Showing papers by "Leibniz Association published in 1999"

Sequence and analysis of chromosome 4 of the plant Arabidopsis thaliana

Abstract: The higher plant Arabidopsis thaliana (Arabidopsis) is an important model for identifying plant genes and determining their function. To assist biological investigations and to define chromosome structure, a coordinated effort to sequence the Arabidopsis genome was initiated in late 1996. Here we report one of the first milestones of this project, the sequence of chromosome 4. Analysis of 17.38 megabases of unique sequence, representing about 17% of the genome, reveals 3,744 protein coding genes, 81 transfer RNAs and numerous repeat elements. Heterochromatic regions surrounding the putative centromere, which has not yet been completely sequenced, are characterized by an increased frequency of a variety of repeats, new repeats, reduced recombination, lowered gene density and lowered gene expression. Roughly 60% of the predicted protein-coding genes have been functionally characterized on the basis of their homology to known genes. Many genes encode predicted proteins that are homologous to human and Caenorhabditis elegans proteins.

Microphysical particle parameters from extinction and backscatter lidar data by inversion with regularization: simulation.

Abstract: A method is proposed that permits one to retrieve physical parameters of tropospheric particle size distributions, e.g., effective radius, volume, surface-area, and number concentrations, as well as the mean complex refractive index on a routine basis from backscatter and extinction coefficients at multiple wavelengths. The optical data in terms of vertical profiles are derived from multiple-wavelength lidar measurements at 355, 400, 532, 710, 800, and 1064 nm for backscatter data and 355 and 532 nm for extinction data. The algorithm is based on the concept of inversion with regularization. Regularization is performed by generalized cross-validation. This method does not require knowledge of the shape of the particle size distribution and can handle measurement errors of the order of 20%. It is shown that at least two extinction data are necessary to retrieve the particle parameters to an acceptable accuracy. Simulations with monomodal and bimodal logarithmic-normal size distributions show that it is possible to derive effective radius, volume, and surface-area concentrations to an accuracy of +/-50%, the real part of the complex refractive index to +/-0.05, and the imaginary part to +/-50%. Number concentrations may have errors larger than +/-50%.

Direct amplification of the entire ITS region from poorly preserved plant material using recombinant PCR.

Abstract: Sequences of the internal transcribed spacers (ITS) of the nuclear ribosomal DNA are important molecular markers in phylogenetic analyses. To obtain sequences from herbarium material in which DNA often is severely degraded, the ITS region has to be amplified in two steps. Two methods that reduce bench time and reagents used are described. (i) Separately amplified preparations of subunits ITS-1 and ITS-2 are combined before purification. The presence of two fragments in the sequencing reaction does not impair the quality of sequences. (ii) Newly designed internal primers amplify partly overlapping regions of the two subunits. A combination of these internal primers with the external primers in one PCR allows the amplification of the entire ITS region even when degraded DNAs are used. This recombinant PCR approach, taking into account the +A bases added by several Taq DNA polymerases, will also be useful with other marker regions used in molecular phylogenetics.

Effects of cyanobacterial toxins and aqueous crude extracts of cyanobacteria on the development of fish and amphibians

Abstract: The effects of cyanobacterial hepatotoxins microcystin-LR, -RR, and -YR, of the neurotoxins saxitoxin and anatoxin-a, and of crude aqueous extracts of cyanobacteria were determined on the embryos of fish and amphibians from cleavage up to advanced stages of embryonic development. No acute toxic effects were observed after exposure to microcystins at 0.5, 5, and 50 μg/L, but the timing of hatching was altered in rainbow trout: earlier hatching occurred with 0.5, 5, and 50 μg/L microcystin-RR, 5 and 50 μg/L microcystin-YR, and 50 μg/L microcystin-LR; a minor delay in hatching was observed at 0.5 and 5 μg/L microcystin-LR. In axolotl, a delay in feeding was observed (microcystin-LR at 5 and 50 μg/L; microcystin-YR at 50 μg/L). After termination of exposure and rearing in toxin-free tanks, survival rate and growth were adversely affected in zebrafish larvae preexposed to microcystin-LR at 5 and 50 μg/L. At the highest applied concentration of microcystin-LR (10 mg/L), morphological effects were detected. Saxitoxin at 10 μg/L and above delayed hatching in zebrafish and led to malformations and mortalities at 500 μg/L. Hatching was also delayed in axolotl at 500 μg/L saxitoxin. Anatoxin-a (400 μg/L) altered the heart rate in zebrafish, but no chronic effects were observed. Far more pronounced effects, compared to those obtained with pure toxins, were observed following exposure to various aqueous crude extracts of cyanobacteria from field samples and batch cultures: similar malformations combined with high mortalities and adverse effects on outer egg structures were observed concomitantly in all species. HPLC data showed that these effects cannot be attributed to microcystin content alone. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 77–88, 1999

