DIFFERENTIAL RESPONSES OF ANABAENA SP. PCC 7120 (CYANOPHYCEAE) CULTURED IN NITROGEN‐DEFICIENT AND NITROGEN‐ENRICHED MEDIA TO ULTRAVIOLET‐B RADIATION1

Stratospheric ozone depletion increases the amount of ultraviolet‐B radiation (UVBR) (280–320 nm) reaching the surface of the earth, potentially affecting phytoplankton. In this work, Anabaena sp. PCC 7120, a typically nitrogen (N)‐fixing filamentous bloom‐forming cyanobacterium in freshwater, was individually cultured in N‐deficient and N‐enriched media for long‐term acclimation before being subjected to ultraviolet‐B (UVB) exposure experiments. Results suggested that the extent of breakage in the filaments induced by UVBR increases with increasing intensity of UVB stress. In general, except for the 0.1 W · m^?2 treatment, which showed a mild increase, UVB exposure inhibits photosynthesis as evidenced by the decrease in the chl fluorescence parameters maximum photochemical efficiency of PSII (F_v/F_m) and maximum relative electron transport rate. Complementary chromatic acclimation was also observed in Anabaena under different intensities of UVB stress. Increased total carbohydrate and soluble protein may provide some protection for the culture against damaging UVB exposure. In addition, N‐deficient cultures with higher recovery capacity showed overcompensatory growth under low UVB (0.1 W · m^?2) exposure during the recovery period. Significantly increased (～830%) ATPase activity may provide enough energy to repair the damage caused by exposure to UVB.     

DNA damage and photosynthesis in Antarctic and Arctic Sanionia uncinata (Hedw.) Loeske under ambient and enhanced levels of UV-B radiation

The response of the bipolar moss Sanionia uncinata (Hedw.) Loeske to ambient and enhanced UV‐B radiation was investigated at an Antarctic (Léonie Island, 67°35′ S, 68°20′ W) and an Arctic (Ny‐Alesund, 78°55′ N, 11°56′ E) site, which differed in ambient UV‐B radiation (UV‐BR: 280–320 nm) levels. The UV‐BR effects on DNA damage and photosynthesis were investigated in two types of outdoor experiments. First of all, sections of turf of S. uncinata were collected in an Arctic and Antarctic field site and exposed outdoors to ambient and enhanced UV‐BR for 2 d using UV‐B Mini‐lamps. During these experiments, chlorophyll a fluorescence, chlorophyll concentration and cyclobutyl pyrimidine dimer (CPD) formation were measured. Secondly, at the Antarctic site, a long‐term filter experiment was conducted to study the effect of ambient UV‐BR on growth and biomass production. Additionally, sections of moss turf collected at both the Antarctic and the Arctic site were exposed to UV‐BR in a growth chamber to study induction and repair of CPDs under controlled conditions. At the Antarctic site, a summer midday maximum of 2·1 W m^?2 of UV‐BR did not significantly affect effective quantum yield (ΔF/F_m′) and the ratio of variable to maximal fluorescence (F_v/F_m). The same was found for samples of S. uncinata exposed at the Arctic site, where summer midday maxima of UV‐BR were about 50% lower than at the Antarctic site. Exposure to natural UV‐BR in summer did not increase CPD values significantly at both sites. Although the photosynthetic activity remained largely unaffected by UV‐B enhancement, DNA damage clearly increased as a result of UV‐B enhancement at both sites. However, DNA damage induced during the day by UV‐B enhancement was repaired overnight at both sites. Results from the long‐term filter experiment at the Antarctic site indicated that branching of S. uncinata was reduced by reduction of ambient summer levels of UV‐BR, whereas biomass production was not affected. Exposure of specimens collected from both sites to UV‐BR in a growth chamber indicated that Antarctic and Arctic S. uncinata did not differ in UV‐BR‐induced DNA damage. It was concluded that S. uncinata from both the Antarctic and the Arctic site is well adapted to ambient levels of UV‐BR.     

