direct DIP limitation of bacteria occurs where the availability of DIP for bacteria is insufficient to maintain growth. This work examined direct DIP limitation of bacteria by removing phytoplankton and incubating flasks with or without added P in the dark. Bacterial production was measured via the rate of incorporation of [³H]thymidine ([³H]TdR) into DNA. Bacterial abundance was followed with epifluorescent direct counts. Rates of [³H]TdR incorporation were significantly greater in flasks with added DIP, and changes in cell abundances generally paralleled increases in [³H]TdR incorporation. Even very small additions of P (0.05 μM) were sufficient to stimulate production. DIP addition to whole lakewater also stimulated [³H]TdR incorporation relative to that in zero-addition controls, but there was not a concurrent increase in bacterial cell numbers. The stimulation of [³H]TdR incorporation after DIP addition to whole lakewater was significantly less than the stimulation due to DIP addition to 1-μm-pore-size-filtered lakewater. In this study, addition of DIP caused as much as an eightfold stimulation of [³H]TdR incorporation.     

Role of ultraviolet-B radiation on bacterioplankton and the availability of dissolved organic matter

Attenuation of ultraviolet (UV)-radiation into the water column is highly correlated with the concentration of the dissolved organic matter (DOM). Thus UV penetrates deeper into marine waters than into freshwater systems. DOM is efficiently cleaved by solar surface radiation levels consuming more oxygen than bacterial metabolism. This photolytically cleaved DOM exhibits higher absorbance ratios (250/365 nm) than untreated DOM. Natural bacterioplankton reach higher abundance if inoculated in previously solar-exposed DOM than in untreated DOM; during bacterial growth the absorbance ratio declines steadily indicating the utilization of the photolytically cleaved DOM. On the other hand, bacterioplankton are greatly reduced in their activity if exposed to surface solar radiation levels. Photoenzymatic repair of DNA induced by UV-A radiation, however, leads to an efficient recovery of bacterial activity once the UV-B stress is released. Turbulent mixing of the upper layers of the water column leads to a continuous alteration of the UV exposure regime. Close to the surface, bacteria and DOM are exposed to high levels of UV-B leading to a reduction in bacterial activity and to photolysis of DOM. Once mixed into deeper layers where UV-B is attenuated, but sufficient UV-A is remaining to allow photoenzymatic repair, the photolytically cleaved DOM is efficiently taken up by bacterioplankton leading to even higher bacterial activity than prior to the exposure. Thus, the overall effect of UV on bacterioplankton is actually an enhancement of bacterial activity despite their lack of protective pigments.     

Endogenous regulation of endothelial cell proliferation

Bovine aortic endothelial cells (BAEC) in culture have the ability to regulate their own proliferation. We have found that a fraction below 100,000 daltons obtained from the media of confluent cultures of BAEC inhibits tritiated thymidine [3H]TdR incorporation as well as their proliferation. The inhibition is dose- and time-dependent; maximum inhibition of [3H]TdR incorporation occurs 8 hr after cells are released from synchronization and the inhibitory fraction is added. Inhibition is evident at concentrations as low as 50 micrograms/ml and reaches a maximum at 600 micrograms/ml. The blockage of [3H]TdR incorporation is reflected in the inhibition of cell proliferation. In the presence of 400 micrograms of endogenous inhibitor per ml of media, added at the time of plating, the average population doubling time increases from 19 to 41 hr. These findings indicate that, in culture, BAEC can regulate their own proliferation by synthesizing an endogenous inhibitor(s) of proliferation.     

Solar UV radiation modulates daily production and DNA damage of marine bacterioplankton from a productive upwelling zone (36°S), Chile

