Can results from limnocorral experiments be transferred to in situ conditions?

In 1982–1984 eight limnocorral (LC) experiments, each lasting for two weeks, were performed in mesotrophic Lake Lucerne, Switzerland, to study the effects of biomanipulation (removal of crustaceans by 95 µm filter nets) on zooplankton — phytoplankton relationships and epilimnetic carbon and phosphorus fluxes. Seston concentrations and to a lesser extent primary production rates were reduced in control LCs through zooplankton grazing, and settling flux increased through fecal pellet production. But C and P regeneration were not significantly affected.We found several indications that the LCs, despite of their large size ( 70 m³, 3 m in diameter and 11 m long) were artificial systems when compared to the surrounding lake: The eddy diffusion was diminished by about one order of magnitude, nutrients depleted (but phosphorus was supplied to the LCs), the phyto- and zooplankton showed lower standing crops in the control LCs than in the lake, the phytoplankton showed a shift from nannoplankton to netplankton, the crustacean zooplankton was mostly limited in their vertical migration, and the POC and PP sedimentation rates were increased. Moreover, in our set of experiments we always found outliers, which may have been caused by the different in situ conditions at the beginning of the experiments, and further enhanced by the complexity of the enclosed system.The problems of the LC-technique, such as replicability, scaling (size and time) and data extrapolation are discussed. The impact of crustacean zooplankton on particulate matter, i.e. seston reduction and sedimentation enhancement, can be extrapolated on a qualitative rather than on a quantitative basis for the Lake Lucerne ecosystem.     

The role of plankton, zoobenthos, and sediment in organic matter degradation in oligotrophic and eutrophic mountain lakes

Intensity of organic matter degradation, assessed by the respiratory electron transport system (ETS) activity, was studied in microplankton, zooplankton, chironomid larvae as the dominant group of the macrobenthos, and sediment in mountain lakes of different trophic levels in summer months. The highest ETS activities per unit of surface were observed in sediments. Significantly lower activities were observed in microplankton, and lower still in zooplankton, and chironomids. The total ETS activity m^–2 was higher in eutrophic lakes (Jezero na Planini pri Jezeru and Krnsko jezero) than in oligotrophic ones (Zgornje Kriko jezero, Spodnje Kriko jezero, Jezero v Ledvicah). The contributions of communities investigated to total ETS activity m^–2 differed between lakes of different trophic level. Estimation of respiratory carbon loss through different components revealed that the most of the organic matter was oxidized in sediments of mountain lakes. The respiratory carbon losses were higher through zooplankton than through microplankton in all lakes. Carbon losses through plankton components and sediments were significantly lower in oligotrophic than in eutrophic lakes. The contribution of respiratory carbon loss through chironomids to total carbon loss m^–2 was higher in oligotrophic than in eutrophic lakes. Therefore, it seems that contributions of microplankton and zooplankton to mineralization processes increase, and contributions of chironomids and sediment surface decrease with increasing trophic level of the lakes.     

The effect of herbivorous crustacean zooplankton on epilimnetic carbon and phosphorus cycling

Plastic limnocorrals (LCs; volume 70 m³) in oligo-mesotrophic Lake Lucerne, Switzerland were used to manipulate planktonic communities by (1) removing large zooplankton at the start of the experiment, and (2) adding phosphate during experiments of two weeks duration.Primary production (¹⁴C-assimilation), chlorophyll, standing crops and sedimentation of particulate organic carbon (POC) and of particulate phosphorus, as well as plankton composition were assessed simultaneously in two to four differently treated LCs. Carbon and phosphorus mass balances were calculated from assimilation, temporal change in standing crop of particulate matter, and sedimentation.A quick elimination of crustaceans by screening hardly increased primary production, but decreased sedimentation and mineralisation of particulate organic carbon, and thus significantly enhanced the standing crop of POC, but decreased POC turnover. The exclusion of crustaceans increased the mean residence time of total phosphorus by a reduced P loss by sedimentation.Increased grazing pressure during the experiment showed little grazing induced effect on plankton composition and primary production except at the very end.We conclude that in an oligo-mesotrophic lake, buffering mechanisms attenuate the impact of changing grazing pressures on primary production.     