Development of a solar-powered microbial fuel cell

Aims: To understand factors that impact solar‐powered electricity generation by Rhodobacter sphaeroides in a single‐chamber microbial fuel cell (MFC). Methods and Results: The MFC used submerged platinum‐coated carbon paper anodes and cathodes of the same material, in contact with atmospheric oxygen. Power was measured by monitoring voltage drop across an external resistance. Biohydrogen production and in situ hydrogen oxidation were identified as the main mechanisms for electron transfer to the MFC circuit. The nitrogen source affected MFC performance, with glutamate and nitrate‐enhancing power production over ammonium. Conclusions: Power generation depended on the nature of the nitrogen source and on the availability of light. With light, the maximum point power density was 790 mW m^?2 (2·9 W m^?3). In the dark, power output was less than 0·5 mW m^?2 (0·008 W m^?3). Also, sustainable electrochemical activity was possible in cultures that did not receive a nitrogen source. Significance and Impact of the Study: We show conditions at which solar energy can serve as an alternative energy source for MFC operation. Power densities obtained with these one‐chamber solar‐driven MFC were comparable with densities reported in nonphotosynthetic MFC and sustainable for longer times than with previous work on two‐chamber systems using photosynthetic bacteria.     

Discrimination of nitrogen isotopes during absorption of ammonium and nitrate at different nitrogen concentrations by rice (Oryza sativa L.) plants

Studies of uptake of ionic sources of N by two hydroponically grown rice (Oryza sativa L.) cultivars (paddy‐field‐adapted Koshihikari and dryland‐adapted Kanto 168) showed that the magnitude of the nitrogen isotope fractionation (?) for uptake of NH₄⁺ depended on the concentrations of NH₄⁺ and cultivar (averaging –6·1‰ for Koshihikari and –12·0‰ for Kanto 168 at concentrations from 40 to 200 mmol m^?3 and, respectively, –13·4 and –28·9‰ for the two cultivars at concentrations from 0·5 to 4 mol m^?3). In contrast, the ? for uptake of NO₃^? in similar experiments was almost insensitive to the N concentration, falling within a much narrower range (+3·2‰ to –0·9‰ for Koshihikari and –0·9‰ to –5·1‰ for Kanto 168 over NO₃^? concentrations from 0·04 to 2 mol m^?3). From longer term experiments in which Norin 8 and its nitrate‐reductase deficient mutant M819 were grown with 2 or 8 mol m^?3 NO₃^? for 30 d, it was concluded that the small concentration‐independent isotopic fractionation during absorption of this ion was not related to nitrate reductase activity.     

Photosynthates stimulate the UV-B induced fungal anthraquinone synthesis in the foliose lichen Xanthoria parietina

Synthesis of the cortical anthraquinone pigment parietin (= physcion) was studied in acetone‐rinsed, parietin‐free Xanthoria parietina thalli. UV‐B induced the synthesis, which increased linearly with UV‐B (log‐transformed) to the highest applied UV‐B level (1.8 W m^?2). At natural UV‐B levels (0.75 W m^?2), parietin resynthesis occurred at a constant pace (106 mg m^?2 d^?1) during a 14‐d period at 220 µmol m^?2 s^?1 PAR. Under these conditions, 56% of the natural parietin content prior to extraction was resumed, accounting for 10% of total net carbon gain. In the presence of UV‐B, the remaining results were consistent with the hypothesis assuming that photosynthates regulate the pace at which parietin is synthesized by the mycobiont. Resynthesis was rapid when photosynthesis was activated by light, or when certain carbohydrates were added exogenously. Additions of ribitol, the carbohydrate delivered from the photobiont, increased the parietin resynthesis substantially. Mannitol, the main fungal polyol, was significantly less effective. Furthermore, parietin resynthesis in X. parietina was depressed at high and low hydration when net photosynthesis is depressed. Therefore, the photobiont regulates the parietin resynthesis pace in its mycobiont partner by the delivery of photosynthates. In conclusion, both lichen bionts play important roles in the synthesis of parietin, which probably acts as a PAR‐ rather than a UV‐B‐screen.     

INTERACTIVE EFFECTS OF PAR AND UV‐B RADIATION ON PSII ELECTRON TRANSPORT IN THE MARINE ALGA DUNALIELLA TERTIOLECTA (CHLOROPHYCEAE)1

To better understand the interactions between PAR and UV‐B radiation in microalgae, the marine chlorophyte alga Dunaliella tertiolecta was subjected to a UV‐B flux of 4.1 W·m ^{? 2} (unweighted) with varying PAR fluxes. Rate constants for damage and repair processes during UV‐B exposure increased with PAR flux. However, recovery after UV‐B exposure increased with PAR up to 300 μmol quanta·m ^{? 2}·s ^{? 1} 1 Received 17 September 2002. Accepted 19 February 2003. , beyond which photoinhibition of PSII electron transport was found to decrease recovery rates. In the absence of PAR during the post UV‐B exposure period, no recovery was seen, indicating that perhaps the lack of light available for photosynthesis depresses repair either directly or indirectly by affecting ATP synthesis. Possible mechanisms for the observed interactions between PAR and UV‐B exposure are discussed.     

