Interannual variability of phytoplankton productivity and related parameters in Lake Constance: no response to decreased phosphorus loading?

In meso-eutrophic Lake Constance (Germany-Austria-Switzerland),phytoplankton bioraass, pigments and water transparency, aswell as primary productivity, have been followed between 1980and 1989. During this period, municipal phosphorus loading declinedsignificantly. Since 1981, soluble reactive phosphorus (SRP)concentrations during deep lake mixing have decreased from 3.0to currently 1 6 mmol m^–3 at a rate of 7% year^–1.Nitrate concentrations, by contrast, continued to rise. Duringthe period of maximum phosphorus loading, flushing through theoutlet and sedimentation were about equally important sinksof phosphorus from the euphotic zone. Recently, however, sedimentationand subsequent burial of P in the bottom deposits contributedabout three-quarters to the overall P-losses from the systemMain reasons for this shift are unchanged settling fluxes ofphosphorus out of the euphotic zone and decreasing concentrationsof total phosphorus in the water. Only during spring, do concentrations of soluble reactive phosphoruswithin the euphotic zone decrease in proportion to the formationof particulate organic matter. Later during the season, euphoticSRP concentrations continue to be low but are no longer matchedby high plankton biomass because phosphorus is efficiently removedby settling of particles In spite of the observed dramatic decreasein phosphorus loading since 1980, chlorophyll concentrationsand water transparency, as well as annual phytoplankton productivity(300 g C m^–2), have not shown a consistent downward trend.However, the intensity of phosphorus regeneration within theeuphoric zone, which can be used as a measure of the degreeof nutrient limitation, is likely to have increased significantlyThe most probable explanation for the insensitivity of importanttrophic state indicators to reduced nutrient loading is that,in Lake Constance, biomass accumulation to a greater extentis controlled by losses, mainly grazing by zooplankton and sedimentation,than by primary resources. This is concluded from the observationthat phytoplankton biomass always falls far short of the nutrient-dependentcarrying capacity of the system.     

Internal seiches in Lake Constance: influence on plankton abundance at a fixed sampling site

During thermal stratification, pronounced internal seiches occurin Lake Constance with periods of 4–6 days The amplitudesreach 12 m at the sampling site in berlinger See (northwesternpart of Lake Constance). Seiches change the thickness of thewarm and generally biologically rich epilimnion and, thus, alsothe areal abundance of planktonic organisms at a fixed samplingsite. The potential impact of seiche-dnven changes of epilimneticthickness on observed plankton abundance was calculated usingcontinuously recorded temperature profiles and weekly verticalprofiles of plankton biomass. Observed plankton biomass wasrecalculated by taking into account the effect of changing layerthickness in order to give a more realistic picture of biomasschanges caused by waxing and waning of populations Our calculationsimply that changes of strata thickness do not mask the generalseasonal trend in population dynamics (e g. spring bloom andclear water phase), estimates of average yearly standing stockare not significantly affected if sampling is done at leastweekly. However, changes of strata thickness can alter arealplankton abundance at the sampling site by a factor of 2 within2 days During pronounced seiches, areal abundance of phytoplankton,which generally exhibit a stronger vertical gradient than-mostother plankton, may be changed by a factor of 3–4 withinhours Hence, at our sampling site, the impact of changes instrata thickness cannot be ignored for detailed analysis ofpopulation dynamics of autotrophs involving comparisons betweensingle observations     

High-level expression of a tobacco chitinase gene in Nicotiana sylvestris. Susceptibility of transgenic plants to Cercospora nicotianae infection

Endochitinases (E.C. 3.2.14, chitinase) are believed to be important in the biochemical defense of plants against chitin-containing fungal pathogens. We introduced a gene for class I (basic) tobacco chitinase regulated by Cauliflower Mosaic Virus 35S-RNA expression signals into Nicotiana sylvestris. The gene was expressed to give mature, enzymatically active chitinase targeted to the intracellular compartment of leaves. Most transformants accumulated extremely high levels of chitinase-up to 120-fold that of non-transformed plants in comparable tissues. Unexpectedly, some transformants exhibited chitinase levels lower than in non-transformed plants suggesting that the transgene inhibited expression of the homologous host gene. Progeny tests indicate this effect is not permanent. High levels of chitinase in transformants did not substantially increase resistance to the chitin-containing fungus Cercospora nicotiana, which causes Frog Eye disease. Therefore class I chitinase does not appear to be the limiting factor in the defense reaction to this pathogen.     