Size distributions of NLC particles as determined from 3‐color observations of NLC by ground‐based lidar

Abstract: From June to August 1998 the ALOMAR Rayleigh/Mie/Raman lidar, located at 69°N and 16°E in Northern Norway, repeatedly observed noctilucent clouds (NLCs) overhead the lidar. Due to a recent upgrade in detector technology, the lidar was able to obtain 151 hours of NLC observations, simultaneously at 355, 532, and 1064 nm. For the 11 strongest NLC events, we have calculated size distributions for the NLC particles from the backscatter ratios measured at the 3 wavelengths and using the assumptions of spherical ice particles with a monomodal lognormal size distribution. For all events evaluated at the layer maxima, we obtain well-defined median radii rmed, width parameters σ, and particle number densities NNLC for the NLC particle distributions. Mean values for 10 out of the 11 events are rmed = 51 nm, σ = 1.42, and NNLC = 82 cm−3.

IL-2-deficient mice raised under germfree conditions develop delayed mild focal intestinal inflammation

Abstract: Interleukin-2 (IL-2) amplifies immune stimuli and influences B cell differentiation. IL-2-deficient mice spontaneously develop intestinal inflammation if raised under specific pathogen-free (SPF) c...

Retention of nutrients in river systems: dependence on specific runoff and hydraulic load

Abstract: The total nutrient inputs (emissions) from point and diffuse sources into 100 different river basins in Europe are compared with the measured load (transport). The catchment areas range between 121 and 194 000 km2. Other characteristic parameters of the basins, including specific runoff, surface water area and the nutrient concentration show large differences. Independent of the different methods applied for estimating nutrient emissions, these are in general higher than the actual transport. The ratio of the transport to the emission was used to exclude the effects of basin size and to facilitate comparisons between river basins. A statistical model of the retention, including net sedimentation and denitrification, is derived for the description of the discrepancy between the measured transport and the estimated total emission of nutrients, which is assumed to reflect retention of nutrients in a river system. It was found that the load-weighted retention of phosphorus is controlled practically only by the specific runoff of the basin. The load- weighted retention of nitrogen is further dependent on the proportion of the basin area occupied by surface water, the basin size itself and the mean annual nitrogen concentration at a specific monitoring station. Application of the statistical model reduces the mean deviation between the calculated emissions and the values given by different authors from about 40% to 20%.

Conversion of cucumber linoleate 13-lipoxygenase to a 9-lipoxygenating species by site-directed mutagenesis

Abstract: Multiple lipoxygenase sequence alignments and structural modeling of the enzyme/substrate interaction of the cucumber lipid body lipoxygenase suggested histidine 608 as the primary determinant of positional specificity. Replacement of this amino acid by a less-space-filling valine altered the positional specificity of this linoleate 13-lipoxygenase in favor of 9-lipoxygenation. These alterations may be explained by the fact that H608V mutation may demask the positively charged guanidino group of R758, which, in turn, may force an inverse head-to-tail orientation of the fatty acid substrate. The R758L+H608V double mutant exhibited a strongly reduced reaction rate and a random positional specificity. Trilinolein, which lacks free carboxylic groups, was oxygenated to the corresponding (13S)-hydro(pero)xy derivatives by both the wild-type enzyme and the linoleate 9-lipoxygenating H608V mutant. These data indicate the complete conversion of a linoleate 13-lipoxygenase to a 9-lipoxygenating species by a single point mutation. It is hypothesized that H608V exchange may alter the orientation of the substrate at the active site and/or its steric configuration in such a way that a stereospecific dioxygen insertion at C-9 may exclusively take place.

Classic preconditioning decreases the harmful accumulation of nitric oxide during ischemia and reperfusion in rat hearts.

Abstract: Background—The role of NO in the mechanism of preconditioning is not understood. Therefore, we studied the effect of preconditioning and subsequent ischemia/reperfusion on myocardial NO content in the presence of an NO synthase (NOS) inhibitor. Methods and Results—Isolated working rat hearts were subjected to preconditioning protocols of 3 intermittent periods of rapid pacing or no-flow ischemia of 5 minutes’ duration each followed by a test 30 minutes of global no-flow ischemia and 15 minutes of reperfusion. Test ischemia/reperfusion resulted in a deterioration of myocardial function and a considerable increase in cardiac NO content as assessed by electron spin resonance. Preconditioning improved postischemic myocardial function and markedly decreased test ischemia/reperfusion-induced NO accumulation. In the presence of 4.6 μmol/L NG-nitro-l-arginine (LNA), basal cardiac NO content decreased significantly, although test ischemia/reperfusion-induced functional deterioration and NO accumulation were not af...