Multivariate analysis of intraspecific responses to UV-B radiation in white clover (Trifolium repens L.)

White clover (Trifolium repens L.) is experiencing increased levels of ultraviolet‐B (UV‐B) radiation in temperate pastures due to the depletion of the stratospheric ozone layer. Based on 17 morphological, morphogenetic and physiological attributes, this study analysed the consequences of enhanced UV‐B on 26 white clover populations using principal components analysis (PCA). After 18 d of exposure to 13·3 kJ m ^{? 2} d ^{? 1} UV‐B in controlled environments, UV‐B significantly decreased above‐ground and below‐ground plant growth attributes, epidermal cell surface area and maximum quantum efficiency of photosystem II photochemistry (F_v/F_m). Aspects of cell division and cell expansion both were negatively affected by UV‐B. Stomatal density, specific leaf mass, root‐to‐shoot ratio and levels of UV‐B‐absorbing compounds increased in response to UV‐B. In the multivariate analysis, the main dimension of UV‐B sensitivity was characterized by changes in plant growth attributes. Alterations in partitioning within and between plant organs constituted a secondary tier of UV‐B responsiveness. Plant characteristics related to UV‐B tolerance included lower growth rate, smaller epidermal cell surface area and higher UV‐B‐induced levels of UV‐B‐absorbing compounds. The results suggest overall UV‐B tolerance for slower‐growing populations from less productive habitats with higher natural UV‐B irradiance.     

Comparison of supplements* to enhance recovery of heat‐injured Salmonella from egg albumen

Aims: The purpose of this study was to determine the proficiency of supplements to enhance the recovery of Salmonella from heat‐treated liquid egg albumen on solid agar media. Methods and Results: Salmonella‐inoculated albumen, heated at 53·3°C for 4 min, was plated on 39 combinations of solid media with or without the addition of 12 supplements. Greater numbers of Salmonella (P < 0·05) recovered with the addition of 1·0 g l^?1 ferrous sulfate (FeSO₄) than with any other supplements, except for 0·5 or 1·0 g l^?1 3′3′‐thiodipropionic acid (TDP), which recovered equivalent populations. Addition of 1·0 g l^?1 sodium pyruvate or 6·0 g l^?1 yeast extract plus 1·0 g l^?1 sodium pyruvate supported greater resuscitation than unsupplemented tryptic soy agar (TSA) or supplementing with 0·01 or 0·1 g l^?1 N‐propyl gallate, 10 g l^?1 activated charcoal, 0·1 g l^?1 KMnO₄ or 50 mg l^?1 ethoxyquin. The remaining supplements supported recovery of equivalent numbers of Salmonella, which were fewer cells than recovered with 1·0 g l^?1 FeSO₄, yet greater populations than recovered with 50 mg l^?1 ethoxyquin. Conclusion: Supplementation of plating media with FeSO₄, TDP or sodium pyruvate enhanced recovery of sublethally injured Salmonella from albumen. Significance and Impact of the Study: Pasteurizing albumen impedes recovery of pathogens. These results suggest that the addition of supplements to plating media may assist resuscitation and colony development of heat‐injured salmonellae.     

MORPHO‐FUNCTIONAL PATTERNS OF PHOTOSYNTHESIS IN THE SOUTH PACIFIC KELP LESSONIA NIGRESCENS: EFFECTS OF UV RADIATION ON 14C FIXATION AND PRIMARY PHOTOCHEMICAL REACTIONS1