In upwelling ecosystems, such as the Humboldt Current system (HCS) off Concepción, the effects of solar radiation on bacterioplankton incorporation rates have been related to previous light acclimation and responses to irradiance. In this paper, we study the daily effect of Photosynthetic Active Radiation (PAR, 400-700 nm) and ultraviolet radiation UVR (280-400 nm) on bacterial secondary production (BSP). We also considered the DNA damage-repair response to solar radiation stress by the induction of cyclobutane pyrimidine dimers (CPDs). Experiments were conducted with natural bacterioplankton assemblages (0.2-0.7 μm) collected off Concepción (36°S), during the austral Spring, October-November, 2004. Surface (0.5 m) and subsurface (80 m) bacterioplankton samples were exposed to different solar radiation treatments for 5-20 h. BSP was estimated by ¹⁴C-leucine and ³H-thymidine incorporation at several time intervals, whereas CPDs accumulation was assessed using immunoassay techniques. During high irradiance periods, BSP was mainly affected by PAR in both surface and subsurface assemblages and, to a lesser, but significant (Tukey < 0.05) extent, by UV-A (320-400 nm) and UV-B (280-320 nm) radiation. Maximum inhibition of BSP in surface waters was 78%; growth rates (μ) and bacterial growth efficiency (BGE) were also low (78% and 66% respectively). Subsurface water assemblages, on the contrary, showed a ∼ 25 fold enhancement of BSP, μ, and BGE. Both types of assemblages had a rapid CPDs accumulation (maximum 60 CPDs Mb^− 1) during high irradiance periods. Recovery of BSP inhibition and DNA damage in surface bacteria was total after sunset and after the night incubation period, resembling pre-exposure levels. Despite subsurface BSP enhancement during day-night exposure, residual DNA damage was detected at the end of the experiment (20 CPDs Mb^− 1) suggesting a chronic DNA damage. Our results represent the worst case scenario (i.e., assemblages receiving surface irradiances as may occur in this upwelling zone) and indicate that surface and subsurface bacterial assemblages in the HCS are both highly sensitive to solar irradiance. However, they showed different responses, with surface bacteria having more effective photorepair mechanisms, and sustaining higher BSP than subsurface assemblages.     

Arginine deprivation in KB cells: I. Effect on cell cycle progress

When exponentially growing KB cells were deprived of arginine, cell multiplication ceased after 12 h but viability was maintained throughout the experimental period (42-48 h). Although tritiated thymidine ([(3)H]TdR) incorporation into acid-insoluble material declined to 5 percent of the initial rate, the fraction of cells engaged in DNA synthesis, determined by autoradiography, remained constant throughout the starvation period and approximately equal to the synthesizing fraction in exponentially growing controls (40 percent). Continous [(3)H]TdR-labeling indicated that 80 percent of the arginine-starved cells incorporated (3)H at some time during a 48-h deprivation period. Thus, some cells ceased DNA synthesis, whereas some initially nonsynthesizing cells initiated DNA synthesis during starvation. Flow microfluorometric profiles of distribution of cellular DNA contents at the end of the starvation period indicated that essentially no cells had a 4c or G2 complement. If arginine was restored after 30 h of starvation, cultures resumed active, largely asynchronous division after a 16-h lag. Autoradiographs of metaphase figures from cultures continuously labeled with [(3)H]TdR after restoration indicated that all cells in the culture underwent DNA synthesis before dividing. It was concluded that the majority of cells in arginine-starved cultures are arrested in neither a normal G1 nor G2. It is proposed that for an exponential culture, i.e. from most positions in the cell cycle, inhibition of cell growth after arginine with withdrawal centers on the ability of cells to complete replication of their DNA.     

A correction: inhibitory activity in the conditioned medium of embryonic chick bones is due to thymidine

Earlier studies from this laboratory suggested that embryonic chick bones in organ culture released into the culture medium a specific inhibitor of bone cell proliferation as defined by inhibition of [3H]TdR incorporation into DNA. Dialysis and membrane ultrafiltration experiments suggested that the inhibitory substance (IS) had a molecular weight between 6000 and 14,000. However, subsequent studies on the purification of IS have revealed that the inhibitory activity in bone-conditioned medium is of lower molecular weight and has several properties in common with thymidine (TdR): (1) IS coeluted with [3H]TdR upon gel filtration chromatography on Sephadex G-10. (2) IS bound to charcoal but not to cation or anion exchange resins. (3) Bone-conditioned medium decreased incorporation of [3H]TdR into the free [3H]TdR pool of cells in monolayer culture. (4) Conditioned medium inhibited [3H]TdR incorporation into [3H]thymidine monophosphate in a reaction catalyzed by thymidine kinase. The equivalent concentration of TdR in conditioned medium as estimated by thymidine kinase assay was sufficient to account for the reduction in [3H]TdR incorporation into bone cell DNA. No evidence was found for a specific inhibitor of bone cell proliferation other than TdR. Hence we conclude that the inhibitory effect of IS is due to dilution of [3H]TdR by nonradioactive TdR. Furthermore, media conditioned by several tumor cell lines also contained a low-molecular-weight component which inhibited [3H]TdR incorporation. The results suggest that organ- and cell-conditioned media can contain significant concentrations of TdR which can artifactually inhibit [3H]TdR incorporation in cell proliferation assays.     