Measurement of one-bond 1Hα-13Cα couplings in backbone-labelled proteins

NMR dipole-dipole couplings between protein backbone nuclei (¹H, ¹³C, ¹⁵N, ¹H^N,¹³C) offer enormous scope for the rapid determination of protein global folds. Here, we show that measurement of one-bond splittings in the protein backbone is facilitated by use of protein that is selectively isotopically enriched only in the backbone atoms. In particular, ¹H-¹³C couplings can be measured simply and with high sensitivity by use of conventional heteronuclear single quantum correlation (HSQC) techniques.     

5-Fluorotryptophan-Containing N-Terminal Domain of the α-Subunit of the Torpedo californica Acetylcholine Receptor: Preparation in Escherichia coli and 19F NMR Study

A protein corresponding to the extracellular 1–209 domain of the -subunit of the nicotine acetylcholine receptor from the electric organ of Torpedo californica was prepared using the corresponding cDNA domain by culturing Escherichia coli cells on a synthetic medium supplemented with 5-fluoro-L-tryptophan. The presence of a (His)₆ fragment preceding the 1–209 sequence allowed purification of the protein isolated from inclusion bodies by affinity chromatography on Ni-NTA Agarose. The incorporation of 5-fluorotryptophan residues was found by ¹⁹F NMR to be 50%. The spectrum of the protein reduced in the denaturing conditions and subsequently reoxidized in a dilute solution under denaturing conditions in the presence of 0.05% SDS was sufficiently resolved, which allowed partial assignment of ¹⁹F resonances using the Trp60Phe mutant protein. The ability of the prepared domains to specifically bind snake -neurotoxins was demonstrated with the use of radioiodinated -bungarotoxin and trifluoroacetylated -cobratoxin.     

Tunneling Processes Induced by Terahertz Electric Fields

Tunneling processes induced by terahertz frequency electric fields havebeen investigated.A drastic enhancement of the tunneling probabilityhas been observed by increasing the frequency at_e 1 where_e is the tunneling time.For a given constant tunneling rate an increase offrequency by a factor of seven leads to a drop of the requiredelectric field strengthby three orders of magnitude.It is shown that the enhancement of tunneling ionization at terahertz frequencies is due to the factthat electrons can absorb energy from the radiation field during tunnelingreducing the effective width of the tunneling barrier.     

Heterogeneity of the α-globin gene defects in German α-thalassemia affected families

Summary Analysis of -thalassemia syndromes in several German families revealed DNA deletion as well as nondeletion forms as the molecular basis for the defects. Thus, the -thalassemia haplotype was identified as the (–)^3.7 rightward deletion form, and the region of the putative recombination process generating such a deletion was further characterized. In addition three different ° haplotypes, (--)^MED, (--)^>26, and ()^T, could be detected using -and -globin gene-specific probes.     

Effects of zooplankton on sedimentation in pelagic ecosystems: Theory and test in two lakes of the Canadian shield

A simple heuristic theory based on conservation of matter and describing the fate of autotrophic production in pelagic ecosystems was developed to assist in conceptualizing how zooplankton affect sedimentation processes in lakes and oceans. The theory predicted that effects of zooplankton on the fraction of autotrophic incorporation that sediments (the export ratio) will be a function of factors related both to zooplankton digestion and egestion and to tendencies of particulate matter to sediment directly prior to mineralization. As a result, effects of zooplankton grazing on the export ratio were predicted to be site-dependent, a function of physical conditions and zooplankton communities characterizing an ecosystem. The theory was tested by monitoring autotrophic production of C, N, and P, sedimentation of C, N, and P, and zooplankton biomass in two lakes of the Canadian shield characterized by contrasting morphometry and food-web structure. In Lake 110, a small elongate lake protected from wind exposure, export ratios of C, N, and P declined strongly with zooplankton biomass. In contrast, in L240, a larger lake with considerably greater wind exposure, export ratios increased with zooplankton biomass. These results were consistent with predictions of our theory that effects of zooplankton on sedimentation processes will depend on the tendency of particulate matter to directly sediment relative to the tendency of egested materials to sediment. However, no significant differences in relationships between export ratios for C, N, and P and zooplankton biomass were found.     