The morpho‐functional patterns of photosynthesis, measured as ¹⁴C‐fixation and chl fluorescence of PSII, also as affected by different doses of UV radiation in the laboratory were examined in the South Pacific kelp Lessonia nigrescens Bory of the coast of Valdivia, Chile (40°S). The results indicated the existence of longitudinal thallus profiles in physiological performance. In general, blades exhibited higher rates of carbon fixation and pigmentation as compared with stipes and holdfasts. Light‐independent ¹⁴C fixation (LICF) was high in meristematic zones of the blades (3.5 μmol ¹⁴C·g^?1 fresh weight [FW]·h^?1), representing 2%–16% (percentage ratio) of the photosynthetic ¹⁴C fixation (20 μmol ¹⁴C·g^?1 FW·h^?1). Exposures to UV radiation indicated that biologically effective UV‐B doses (BED_{photoinhibition300}) of 200–400 kJ·m^?2 (corresponding to current daily doses measured in Valdivia on cloudless summer days) inhibit photosynthetic ¹⁴C fixation of blades by 90%, while LICF was reduced by 70%. The percentage ratio of LICF to photosynthetic ¹⁴C fixation increased under UV exposure to 45%. Primary light reactions measured as maximum quantum yield (F_v/F_m) and electron transport rate (ETR) indicated a higher UV susceptibility of blades as compared with stipes and holdfasts: after a 48 h exposure to UV‐B, the decrease in the blades was close to 30%, while in the stipes and holdfasts it was <20%. The existence of translocation of labeled carbon along the blades suggests that growth at the meristem may be powered by nonphotosynthetic processes. A possible functional role of LIFC, such as during reduction of photosynthetic carbon fixation due to enhanced UV radiation, is discussed. These results in general support the idea that the UV‐related responses in Lessonia are integrated in the suite of morpho‐functional adaptations of the alga.     

The onset of photosynthetic acclimation to elevated CO2 partial pressure in field-grown Pinus radiata D. Don. after 4 years

The effects of CO₂ enrichment on photosynthesis and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (rubisco) were studied in current year and 1‐year‐old needles of the same branch of field‐grown Pinus radiata D. Don trees. All measurements were made in the fourth year of growth in large, open‐top chambers continuously maintained at ambient (36 Pa) or elevated (65 Pa) CO₂ partial pressures. Photosynthetic rates of the 1‐year‐old needles made at the growth CO₂ partial pressure averaged 10·5 ± 0·5 μmol m^?2 s^?1 in the 36 Pa grown trees and 11·8 ± 0·4 μmol m^?2 s^?1 in the 65 Pa grown trees, and were not significantly different from each other. The photosynthetic capacity of 1‐year‐old needles was reduced by 25% from 23·0 ± 1·8 μmol m^?2 s^?1 in the 36 Pa CO₂ grown trees to 17·3 ± 0·7 μmol m^?2 s^?1 in the 65 Pa grown trees. Growth in elevated CO₂ also resulted in a 25% reduction in V_cmax (maximum carboxylation rate), a 23% reduction in J_max (RuBP regeneration capacity mediated by maximum electron transport rate) and a 30% reduction in Rubisco activity and content. Total non‐structural carbohydrates (TNC) as a fraction of total dry mass increased from 12·8 ± 0·4% in 1‐year‐old needles from the 36 Pa grown trees to 14·2 ± 0·7% in 1‐year‐old needles from the 65 Pa grown trees and leaf nitrogen content decreased from 1·30 ± 0·02 to 1·09 ± 0·10 g m^?2. The current‐year needles were not of sufficient size for gas exchange measurements, but none of the biochemical parameters measured (Rubisco, leaf chlorophyll, TNC and N), were effected by growth in elevated CO₂. These results demonstrate that photosynthetic acclimation, which was not found in the first 2 years of this experiment, can develop over time in field‐grown trees and may be regulated by source‐sink balance, sugar feedback mechanisms and nitrogen allocation.     

Growth and physiological responses of cotton (Gossypium hirsutum L.) to elevated carbon dioxide and ultraviolet-B radiation under controlled environmental conditions