Photosynthesis and growth of Arthrospira (Spirulina) platensis (Cyanophyta) in response to solar UV radiation, with special reference to its minor variant

The minor variant of the economically important cyanobacterium, Arthrospira platensis, usually appears in commercial production ponds under solar radiation. However, how sensitive the minor variant to solar UVR and whether its occurrence relates to the solar exposures are not known. We investigated the photochemical efficiency of PSII and growth rate of D-0083 strain and its minor variant in semi-continuous cultures under PAR (400–700 nm) alone, PAR + UV-A (320–400 nm) and PAR + UV-A + UV-B (280–700 nm) of solar radiation. The effective quantum yield of D-0083 at 14:00 p.m. decreased by about 86% under PAR, 87% under PAR + UV-A and 92% under PAR + UV-A + UV-B (280–315 nm), respectively. That of the minor variant was reduced by 93% under PAR and to undetectable values in the presence of UV-A or UV-A + UV-B. Diurnal change of the yield showed constant pattern during long-term (10 days) exposures, high in the early morning and late afternoon but the lowest at noontime in both strains, with the UVR-related inhibition being always higher in the variant than D-0083. During the long-term exposures, cells of D-0083 acclimated faster to solar UV radiation and showed paralleled growth rates among the treatments with or without UVR at the end of the experiment; however, growth of the minor variant was significantly reduced by UV-A and UV-B throughout the period. Comparing to the major strain D-0083, the minor variant was more sensitive to UVR in terms of its growth, quantum yield and acclimation to solar radiation.     

Endogenous Regulation of Endothelial Cell Proliferation

Bovine aortic endothelial cells (BAEC) in culture have the ability to regulate their own proliferation. We have found that a fraction below 100,000 daltons obtained from the media of confluent cultures of BAEC inhibits tritiated thymidine [³H]TdR incorporation as well as their proliferation. the inhibition is dose- and time-dependent; maximum inhibition of [³H]TdR incorporation occurs 8 hr after cells are released from synchronization and the inhibitory fraction is added. Inhibition is evident at concentrations as low as 50 μg/ml and reaches a maximum at 600 μg/ml. the blockage of [³H]TdR incorporation is reflected in the inhibition of cell proliferation. In the presence of 400 μg of endogenous inhibitor per ml of media, added at the time of plating, the average population doubling time increases from 19 to 41 hr. These findings indicate that, in culture, BAEC can regulate their own proliferation by synthesizing an endogenous inhibitor(s) of proliferation.     

Effects of temperature, pH, and UV radiation on alkaline phosphatase activity in the terrestrial cyanobacterium Nostoc flagelliforme

Cyanobacteria produce phosphatases in response to phosphorus deficiency as some other autotrophs. However, little has been documented on the effects of key climate change factors, such as temperature rise and solar UV radiation (280–400 nm), on cyanobacterial alkaline phosphatase activity. Here, we found that the terrestrial cyanobacterium Nostoc flagelliforme showed higher activity of the enzyme with increasing temperature and pH levels, exhibiting maximal values at 45 °C and pH?11, respectively. However, when exposed to solar radiation in the presence of UV-A (320–400 nm) and UV-B (280–320 nm), significant reduction of the enzyme activity was observed at a photosynthetically active radiation (PAR) level of 300 W?m^?2 (1,450 μmol photons m^?2 s^?1), which is equivalent or lower than the noontime level of solar PAR at the organism's habitats. UV-A and UV-A + UV-B induced about 21 and 39 % inhibition of the enzyme activity in the 3-h exposures. The decrease in the activity of phosphatase can be attributed to the UV radiation-induced inactivation of the enzyme and indirectly to the UV radiation-induced production of reactive oxygen species.     