A bloom of Dunaliella parva in the Dead Sea in 1992: biological and biogeochemical aspects

A bloom of the unicellular green alga Dunaliella parva (up to 15 000 cells m1^–1) developed in the upper 5 m of the water column of the Dead Sea in May-June 1992. This was the first mass development of Dunaliella observed in the lake since 1980, when another bloom was reported (up to 8800 cells m1^–1). For a bloom of Dunaliella to develop in the Dead Sea, two conditions must be fulfilled: the salinity of the upper water layers must become sufficiently low as a result of dilution with rain floods, and phosphate must be available. During the period 1983–1991 the lake was holomictic, hardly any dilution with rainwater occurred, and no Dunaliella cells were observed. Heavy rain floods in the winter of 1991–1992 caused a new stratification, in which the upper 5 m of the water column became diluted to about 70% of their former salinity. Measurements of the isotopic composition of inorganic carbon in the upper water layer during the bloom (¹³C = 5.1) indicate a strong fractionation when compared with the estimated –3.4 prior to the bloom. The particulate organic carbon formed was highly enriched in light carbon isotopes ( ¹³ C = – 13.5). The algal bloom rapidly declined during the months June–July, probably as a result of the formation of resting stages, which sank to the bloom. A smaller secondary bloom (up to 1850 cells m1–1) developed between 6 and 10 m depth at the end of the summer. Salinity values at this deep chlorophyll maximum were much beyond those conductive for the growth of Dunaliella, and the factors responsible for the development of this bloom are still unclear.     

Distribution and composition of particulate organic matter in the Ross Sea (Antarctica)

The biochemical composition and spatial distribution of particulate organic matter (POM) were studied in the Ross Sea (Antarctica) in summer 1989 to assess the quantitative role of organic carbon fractions in the cycling of organic matter in the water column. Large differences in chemical composition were observed between surface and deep layers. The results indicated that, despite large geographical differences, POM was quite homogeneous, of phytoplankton origin and mostly detrital. Different ratios were used to investigate the changes in biochemical composition of particulate organic matter in relation to the ice-melting: CN (organic carbonorganic nitrogen ratio) and C-POMPOC (sum of carbohydrate, protein and lipid carbontotal organic carbon ratio) were used to analyse the percentage of refractory organic material. PPRTPCHO (proteincarbohydrate ratio) were used to establish POM age and RNADNA ratios as a relative measure of particulate activity; POCChl a and N-PPRTChl a ratios were used to estimate the autotrophic contribution to the suspended particulate organic matter. Despite its low caloric value (5.3 Kcal g POM^–1), an high caloric content in the photic layer (1.6 Kcal m^–3 of POM and 2.5 Kcal m^–3 of POC) was found thus indicating that a large amount of food was available to higher trophic levels.     

Seasonal and annual dynamics of particulate carbon flux in the Barents Sea

Mathematical modelling was used to explore the seasonal and annual variability of primary, new and secondary production as well as sedimentation between 72° and 80°N in the central Barents Sea during the years 1981 to 1983. 1981 and 1982 were years with extensive ice coverage while 1983 experienced little sea-ice. The phytoplankton spring bloom started usually in April/May at about 75°N and was delayed from May/June in the south to August/September in the north as a function of thermal stratification and sea-ice dynamics. The model indicates that several, simultaneous spring bloom events, separated in space, can be found, especially during years with low ice coverage. The annual estimates of primary production, secondary production and sedimentation decreased on average from 73, 7.3 and 48 to 18, 1.8 and 9 g C m^–2 year^–1 between the southern and the northern part of the Barents Sea respectively. The annual estimates of particulate carbon flux were much higher in 1983 compared to 1981–1982, especially in the north where up to 6 times higher rates were calculated for 1983. The number of zooplankton species present in spring in the southern Barents Sea is governed by over-wintering success, but probably also influenced by advection of Atlantic water. The model was run for Atlantic water with 10,000, 3,000 or none copepods per m² present in March, indicating that sedimentation can vary between 38 and 61 g C m^–2 year^–1 due to zooplankton grazing alone. This suggests that the supply of organic carbon to the aphotic zone of the Barents Sea is only partly determined by the strength and duration of phytoplankton blooms, but strongly influenced by zooplankton dynamics.     