Cryopreservation of Digitalis lanata Ehrh. cell cultures: Preculture and freeze tolerance

Cryopreservation experiments were performed with Digitalis lanata cell cultures. The main stress was laid on the behaviour of the cells during the preculture period and the capacity of various preculture additives to induce freeze tolerance. The following compounds were used as preculture additives: trehalose, mannitol, sucrose, melibiose, proline, and sorbitol. They are listed in the order of their respective efficiency. Using trehalose, high post-thaw viability rates were achieved and the cells resumed growth after a short lag period. Melibiose was used as a preculture additive for the first time. Its suitability was in the range of that of sucrose. Proline and sorbitol were not able to induce freeze tolerance in Digitalis cells. Cell viability showed a considerable decrease at the beginning of the preculture period. This reduction was found to be transient in the presence of trehalose, mannitol, sucrose, and melibiose. The damaging effects of proline and sorbitol were too severe to be compensated for by the cells. The PAL activity increased markedly in the presence of proline, whereas the trehalose-treated and the control cells behaved nearly identical to one another.     

Characterization of microcarrier cultures of neurons and astrocytes from cerebral cortex and cerebellum

In the present investigation a method is described for culturing cerebellar granule cells (glutamatergic neurons), cerebral cortical neurons (GABAergic neurons) and cortical astrocytes on Cytodex 3 microcarriers. It was possible to obtain a high yield of attached neurons and astrocytes on the microcarriers and the cell specific characteristics such as the ability to release neurotransmitter (neurons) and a high activity of glutamine synthetase (astrocytes) were preserved. This system, allowing mixtures of neurons and astrocytes at any given ratio to be produced, may constitute an attractive model system by which the interaction between neurons and astrocytes with regard to exchange of neurotransmitter precursors as well as other compounds may be studied.     

Structure elucidation of the core regions from Citrobacter O4 and O36 lipopolysaccharides by chemical and enzymatic methods, gas chromatography/mass spectrometry, and NMR spectroscopy at 500 MHz

Novel enterobacterial core oligosaccharides were isolated from Citrobacter O4 and O36 lipopolysaccharides, and their structures were determined by methylation analysis, Smith degradation and enzymatic degradations, gas chromatography/mass spectrometry, and two-dimensional phase-sensitive correlated, relayed coherence transfer, double-quantum, triple-quantum-filtered, and nuclear Overhauser effect (NOE) 1H NMR spectroscopy at 500 MHz. In the formulas, all hexose residues are D-hexopyranoses, and heptoses are L-glycero-D-manno-heptopyranoses; the alternative locations of the side-chain heptose and pyrophosphorylethanolamine (PPEtN) residues are marked by dashed lines; dOclA stands for 3-deoxy-D-manno-octulosonic acid. (formula; see text) Along with these complete cores, incomplete ones, lacking the hexosamine trisaccharides, occur in the lipopolysaccharides of both types. Qualitative NOE data were in good agreement with the minimum energy conformation of the above O36 oligosaccharide, calculated with the aid of the SUGAR program [Sundin, A., Carter, R. E., & Liljefors, T. (1988) J. Mol. Graphics (in press)].     

Structure elucidation of the core octasaccharide from Citrobacter PCM 1487 with the aid of 500-MHz, two-dimensional phase-sensitive correlated, relayed-coherence transfer, double-quantum, triple-quantum filtered, and N.O.E. H-n.m.r. spectra

The main features of the primary structure of the octasaccharide, - -Glcp-(1→2)-- -Glcp-(1→2)-[- -GalpNAc- (1→3)]-- -Galp-(1→3)-- -Glcp-(1→3)-[- -Hepp-(1→7)]-- -Hepp-(1→3)-- -Hep, have been determined in the ab initio manner by ¹H-n.m.r. spectroscopy without resorting to biochemical methods of analysis. Several nontypical interresidue n.O.e. values point to a preferred solution conformation of the molecule.     

Complete 1H-NMR spectral assignments for globotriaosyl-Z- and isoglobotriaosyl-E-ceramide

Two-dimensional scalar-correlated (COSY) 1H-NMR spectra of the title compounds, and phase-sensitive COSY spectrum of lactosylceramide, have been fully assigned and some spectral reassignments for related structures suggested. Glycosylation-induced shifts, and shielding by Z- and E-ceramide residues are discussed.     

Molecular cloning of the c2 locus of Zea mays, the gene coding for chalcone synthase

Summary The c2 locus of Zea mays, identified as one of the genes affecting anthocyanin biosynthesis, was cloned using the transposable element En (Spm) as a gene tag. The Spm element present at the c2 locus in the autonomously mutating c2-m1 line was isolated using En1 element specific probes. Sequences flanking the element were identified as c2 locus specific and were used to clone the nonautonomous c2-m2 and wild-type alleles. The cloning and analysis of a cDNA complementary to the c2 locus provided evidence that this gene encodes the enzyme chalcone synthase.