Better understanding of crop responses to projected changes in climate is an important requirement. An experiment was conducted in sunlit, controlled environment chambers known as soil–plant–atmosphere–research units to determine the interactive effects of atmospheric carbon dioxide concentration [CO₂] and ultraviolet‐B (UV‐B) radiation on cotton (Gossypium hirsutum L.) growth, development and leaf photosynthetic characteristics. Six treatments were used, comprising two levels of [CO₂] (360 and 720 µmol mol^?1) and three levels of 0 (control), 7.7 and 15.1 kJ m^?2 d^?1 biologically effective UV‐B radiations within each CO₂ level. Treatments were imposed for 66 d from emergence until 3 weeks after the first flower stage. Plants grown in elevated [CO₂] had greater leaf area and higher leaf photosynthesis, non‐structural carbohydrates, and total biomass than plants in ambient [CO₂]. Neither dry matter partitioning among plant organs nor pigment concentrations was affected by elevated [CO₂]. On the other hand, high UV‐B (15.1 kJ m^?2 d^?1) radiation treatment altered growth resulting in shorter stem and branch lengths and smaller leaf area. Shorter plants at high UV‐B radiation were related to internode lengths rather than the number of mainstem nodes. Fruit dry matter accumulation was most sensitive to UV‐B radiation due to fruit abscission. Even under 7.7 kJ m^?2 d^?1 of UV‐B radiation, fruit dry weight was significantly lower than the control although total biomass and leaf photosynthesis did not differ from the control. The UV‐B radiation of 15.1 kJ m^?2 d^?1 reduced both total (43%) and fruit (88%) dry weights due to smaller leaf area and lower leaf net photosynthesis. Elevated [CO₂] did not ameliorate the adverse effects of UV‐B radiation on cotton growth and physiology, particularly the boll retention under UV‐B stress.     

Changes in photosynthesis and antioxidant defenses of Picea asperata seedlings to enhanced ultraviolet-B and to nitrogen supply

The paper mainly studied the effects of ultraviolet‐B (UV‐B) radiation, nitrogen, and their combination on photosynthesis and antioxidant defenses of Picea asperata seedlings. The experimental design included two levels of UV‐B treatments (ambient UV‐B, 11.02 KJ m⁻² day⁻¹; enhanced UV‐B, 14.33 KJ m⁻² day⁻¹) and two nitrogen levels (0; 20 g m⁻² a⁻¹ N) – to determine whether the adverse effects of UV‐B are eased by supplemental nitrogen. Enhanced UV‐B significantly inhibited plant growth, net photosynthetic rate (A), stomatal conductance to water vapor (Gs), transpiration rate and photosynthetic pigment, and increased intercellular CO₂ concentration, UV‐B absorbing compounds, proline content, malondialdehyde (MDA) content, and activity of antioxidant enzymes (peroxidase (POD), superoxide dimutase, and glutathione reductase). Enhanced UV‐B also reduced needle DW and increased hydrogen peroxide (H₂O₂) content and the rate of superoxide radical (O₂⁻) production only under supplemental nitrogen. On the other hand, supplemental nitrogen increased plant growth, A, Gs, chlorophyll content and activity of antioxidant enzymes (POD, ascorbate peroxidase, and catalase), and reduced MDA content, H₂O₂ content, and the rate of O₂⁻ production only under ambient UV‐B, whereas supplemental nitrogen reduced activity of antioxidant enzymes under enhanced UV‐B. Carotenoids content, proline content, and UV‐B absorbing compounds increased under supplemental nitrogen. Moreover, significant UV‐B × nitrogen interaction was found on plant height, basal diameter, A, chlorophyll a, activity of antioxidant enzymes, H₂O₂, MDA, and proline content. These results implied that supplemental nitrogen was favorable for photosynthesis and antioxidant defenses of P.asperata seedlings under ambient UV‐B. However, supplemental nitrogen made the plants more sensitive to enhanced UV‐B, although some antioxidant indexes increased.     

Effect of turbulence on feeding intensity and survival of Japanese flounder Paralichthys olivaceus pelagic larvae

Three‐day rearing experiments were conducted to study the effect of turbulence on the feeding intensity and survival of pelagic larvae of Japanese flounder Paralichthys olivaceus. Four levels of turbulence as control (10^?7·2 m² s^?3), low (10^?6·2 m² s^?3), mid (10^?5·6 m² s^?3) and high (10^?5·0 m² s^?3) were set by changing the flow rate of water pumped through pipes set on the bottom of the tanks. In B‐stage larvae, defined as having buds of elongated dorsal fin rays, the feeding intensity and growth were higher in the low and mid turbulence levels, while survival was highest in the control level. Most of the larvae surviving in the control level, however, were judged to be in a seriously starved condition leading to subsequent high mortality. Because the three‐day span of the rearing experiments was thought to be a little shorter than the periods before starvation‐induced, high mortality occurs. In contrast, for D‐stage larvae, their feeding and growth were optimal in the control and low levels. Feeding was more adversely affected in the high level for D‐stage larvae compared with B‐stage larvae. This is probably due to the compressed body shape and elongated dorsal fin rays of D‐stage larvae, which may be more strongly affected by turbulence and, as a consequence, the larval feeding behaviour such as pursuit and capture of prey organisms becomes less efficient than in lower turbulence. Considering the vertical distribution of B and D‐stage larvae in the oceanic water column, the optimum turbulence level range found in the present study corresponded to a wind speed of 7–10 m s^?1. Therefore, moderate weather conditions of this wind speed range are considered to potentially enhance survival of early larval stages of P. olivaceus.     