Measurement of the protein backbone dihedral angle φ based on quantification of remote CSA/DD interference in inter-residue 13C′(i − 1)-13Cα(i) multiple-quantum coherences

A novel triple-resonance NMR method is presented for the measurement of the protein backbone dihedral angle based on differential multiple-quantum relaxation induced by relaxation interference between ¹H(i)-¹³C(i) dipolar and ¹³C(i–1) (carbonyl) chemical shift anisotropy mechanisms. The method employs a simultaneous transfer of ¹⁵N magnetization to the inter- and intra-residue ¹³C carbons as well as the directly attached carbonyl carbon ¹³C. Results obtained on ¹³C,¹⁵N-labeled ubiquitin demonstrate the potential of the method.     

Kinetic changes of αB crystallin expression in neoplastic cells and syngeneic rat fibroblasts at various subculture stages

B crystallin, a structural protein of the mammalian lens essential for the maintenance of lens transparency, is also expressed, at variable levels, in many extraocular tissues where it plays a protective role in stress conditions. In fact, heat or toxic shocks, as well as pathological states, increase B crystallin levels in many cell types. Here we show that B crystallin expression is also modulated in subcultures of rat fibroblasts and Galliera sarcoma cells. Western blots analysis with anti B crystallin antibodies reveals the presence of the protein in both cell populations, although the kinetic pattern of expression is different. Galliera fibroblasts constitutively express the protein up to the 70th subculture and afterwards the synthesis ceases. On the other hand, Galliera sarcoma cells do not contain B crystallin in the early stages of the culture, but there is a progressive increases between the 20th and 40th cell subculture. Differences also exist concerning the intracellular distribution: B crystallin is diffusely localized in the cytoplasm of fibroblasts while in sarcoma cells it localizes mainly to the perinuclear region. B crystallin is totally recovered as soluble protein in the supernatants obtained after low speed centrifugation of fibroblast homogenates, while in sarcoma cells a portion of the protein is also recovered in the insoluble pellet. Intracellular pH measurements show an alkaline cytosol in sarcoma cells compared to fibroblasts. Heat shock treatment of fibroblast subcultures constitutively expressing B crystallin induces an over-expression of the protein, while in fibroblasts whose biosynthetic capacity is lost, heat shock is unable to activate the crystallin gene. Correlation between B crystallin expression and proliferative rate shows that highly proliferating fibroblasts do not express B crystallin, while neoplastic cells do.     

Emission of gaseous nitrogen oxides from an extensively managed grassland in NE Bavaria, Germany.

We analysed the stable isotope composition of emitted N₂O in a one-year field experiment (June 1998 to April 1999) in unfertilized controls, and after adding nitrogen by applying slurry or mineral N (calcium ammonium nitrate). Emitted N₂O was analysed every 2–4 weeks, with additional daily sampling for 10 days after each fertilizer application. In supplementary soil incubations, the isotopic composition of N₂O was measured under defined conditions, favouring either denitrification or nitrification. Soil incubated for 48 h under conditions favouring nitrification emitted very little N₂O (0.024 mol g_dw ^–1) and still produced N₂O from denitrification. Under denitrifying incubation conditions, much more N₂O was formed (0.91 mol g_dw ^–1 after 48 h). The isotope ratios of N₂O emitted from denitrification stabilized at ¹⁵N = –40.8 ± 5.7 and ¹⁸O = 2.7 ± 6.3. In the field experiment, the N₂O isotope data showed no clear seasonal trends or treatment effects. Annual means weighted by time and emission rate were ¹⁵N = –8.6 and ¹⁸O = 34.7 after slurry application, ¹⁵N = –4.6 and ¹⁸O = 24.0 after mineral fertilizer application and ¹⁵N = –6.4 and ¹⁸O = 35.6 in the control plots, respectively. So, in all treatments the emitted N₂O was ¹⁵N-depleted compared to ambient air N₂O (¹⁵N = 11.4 ± 11.6, ¹⁸O = 36.9 ± 10.7). Isotope analyses of the emitted N₂O under field conditions per se allowed no unequivocal identification of the main N₂O producing process. However, additional data on soil conditions and from laboratory experiments point to denitrification as the predominant N₂O source. We concluded (1) that the isotope ratios of N₂O emitted from the field soil were not only influenced by the source processes, but also by microbial reduction of N₂O to N₂ and (2) that N₂O emission rates had to exceed 3.4 mol N₂O m^–2 h^–1 to obtain reliable N₂O isotope data.     