Modulation of the bacterial response to spectral solar radiation by algae and limiting nutrients

SUMMARY 1. The response of bacterial production (measured as [³H]TdR incorporation rate) to spectral solar radiation was quantified experimentally in an oligotrophic high-mountain lake over 2 years. Bacterial responses were consistent: ultraviolet-B (UVB) was harmful, whereas ultraviolet-A (UVA) + photosynthetically active radiation (PAR) and PAR enhanced bacterial activity. Full sunlight exerted a net stimulatory effect on bacterial activity in mid-summer but a net inhibitory effect towards the end of the ice-free period.
2. Experiments were undertaken to examine whether the bacterial response pattern depended on the presence of algae and/or was modulated by the availability of a limiting inorganic nutrient (phosphorus, P). In the absence of algae, [³H]TdR incorporation rates were significantly lower than when algae were present under all light treatments, and the consistent bacterial response was lost. This suggests that the bacterial response to spectral solar radiation depends on fresh-C released from algae, which determines the net stimulatory outcome of damage and repair in mid-summer.
3. In the absence of algae, UVB radiation inhibited bacteria when they were strongly P-deficient (mean values of N : P ratio: 46.1), whereas it exerted no direct effect on bacterial activity when they were not P-limited.
4. P-enrichment of lake water markedly altered the response of bacteria to spectral solar radiation at the end of ice-free period, when bacteria were strongly P-deficient. Phosphorus enrichment suppressed the inhibitory effect of full sunlight that was observed in October, both in whole lake water (i.e. including algae) and in the absence of algae. This indicates that the bacterial P-deficiency, measured as the cellular N : P ratio, was partly responsible for the net inhibitory effect of full sunlight, implying a high bacterial vulnerability to UVB.     

Effect of cycloheximide on protein and ribonucleic acid synthesis in cultured human lymphocytes

1. Phytohaemagglutinin stimulates the transformation into blast cells of human lymphocytes incubated in vitro. This transformation is accompanied by an increase in the incorporation of [(14)C]leucine into protein and [(3)H]uridine into RNA. 2. The incorporation of [(14)C]leucine by cultures grown in the presence or absence of phytohaemagglutinin is inhibited to the same extent by cycloheximide, a known inhibitor of protein synthesis. 3. Lymphocytes grown without phytohaemagglutin synthesize mainly non-ribosomal RNA. [(3)H]Uridine incorporation by these cells was increased by cycloheximide. 4. Lymphocytes incubated with phytohaemagglutinin begin to synthesize substantial quantities of ribosomal RNA. Under these conditions [(3)H]uridine incorporation was partially inhibited by cycloheximide. This inhibition is shown to be largely a result of inhibition of the synthesis of ribosomal RNA.     

Application of Microautoradiography to the Study of Substrate Uptake by Filamentous Microorganisms in Activated Sludge

Excessive growth of filamentous microorganisms in activated-sludge treatment plants is a major operational problem which causes poor settlement of activated sludge. An enhanced understanding of the factors controlling growth of different filamentous microorganisms is necessary in order to establish more successful control strategies. In the present study, the in situ substrate uptake was investigated by means of microautoradiography. It was demonstrated that the uptake of labeled organic substrates by the filamentous microorganisms, during short-term incubation, could be detected by microautoradiography. Viability and respiratory activity of the filaments were also detected by reduction of CTC (5-cyano-2,3-ditolyl tetrazolium chloride) and by incorporation of [(sup3)H]thymidine. Gram, Neisser, and fluorescence staining techniques were used for the localization and identification of the filaments. Activated-sludge samples from five wastewater treatment plants with bulking problems due to filamentous microorganisms were investigated. Microthrix parvicella, Nostocoida limicola, and Eikelboom's type 0041 and type 021N were investigated for their ability to take up organic substrates. A panel of six substrates, i.e., [(sup14)C]acetate, [(sup3)H]glucose, [(sup14)C]ethanol, [(sup3)H]glycine, [(sup3)H]leucine, and [(sup3)H]oleic acid, was tested. The uptake response was found to be very specific not only between the different filamentous types but also among filaments of the same type from different treatment plants. Interestingly, M. parvicella consistently took up only oleic acid among the tested substrates. It is concluded that microautoradiography is a useful method for investigation of in situ substrate uptake by filamentous microorganisms in activated sludge.     