Sporogenic and vegetative tissues of Saccharina latissima (Laminariales,Phaeophyceae) exhibit distinctive sensitivity to experimentally enhanced ultraviolet radiation : photosynthetically active radiation ratio

Fertile Saccharina latissima sporophytes, collected in the Kongsfjorden, Ny‐Ålesund, Spitsbergen, Norway (78°56.87′ N, 11°51.64′ E) were investigated in relation to its sensitivity to experimentally enhanced ultraviolet radiation : photosynthetically active radiation (UVR : PAR) ratios. Irradiance of UVR were 4.30 W m^?2 of UV‐A (320–400 nm) and 0.40 W m^?2 of UV‐B (280–320 nm), and PAR (400–700 nm) was ～4.30 W m^?2 (=20 µmol photons m^?2 s^?1). Excised soral (sporogenic) and non‐soral (vegetative) tissues were separately irradiated for 16 h at 7°C. Transmission electron microscopy showed abundant occurrence of physodes, electron dense particles (～300–600 nm) in the sorus. Paraphysis cells, with partly crystalline content, large mitochondria and abundant golgi bodies were towering over the sporangia. In soral tissue, cells were not visibly altered by the PAR + UVR irradiation. The chloroplasts, flagella and nucleus of unreleased meiospores inside the sporangial parent cells were visibly intact. Severe changes in the chloroplast structure of vegetative tissue occurred after PAR + UVR irradiation. These changes included wrinkling and dilatation of the thylakoid membranes, and appearance of electron translucent areas inside the chloroplasts. In vegetative cells exposed to PAR + UVR, the total amount of physodes, was slightly higher as in cells exposed to PAR only. Initial values of optimum quantum yield of photosystem II (F_v/F_m) were 0.743 ± 0.04 in non‐soral and 0.633 ± 0.04 in soral tissue. Vegetative tissue was observed to be more sensitive to radiant exposure of PAR and PAR + UVR compared to reproductive tissue. Under PAR, a 20% reduction in Fv/Fm was observed in non‐soral compared to no reduction in soral tissue, whereas under PAR + UVR, 60% and 33% reduction in Fv/Fm was observed in non‐soral and soral tissues, respectively. This can be attributed to the corresponding three times higher antiradical power (ARP) capacity in soral compared to non‐soral tissue.     

A COMPARISON OF PHOTORESPONSE AMONG TEN DIFFERENT KARENIA BREVIS (DINOPHYCEAE) ISOLATES1

Many laboratories have solely used the Wilson isolate to physiologically characterize the harmful algal bloom (HAB) dinoflagellate Karenia brevis (C. C. Davis) G. Hansen et Moestrup. However, analysis of one isolate may lead to misinterpretations when extrapolating measurements to field populations. In this study, pulse‐amplitude‐modulated chlorophyll fluorometer (PAM‐FL) relative electron transport rate (ETR), F_v/F_m, and chl were compared with traditional techniques, such as ¹⁴C photosynthesis versus irradiance (P–E) curves, DCMU [3‐(3′,4′‐dichlorophenyl)‐1,1‐dimethyl urea] F_v/F_m, and extracted chl. The DCMU and PAM‐FL values of F_v/F_m (r² = 0.51) and chl (r² = 0.58) were in good agreement. There was no correlation between ¹⁴C and PAM‐FL α, P_max, and β parameters because PAM‐FL ETR was only a relative measurement. The PAM‐FL techniques were then used to investigate P–E curves, quantum yield of PSII (F_v/F_m), and chl from 10 K. brevis isolates to determine whether one or all isolates would better represent the species. Comparisons were made with a radial photosynthetron, which allowed for controlled conditions of light and temperature. Isolate α, P_max, and β varied between 0.097 and 0.204 μmol e^? · m^?2 · s^?1 · (μmol quanta · m^?2 · s^?1)^?1, 80.41 and 241 μmol e^? · m^?2 · s^?1, and 0.005 and 0.160 μmol e^? · m^?2 · s^?1 · (μmol quanta · m^?2 · s^?1)^?1, respectively. Either carbon limitation and/or bacterial negative feedback were implicated as the cause of the P–E parameter variability. Furthermore, these results directly contradicted some literature suggestions that K. brevis is a low‐light‐adapted dinoflagellate. Results showed that K. brevis was more than capable of utilizing and surviving in light conditions that may be present on cloudless days off Florida.     