Autotrophic carbon sources for heterotrophic bacterioplankton in a floodplain lake of central Amazon

The relative contribution of autotrophic carbon sources (aquatic macrophytes, flooded forest, phytoplankton) for heterotrophic bacterioplankton was evaluated in a floodplain lake of the Central Amazon. Stable carbon isotopes (¹³C) were used as tracers. Values of ¹³C of different autotrophic sources were compared to those of dissolved organic carbon (DOC) and those of bacterially produced CO₂.The percentage of carbon derived from C₄ macrophytes for bacterially produced CO₂ was the highest, on average 89%. The average ¹³C value of CO₂ from bacterial respiration was –18.5 ± 3.3. Considering a fractionation of CO₂ of 3 by bacterial respiration, ¹³C value was –15.5, near C₄ macrophyte ¹³C value (–13.1).The average value of total DOC ¹³C was –26.8 ± 2.4. The percentage of C₄ macrophytes carbon for total DOC was on average 17%. Considering that bacteria consume mainly carbon from macrophytes, the dominance of C₃ plants for total DOC probably reflects a faster consumption of the former source, rather than a major contribution of the latter source.Heterotrophic bacterioplankton in the floodplain may be an important link in the aquatic food web, transferring the carbon from C₄ macrophytes to the consumers.     

Protein biosynthetic capacity in the endosperm tissue of ripening castor bean seeds

Endosperm tissue was excised from Ricinus communis plants at different stages during seed maturation. The various stages were characterized on the basis of total RNA, protein and lipid content. Polyadenylated RNA was recovered from the total RNA by affinity chromatography on oligo(dT)cellulose. With the exception of that isolated from dry seeds, this poly(A⁺) RNA actively programmed protein synthesis in cell-free systems containing either wheat germ S30 extracts or nuclease treated rabbit reticulocyte lysates at each developmental stage examined. Translational products were separated electrophoretically and were visualized by fluorography. The capacity to synthesize protein was also estimated during in vivo labelling studies. Developmental changes in the capacity of maturing endosperm tissue to synthesize a characteristic protein, R. communis agglutinin, were followed by immunoprecipitating this protein from the total in vitro products synthesized at various stages. Endoplasmic reticulum membranes were isolated from maturing endosperm tissue by sucrose density gradient centrifugation. The role of the endoplasmic reticulum (ER) in protein glycosylation was indicated by (a) localizing the enzymes catalysing the incorporation of N-acetylglucosamine and mannose into mono- and oligosaccharide lipid and into glycoprotein, (b) localizing particulate ³H-labelled glycoprotein amongst cellular fractions prepared from endosperm tissue which had been incubated with [³H]N-acetylglucosamine.Abbreviations polyCA⁺)RNA polyadenylated RNA - SDS sodiumdodecylsulphate - TCA trichloroacetic acid - RCA₁₂₀ Ricinus communis agglutinin, type I - NP40 Nonidet P40 - PMSF phenylmethylsulphonyl fluoride     

Short-term variations in particulate matter sedimentation off Kapp Norvegia,Weddell Sea,Antarctica: relation to water mass advection,ice cover,plankton biomass and feeding activity

Summary A multi-cup sediment trap was deployed at 250m in the shelf area off Kapp Norvegia, Weddell Sea (630 m water depth) to determine the relative importance of water mass advection, sea ice movement, phytoplankton biomass and plankton feeding. Short-term fluctuations in sedimentation were determined using a sampling frequency of 2.7 days over 54 days during January and February 1988. Three periods of enhanced sedimentation were associated with water mass exchange, settling of diatoms following break-up of ice cover and release of fecal matter by krill feeding on particulate matter derived from phytoplankton and ice algae. An initial sedimentation pulse (28 Jan) was mainly due to sinking pelagic diatoms and krill fecal strings containing algae released from sea ice passing over the trap position. The ¹³C-composition of the sedimented organic carbon was about-24. The isotope ratio decreased sharply by about 5.5 at the end of the first pulse indicating the source of sinking matter becoming pelagic diatoms of the retreating ice-edge. At this time the diatom Corethron criophilum contributed a very high proportion of the organic flux causing an increase of the opal/C_org ratios. The second pulse (6 Feb) was due to empty diatom frustules, minipellets and small planktonic aggregates. Much of the organic carbon was transported by round fecal pellets. During the third pulse (14 Feb), round fecal pellets transported even more; the percentage of C. criophilum to the diatom organic carbon flux was more than 80% (>2mg C m^–2 day^–1).Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