Double labelling of tissue combining tritiated thymidine autoradiography with immunodetection of bromodeoxyuridine: the autoradiographic significance of inhibition of thymidine incorporation into DNA by bromodeoxyuridine given simultaneously

We describe a reproducible method for combining tritiated thymidine ([H]TdR) autoradiography with immunoperoxidase detection of bromodeoxyuridine (BrdU) in paraffin-embedded tissues. The technique has been used to examine, in mouse tongue epithelium, the inhibition of incorporation into DNA of [3H]TdR by a simultaneous injection of BrdU in the doses that both compounds are likely to be used in cell proliferation studies. The significance that this inhibition has on prolongation of autoradiograph exposure times, to ensure that all cells that incorporate [3H]TdR are scored as positive, in particular the most lightly labelled cells, has been quantified. The inhibition of uptake into DNA of [3H]TdR from 0.23 to 1.85 MBq (6.25 to 50 mu Ci) per animal, produced by a simultaneous injection of 2.5 mg BrdU shows a linear, dose-dependent relationship. Provided the injected dose (in mu Ci per animal) multiplied by the autoradiographic exposure time (in days) is greater than a value of 700, then all cells that are labelled after incorporation of [3H]TdR alone are also labelled after simultaneous double labelling, despite the latter producing a lower average grain count.     

Row orientation effect on UV-B,UV-A and PAR solar irradiation components in vineyards at Tuscany,Italy

Besides playing an essential role in plant photosynthesis, solar radiation is also involved in many other important biological processes. In particular, it has been demonstrated that ultraviolet (UV) solar radiation plays a relevant role in grapevines (Vitis vinifera) in the production of certain important chemical compounds directly responsible for yield and wine quality. Moreover, the exposure to UV-B radiation (280–320 nm) can affect plant–disease interaction by influencing the behaviour of both pathogen and host. The main objective of this research was to characterise the solar radiative regime of a vineyard, in terms of photosynthetically active radiation (PAR) and UV components. In this analysis, solar spectral UV irradiance components, broadband UV (280–400 nm), spectral UV-B and UV-A (320–400 nm), the biological effective UVBE, as well as the PAR (400–700 nm) component, were all considered. The diurnal patterns of these quantities and the UV-B/PAR and UV-B/UV-A ratios were analysed to investigate the effect of row orientation of the vineyard in combination with solar azimuth and elevation angles. The distribution of PAR and UV irradiance at various heights of the vertical sides of the rows was also studied. The results showed that the highest portion of plants received higher levels of daily radiation, especially the UV-B component. Row orientation of the vines had a pronounced effect on the global PAR received by the two sides of the rows and, to a lesser extent, UV-A and UV-B. When only the diffused component was considered, this geometrical effect was greatly attenuated. UV-B/PAR and UV-A/PAR ratios were also affected, with potential consequences on physiological processes. Because of the high diffusive capacity of the UV-B radiation, the UV-B/PAR ratio was significantly lower on the plant portions exposed to full sunlight than on those in the shade.     

Inhibition of phytoplankton photosynthesis by solar ultraviolet radiation: studies in Lake Titicaca, Bolivia

1. Lake Titicaca is a large, high altitude (3810 m a.s.l.) tropical lake (16°S, 68°W) that lies on the border of Bolivia and Perú, receiving high fluxes of ultraviolet radiation (UVR) throughout the year. Our studies were conducted during September of 1997 with the main objective of studying the impact of solar UVR upon phytoplankton photosynthesis.
2. Water samples were taken daily and incubated in situ (down to 14 m depth) under three radiation treatments to study the relative responses to PAR (Photosynthetic Available Radiation, 400–700 nm), UV-A (320–400 nm), and UV-B (280–320 nm) radiation.
3. Photosynthetic inhibition by UVR in surface waters was about 80%, with UV-A accounting for 60% and UV-B for 20%; the inhibition by high levels of PAR was less than 20%. The inhibition due to UVR decreased with depth so that there were no significant differences between treatments at 8.5 m depth.
4. The amount of inhibition per unit energy received by phytoplankton indicates that even though there was a significant inhibition of photosynthesis due to UVR, species in Lake Titicaca seem to be better adapted than species in high latitude environments.
5. The cellular concentration of UV-absorbing compounds, a possible mechanism of photoadaptation, was low in phytoplanktonic species. However, they were abundant in zooplankton, suggesting a high rate of bioaccumulation through the diet.     