Analysis of copper corrosion in compacted bentonite clay as a function of clay density and growth conditions for sulfate‐reducing bacteria

Aims: To investigate the relationships between sulfate‐reducing bacteria (SRB), growth conditions, bentonite densities and copper sulfide generation under circumstances relevant to underground, high‐level radioactive waste repositories. Methods and Results: Experiments took place 450 m underground, connected under in situ pressure to groundwater containing SRB. The microbial reduction of sulfate to sulfide and subsequent corrosion of copper test plates buried in compacted bentonite were analysed using radioactive sulfur (³⁵SO₄^2?) as tracer. Mass distribution of copper sulfide on the plates indicated a diffusive process. The relationship between average diffusion coefficients (D_s) and tested density (ρ) was linear. D_s (m² s^?1) = ?0·004 × ρ (kg m^?3) + 8·2, decreasing by 0·2 D_s units per 50 kg m^?3 increase in density, from 1·2 × 10^?11 m² s^?1 at 1750 kg m^?3 to 0·2 × 10^?11 m² s^?1 at 2000 kg m^?3. Conclusions: It is possible that sulfide corrosion of waste canisters in future radioactive waste repositories depends mainly on sulfide concentration at the boundary between groundwater and the buffer, which in turn depends on SRB growth conditions (e.g., sulfate accessibility, carbon availability and electron donors) and geochemical parameters (e.g., presence of ferrous iron, which immobilizes sulfide). Maintaining high bentonite density is also important in mitigating canister corrosion. Significance and Impact of the Study: The sulfide diffusion coefficients can be used in safety calculations regarding waste canister corrosion. The work supports findings that microbial activity in compacted bentonite will be restricted. The study emphasizes the importance of growth conditions for sulfate reduction at the groundwater boundary of the bentonite buffer and linked sulfide production.     

PHOTOSYNTHETIC ADAPTATION OF A BLOOM‐FORMING CYANOBACTERIUM MICROCYSTIS AERUGINOSA (CYANOPHYCEAE) TO PROLONGED UV‐B EXPOSURE1

The bloom‐forming cyanobacterium Microcystis aeruginosa Kütz 854 was cultured with 1.05 W·m^?2 UV‐B for 3 h every day, and its growth, pigments, and photosynthesis were investigated. The specific growth rates represented by chl a concentration and OD₇₅₀ were inhibited 8% and 9% by UV‐B exposure, respectively. Six days of UV‐B treatment significantly reduced cellular contents of phycocyanin and allophycocyanin by 32% and 62%, respectively, and markedly increased the carotenoid content by 27%, but had little effect on the chl a content. The initial values of optimal photosynthetic efficiency for UV‐B treated samples were, respectively, 52%, 87%, and 93% of controls on days 4, 7, and 10 of growth. The light‐saturated photosynthetic rates at day 6 were significantly lower than controls grown without UV‐B. The probability of electron transfer beyond Q_A decreased during UV‐B exposure, and this indicated that the acceptor side of PSII was one of main damage sites. The adaptation of M. aeruginosa 854 to UV‐B radiation could be observed from light‐saturated photosynthetic rates on day 13 and diurnal changes of chl fluorescence during the late growth phase. When both exposed to higher UV‐B, samples cultured under 1.05 W·m^?2 UV‐B for 9 days recovered faster than controls. It is suggested that M. aeruginosa 854 had at least three adaptive strategies to cope with the enhanced UV‐B: increasing the synthesis of carotenoids to counteract reactive oxidants caused by UV‐B exposure, degrading phycocyanin and allophycocyanin to avoid further damage to DNA and reaction centers, and enhancing the repair of UV‐B induced damage to the photosynthetic apparatus.     