The ‘shock period’: dynamics of phytoplankton during the spring–summer transition of a stratifying English lake

The spring to summer transition in a productive English lake is considered with respect to phytoplankton and its environmental conditions. Salient environmental changes include the onset of temperature/density stratification that is usually accompanied by a clear-water phase associated with a maximum of grazing Daphnia and a minimum of phytoplankton in the 0â€5 m zone. Below this zone, as thermal stratification progresses, a deep maximum of phytoplankton can develop under strong thermal/density gradients and enhanced light penetration. Examples are resolved by estimations of chlorophyll-a , beam attenuance in situ and cell counts. Attributed origins are by sedimentation of diatoms, migration of flagellates, and depth-adjusted buoyancy of a gas-vacuolate cyanophyte. The transition period involves a decline of spring-associated diatom populations and a rise of summer-associated species. The generally low algal abundance within the transition phase has at least four origins †prior nutrient (Si) depletion, sedimentation, grazing, and low inoculum levels of successor species. It can be augmented by the re-growth of species abundant in spring, by early extensions of normally summer species, by seasonally characteristic colonial chrysophytes, and by other phytoflagellates of small size that are seasonally less specific (opportunistic) and probably critical for Daphnia grazing with consequent generation of the clear-water phase.     

Photosynthetic formation of inorganic pyrophosphate in phototrophic bacteria

In this paper we report studies on photosynthetic formation of inorganic pyrophosphate (PP_i) in three phototrophic bacteria. Formation of PP_i was found in chromatophores from Rhodopseudomonas viridis but not in chromatophores from Rhodopseudomonas blastica and Rhodobacter capsulatus. The maximal rate of PP_i synthesis in Rps. viridis was 0.15 mol PP_i formed/(min*mol Bacteriochlorophyll) at 23°C. The synthesis of PP_i was inhibited by electron transport inhibitors, uncouplers and fluoride, but was insensitive to oligomycin and venturicidin. The steady state rate of PP_i synthesis under continuous illumination was about 15% of the steady-state rate of ATP synthesis. The synthesis of PP_i after short light flashes was also studied. The yield of PP_i after a single 1 ms flash was equivalent to approximately 1 mol PP_i/500 mol Bacteriochlorophyll. In Rps. viridis chromatophores, PP_i was also found to induce a membrane potential, which was sensitive to carbonyl cyanide p-trifluoromethoxyphenylhydrazone and NaF.Abbreviations BChl Bacteriochlorophyll - F₀F₁-ATPase Membrane bound proton translocating ATP synthase - FCCP Carbonyl cyanide p-trifluoromethoxyphenylhydrazone - H⁺-PPase Membrane bound proton translocating PP_i synthase - TPP⁺ Tetraphenyl phosphonium ion - TPB^- Tetraphenyl boron ion - Transmembrane electrical potential difference     

Zooplankton community changes in Lake Kinneret (Israel) during 1969–1985

Long-term records (1969–1985) of zooplankton density in Lake Kinneret indicated significant reduction of biomass (Copepods, Cladocera, Rotifera) and production (Copepods, Cladocera). Nauplius and adult copepod densities decreased but those of copepodites did not change. Mesocyclops was suppressed more than the smaller Thermocyclops and males of both genera became more abundant relative to the larger females. Ratios of small/large Cladocera densities became higher. Numbers of total cladocerans were stable, and therefore reduction of Cladocera grazing capacity is assumed. The abundant Keratella spp. were reduced. It is likely that intensification of fish visual-attack-predation pressure shifted the size-class structure towards smaller adult copepods and cladocerans. Reduction of Keratella spp. and copepod nauplii was probably affected by increasing pressure of fish filter-feeders. Data on fish food consumption, feeding behaviour and fisheries management suggested their direct impact on long-term changes of zooplankton in Lake Kinneret.