Flow karyotyping and sorting of mitotic chromosomes of barley (Hordeum vulgare L.).

Abstract: A high-yield method for isolation of barley chromosomes in suspension, their analysis and sorting using flow cytometry is described. To accumulate meristem root tip cells at metaphase, actively growing roots were subjected to subsequent treatment with 2 mmol/L hydroxyurea for 18 h, 2.5 micromol/L amiprophos methyl for 2 h, and ice water (overnight). This treatment resulted in metaphase indices exceeding 50%. Synchronized root tips were fixed in 2% formaldehyde for 20 min and chromosomes were released into a lysis buffer by mechanical homogenization, producing, on average, 5 x 10(5) chromosomes from 50 root tips. The isolated chromosomes were morphologically intact and suitable for flow cytometric analysis and sorting. While it was possible to discriminate and sort only one chromosome from a barley cultivar with standard karyotype, up to three chromosomes could be sorted in translocation lines with morphologically distinct chromosomes. The purity of chromosome fractions, estimated after PRINS with primers specific for GAA microsatellites, reached 97%. PCR with chromosome-specific primers confirmed the purity and suitability of flow-sorted chromosomes for physical mapping of DNA sequences.

A Review of Predation Impact by 0+ Fish on Zooplankton in Fresh and Brackish Waters of the Temperate Northern Hemisphere

Abstract: To assess potential differences in predation impact on zooplankton communities by small (larva) and larger 0+ juvenile fish, 18 studies were reviewed from fresh water and the brackish Baltic Sea of the northern hemisphere temperate region. These case studies were performed either in the field or in mesocosm experiments. Larva stocks were found to exert only minor impact on small zooplankton species such as rotifers, copepodids and small cladocerans. In contrast, stocks of 0+ juveniles were found to have the potential to depress populations of large cladocerans and copepods, especially during late summer and autumn. However, studies where both 0+ juvenile fish consumption and zooplankton dynamics and production were exactly quantified are still very rare, and therefore final evaluation of this interaction cannot be made. In addition, papers were summarized that describe differences in morphological and physiological performance between larva and 0+ juvenile fish. The greater impact of 0+ juvenile fish on large zooplankton may be explained by their larger mouth gape and by their better developed abilities to detect and consume their prey items. However, this partly is lessened by the lower energy requirements of juvenile fish compared with identical biomasses of fish larvae, although larva bioenergetics remains only fragmentarily understood. Consequently, selective predation by fish larvae on particular small zooplankton prey may be more important than has been detected so far.

Simultaneous and common‐volume observations of noctilucent clouds and polar mesosphere summer echoes

Abstract: Joint operations of the ALOMAR Rayleigh/Mie/Raman (RMR) lidar and ALOMAR SOUSY radar (located at 69°N latitude) let us obtain a first series of simultaneous and common-volume observations of noctilucent clouds (NLC) and polar mesosphere summer echoes (PMSE). We present the results of 22 examples of simultaneous NLC and PMSE observations made during the summers 1994 until 1997. These observations show a strong correlation of NLC with PMSE and they lead us to a classification (3 types) of the observed events. Furthermore, we conclude that, in all probability, there are common causes for the two types of layers.

Ethnic German Immigration from Eastern Europe and the former Soviet Union to Germany: the Effects of Migrant Networks

Abstract: This paper employed a widely accepted theoretical concept, the ‘theory of migrant networks’ to look at the recent immigration and absorption experience of ethnic Germans (Aussiedler) from Eastern Europe and the former Soviet Union in Germany. Consistent with network theory, the social background of the Aussiedler group became more representative of the sending communities as migrant networks expanded. The paper additionally showed that Aussiedler tended to participate in migrant networks after they have moved to Germany. Whereas all studies on the economic effects of migrant networks found a positive impact on the labor market performance of ethnic Germans, the outcome of network participation with respect to social absorption is less encouraging. In recent years migrant networks seem to support ethnic German minority enclaves and an increasing segregation of the Aussiedler group.

High-power tensile-strained GaAsP-AlGaAs quantum-well lasers emitting between 715 and 790 nm

Abstract: Tensile-strained GaAsP quantum wells embedded in AlGaAs large optical cavity structures were studied. In the wavelength range between 715 and 790 nm, very high output power and excellent conversion efficiencies of broad-area lasers have been obtained.