Production rate estimation of mycosporine‐like amino acids in two Arctic melt ponds by stable isotope probing with NAH13CO3

The net carbon uptake rate and net production rate of mycosporine‐like amino acids (MAAs) were measured in phytoplankton from 2 different melt ponds (MPs; closed and open type pond) in the western Arctic Ocean using a ¹³C stable isotope tracer technique. The Research Vessel Araon visited ice‐covered western‐central basins situated at 82°N and 173°E in the summer of 2012, when Arctic sea ice declined to a record minimum. The average net carbon uptake rate of the phytoplankton in polycarbonate (PC) bottles in the closed MP was 3.24 mg C · m^?3 · h^?1 (SD = ±1.12 mg C · m^?3 · h^?1), while that in the open MP was 1.3 mg C · m^?3 · h^?1 (SD = ±0.05 mg C · m^?3 · h^?1). The net production rate of total MAAs in incubated PC bottles was highest (1.44 (SD = ±0.24) ng C · L^?1 · h^?1) in the open MP and lowest (0.05 (SD = ±0.003) ng C · L^?1 · h^?1) in the closed MP. The net production rate of shinorine and palythine in incubated PC bottles at the open MP presented significantly high values 0.76 (SD = ±0.12) ng C · L^?1 · h^?1and 0.53 (SD = ±0.06) ng C · L^?1 · h^?1. Our results showed that high net production rate of MAAs in the open MP was enhanced by a combination of osmotic and UVR stress and that in situ net production rates of individual MAA can be determined using ¹³C tracer in MPs in Arctic sea ice.     

The inhibitory effects of UV-B radiation (280–315 nm) on Gunnera magellanica growth correlate with increased DNA damage but not with oxidative damage to lipids

Damage to DNA and disruption of membrane integrity by lipid peroxidation processes are two of the proposed causes of UV‐B‐induced growth inhibition in plants. However, the relative significance of these different types of molecular damage has not been established in experiments carried out under realistic physiological conditions. Plants of Gunnera magellanica (a native herb from southern Patagonia) were exposed to a gradient of biologically effective UV‐B doses (from 0 to 6.5 kJ m^?2 d^?1 of UV‐B_be) in a greenhouse study. Leaf expansion was measured and sensitive techniques were used to detect damage to DNA (in the form of cyclobutane pyrimidine dimers; CPDs) and lipid peroxidation (via electronic‐paramagnetic resonance; EPR). Leaf expansion decreased and the CPD density increased with increasing UV‐B doses, but the degree of lipid peroxidation remained unaffected. The highest UV‐B dose induced a transient oxidative stress situation (as evaluated using the ratio of ascorbyl radical to ascorbate, A^·/AH^–), which was rapidly controlled by an increase in the ascorbate pool. The present results suggest that under a range of UV‐B_be doses that overlaps the range of doses that G. magellanica plants experience in their natural environment, growth inhibition is better explained by DNA damage than by increased lipid peroxidation.     

Effect of the proton motive force inhibitor carbonyl cyanide‐m‐chlorophenylhydrazone (CCCP) on Pseudomonas aeruginosa biofilm development

Aims: Proton motive force (PMF) inhibition enhances the intracellular accumulation of autoinducers possibly interfering with biofilm formation. We evaluated the effect of the PMF inhibitor carbonyl cyanide‐m‐chlorophenylhydrazone (CCCP) on Pseudomonas aeruginosa biofilm development. Methods and Results: Four epidemiologically unrelated P. aeruginosa isolates were studied. A MexAB‐oprM overproducing strain was used as control. Expression of gene mexB was examined and biofilm formation after incubation with 0, 12·5 and 25 μmol l^?1 of CCCP was investigated. Mean values of optical density were analysed with one‐way analysis of variance and t‐test. Two isolates subexpressed mexB gene and only 25 μmol l^?1 of CCCP affected biofilm formation. Biofilms of the other two isolates and control strain PA140 exhibited significantly lower absorbance (P ranging from <0·01 to <0·05) with either 12·5 or 25 μmol l^?1 of CCCP. Conclusions: The PMF inhibitor CCCP effect was correlated with the expression of MexAB‐OprM efflux system and found to compromise biofilm formation in P. aeruginosa. Significance and Impact of the Study: These data suggest that inhibition of PMF‐dependent trasporters might decrease biofilm formation in P. aeruginosa.