Enhancement in leghemoglobin content of root nodules by exclusion of solar UV-A and UV-B radiation in soybean

The impact of exclusion of solar UV-B (280–320 nm) and UV-A+B (280–400 nm) radiation on the root nodules was studied in soybean(Glycine max var. MACS 330). Soybean plants were grown in the tropical region of Indore (Latitude-22.4°N), India under field conditions in metal cages covered with polyester exclusion filters that specifically cut off UV-B (<320 nm) and UV-A+B (<400 nm) radiation; control plants were grown under ambient solar radiation. Leghemoglobin content was analyzed in the root nodules on the 50^th day after emergence of seedlings. Exclusion of UV radiations significantly enhanced the leghemoglobin content in the nodules on fresh weight basis; 25% and 45% higher amount of leghemoglobin were present in the nodules after the exclusion of UV-B and UV-A+B radiation respectively. Analysis by native and SDS-PAGE showed high intense bands of leghemoglobin after the exclusion of UV-A+B as compared to control. Exclusion of UV radiation also enhanced the growth of roots as well as aerial parts of the plants. UV Exclusion increased nodulation by increase in the number and size of nodules. The results are discussed in the light of advantage of exclusion for enhancing protein/nitrogen content in the plants.     

Spectral balance and UV-B sensitivity of soybean: a field experiment

Soybean [Glycine max (L.) Merr.] cultivar Essex was grown and tested for sensitivity to UV-B radiation (280–320 nm) under different combinations of UV-A (320–400 nm) and PFD (400–700 nm) radiation in four simultaneous field experiments. The radiation conditions were effected with combinations of filtered solar radiation and UV-B and UV-A lamps electronically modulated to track ambient radiation. Significant UV-B-caused decreases in total aboveground production and growth were seen only when PFD and UV-A were reduced to less than half their flux in sunlight. When PFD was low, UV-A appeared to be particularly effective in mitigating UV-B damage. However, when PFD was high, substantial UV-A did not appear to be required for UV-B damage mitigation. Leaf chlorophyll fluorescence did not indicate photosynthetic damage under any radiation combination. With UV-B, leaves in all experiments exhibited increased UV-absorbing pigments and decreased whole-leaf UV transmittance. Results of these field experiments indicate difficulties in extrapolating from UV-B experiments conducted in glasshouse or growth cabinet conditions to plant UV-B sensitivity in the field. Implications for UV radiation weighting functions in evaluating atmospheric ozone reduction are also raised.     

Influence of solar ultraviolet radiation on photosynthesis and motility of marine phytoplankton

Abstract: The effects of solar ultraviolet radiation (UV) on carbon uptake, oxygen evolution and motility of marine phytoplankton were investigated in coastal waters at Kristineberg Marine Research Station on the west coast of Sweden (58° 30'N, 11° 30'E). The mean irradiances at noon above the water surface during the investigation period were: photosynthetic active radiation (PAR, 400–700 nm) 1670 μmol m⁻² s⁻¹; ultraviolet-A radiation (UV-A, 320–400 nm) 35.9 W m⁻² and ultraviolet-B radiation (UV-B, 280–320 nm) 1.7 W m⁻². UV-B radiation was much more attenuated with depth in the water column than were PAR and UV-A radiation. UV-B radiation could not be detected at depths greater than 100–150 cm. Inhibition of carbon uptake by UV-A and UV-B in natural phytoplankton populations was greatest at 50 cm depth and the effects of UV-B were greater than those of UV-A. At depths greater than 50 cm there was almost no effect of ultraviolet radiation on carbon uptake. PAR, UV-A and UV-B decreased oxygen evolution by the dinoflagellate Prorocentrum minimum . Inhibition of oxygen evolution was greater after 4 h than 2 h but it was not possible to distinguish the negative effects of the different light regimes. The motility of P. minimum was not affected by PAR, UV-A and UV-B. The importance of exposure of phytoplankton to different light regimes before being exposed to natural solar radiation is discussed.