Salt effect on formation and properties of interpolyelectrolyte complexes and their interactions with silica particles

Abstract: The influence of low-molecular-mass salt, namely NaCl, on the properties of interpolyelectrolyte complexes (PECs) formed as a result of interactions between poly(diallyldimethylammonium chloride)(PDADMAC) and copolymers of maleic acid with propene [P(MS-P)] or methylstyrene [P(MS-α-MeSty)] in their salt-containing nonstoichiometric mixtures has been studied by means of turbidimetry, quasi-elastic light scattering, and laser-Doppler microelectrophoresis It has been found that stable dispersions of positively charged PEC particles could be prepared at low salt concentration The hydrodynamic radius of these PEC particles formed at a salt concentration <005 mol/L was shown to be nearly constant and to be in the range of a few hundred nanometers A pronounced salt-induced increase in their size was observed at higher concentrations of NaCl The complex dispersions formed with P(MS-α-MeSty) are more stable to salt than dispersions formed with P(MS-P) The flocculation behavior of silica was investigated by u

Electron beam irradiation of polytetrafluoroethylene in vacuum at elevated temperature: An infrared spectroscopic study

Abstract: Electron beam irradiation of polytetrafluoroethylene (PTFE) has been performed in vacuum both at elevated temperature above the melting point of PTFE and at room temperature for comparison. The changes in the chemical structure were studied by Fourier-transform infrared (FTIR) spectroscopy. The formation of double bonds in PTFE was confirmed as a result of irradiation in vacuum. Moreover, trifluoromethyl (CF3) branches were detected. The concentration of CF3 branches was found to be much higher in irradiation at elevated temperature than in room temperature irradiation. The CF3 branches are assumed to cause the reduced crystallinity indicated by the transparency of PTFE specimens irradiated in the molten state. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1571–1576, 1999

Iron, calcium, and potassium atom densities in the trails of Leonids and other meteors: Strong evidence for differential ablation

Abstract: — We report on studies of the Fe, Ca, and K atom densities in the trails of meteors. The measurements of the densities were taken simultaneously and in a common volume by three ground-based lidars. We report and analyze the data obtained during two nights of Leonid showers (1996 and 1998 November 16/17) and of one night five days after the 1998 Leonids. The lidar-observed trails of Leonids differ from those of other meteor showers in both their mean altitude and in mean metal composition. The Leonid trails show a highly depressed Ca/Fe abundance ratio in comparison to CI meteoritic composition. Our observations are interpreted with the help of a numerical model that describes the ablation processes occurring during the high-speed entry of meteoroids into the Earth's atmosphere. We conclude that for the lidar-observed meteoroids, the ablation process occurs differentially for the three elements. This leads to a mixture of metals in the meteor trails, the composition of which is strongly altitude dependent and at any one altitude deviates significantly from a CI meteoritic composition. The model predicts differing altitudes and durations of trail observations for different showers, allowing us to tentatively assign the origin to the observed trails.

The protective effect of EGb 761 in isolated ischemic/reperfused rat hearts: a link between cardiac function and nitric oxide production.

Abstract: This study was conducted to evaluate the effect of Ginkgo biloba extract (EGb 761) on the nitric oxide (NO) production in relation to the recovery of postischemic cardiac function in isolated working rat hearts. Rats were orally treated with various doses (25, 50, 75, and 100 mg/kg/day) of EGb 761 for 10 days. Hearts were isolated in "working mode" and subjected to 30-min ischemia followed by 120 min of reperfusion. EGb 761 inhibited NO production measured by electron spin-resonance spectroscopy (ESR), and improved the recovery of postischemic cardiac function (coronary flow, aortic flow, left ventricular developed pressure and its first derivative) in the ischemic/reperfused myocardium. Thus in rats treated with 25, 50, 75, and 100 mg/kg/day of EGb 761 and in hearts subjected to 30-min ischemia followed by 120 min of reperfusion, aortic flow was increased from its postischemic drug-free control value of 8.0+/-0.4 to 8.6+/-0.4 ml/min (NS), 17.3+/-0.9 ml/min (p<0.05), 21.5+/-1.1 ml/min (p<0.05), and 23.6+/-1.2 ml/min, respectively. The same recovery in postischemic coronary flow, left ventricular developed pressure, and its first derivative also was observed. In the initial phase of reperfusion, NO production measured by ESR was reduced by 85% in the 75 mg/ kg/day of EGb 761-treated group in comparison with the drug-free ischemic/reperfused hearts. Inducible NO synthase (iNOS) messenger RNA (mRNA) measured by reverse transcription-polymerase chain reaction (RT-PCR) also was reduced by 41 and 58% in the groups treated with 75 and 100 mg/kg/day of EGb 761, respectively. Our findings show that EGb 761 directly acts as an NO scavenger and concomitantly inhibits the expression of iNOS mRNA. Thus, EGb 761 may act as a potent inhibitor of NO production under the condition of ischemia/reperfusion, improving the recovery of postischemic cardiac function.