Showing papers by "Leibniz Association published in 2001"

Indian Ocean Experiment: An integrated analysis of the climate forcing and effects of the great Indo-Asian haze

Abstract: Every year, from December to April, anthropogenic haze spreads over most of the North Indian Ocean, and South and Southeast Asia. The Indian Ocean Experiment (INDOEX) documented this Indo-Asian haze at scales ranging from individual particles to its contribution to the regional climate forcing. This study integrates the multiplatform observations (satellites, aircraft, ships, surface stations, and balloons) with one- and four-dimensional models to derive the regional aerosol forcing resulting from the direct, the semidirect and the two indirect effects. The haze particles consisted of several inorganic and carbonaceous species, including absorbing black carbon clusters, fly ash, and mineral dust. The most striking result was the large loading of aerosols over most of the South Asian region and the North Indian Ocean. The January to March 1999 visible optical depths were about 0.5 over most of the continent and reached values as large as 0.2 over the equatorial Indian ocean due to long-range transport. The aerosol layer extended as high as 3 km. Black carbon contributed about 14% to the fine particle mass and 11% to the visible optical depth. The single-scattering albedo estimated by several independent methods was consistently around 0.9 both inland and over the open ocean. Anthropogenic sources contributed as much as 80% (±10%) to the aerosol loading and the optical depth. The in situ data, which clearly support the existence of the first indirect effect (increased aerosol concentration producing more cloud drops with smaller effective radii), are used to develop a composite indirect effect scheme. The Indo-Asian aerosols impact the radiative forcing through a complex set of heating (positive forcing) and cooling (negative forcing) processes. Clouds and black carbon emerge as the major players. The dominant factor, however, is the large negative forcing (-20±4 W m^(−2)) at the surface and the comparably large atmospheric heating. Regionally, the absorbing haze decreased the surface solar radiation by an amount comparable to 50% of the total ocean heat flux and nearly doubled the lower tropospheric solar heating. We demonstrate with a general circulation model how this additional heating significantly perturbs the tropical rainfall patterns and the hydrological cycle with implications to global climate.

Molecular mechanisms of plant metal tolerance and homeostasis.

Abstract: Transition metals such as copper are essential for many physiological processes yet can be toxic at elevated levels. Other metals (e.g. lead) are nonessential and potentially highly toxic. Plants – like all other organisms – possess homeostatic mechanisms to maintain the correct concentrations of essential metal ions in different cellular compartments and to minimize the damage from exposure to nonessential metal ions. A regulated network of metal transport, chelation, trafficking and sequestration activities functions to provide the uptake, distribution and detoxification of metal ions. Some of the components of this network have now been identified: a number of uptake transporters have been cloned as well as candidate transporters for the vacuolar sequestration of metals. Chelators and chaperones are known, and evidence for intracellular metal trafficking is emerging. This recent progress in the molecular understanding of plant metal homeostasis and tolerance is reviewed.

Glycosyltransferases in secondary plant metabolism: tranquilizers and stimulant controllers

Abstract: Plants are exposed to a wide range of toxic and bioactive low-molecular-weight molecules from both exogenous and endogenous sources. Glycosylation is one of the primary sedative mechanisms that plants utilise in order to maintain metabolic homeostasis. Recently, a range of glycosyltransferases has been characterized in detail with regard to substrate specificity. The next step in increasing our understanding of the biology of glycosylation will require information regarding the exact role of individual glycosyltransferases in planta, as well as an insight into their potential involvement in metabolon-complexes. Hopefully, this will answer how a large number of glycosyltransferases with broad, rather than narrow, substrate specificity can be constrained in order to avoid interfering with other pathways of primary and secondary metabolism. These and other topics are discussed.

Genome duplication events and functional reduction of ploidy levels in sturgeon (Acipenser, Huso and Scaphirhynchus).

Abstract: Sturgeon (order Acipenserformes) provide an ideal taxonomic context for examination of genome duplication events. Multiple levels of ploidy exist among these fish. In a novel microsatellite approach, data from 962 fish from 20 sturgeon species were used for analysis of ploidy in sturgeon. Allele numbers in a sample of individuals were assessed at six microsatellite loci. Species with approximately 120 chromosomes are classified as functional diploid species, species with approximately 250 chromosomes as functional tetraploid species, and with approximately 500 chromosomes as functional octaploids. A molecular phylogeny of the sturgeon was determined on the basis of sequences of the entire mitochondrial cytochrome b gene. By mapping the estimated levels of ploidy on this proposed phylogeny we demonstrate that (I) polyploidization events independently occurred in the acipenseriform radiation; (II) the process of functional genome reduction is nearly finished in species with approximately 120 chromosomes and more active in species with approximately 250 chromosomes and approximately 500 chromosomes; and (III) species with approximately 250 and approximately 500 chromosomes arose more recently than those with approximately 120 chromosomes. These results suggest that gene silencing, chromosomal rearrangements, and transposition events played an important role in the acipenseriform genome formation. Furthermore, this phylogeny is broadly consistent with previous hypotheses but reveals a highly supported oceanic (Atlantic-Pacific) subdivision within the Acipenser/Huso complex.

Immune evasion of Borrelia burgdorferi by acquisition of human complement regulators FHL-1/reconectin and Factor H.

Abstract: To understand immune evasion mechanisms of Borrelia burgdorferi we compared serum-resistant B. afzelii and serum-sensitive B. garinii isolates for their capacity toacquire human complement regulators. Here we demonstrate that the two borrelial genospecies show different binding of the two important human complement regulators, FHL-1/reconectin and Factor H. All serum-resistant B. afzelii isolates bound FHL-1/reconectin and also Factor H, and all analyzed serum-sensitive B. garinii isolates showed no or a significantly lower binding activity. Using recombinant deletion mutants, the binding domains were localized to the C terminus of FHL-1/reconectin to short consensus repeats 5–7. The borrelial binding proteins were located in the surface of the bacteria as demonstrated by immunofluorescence staining of intact, serum-exposed bacteria and by enrichment of outer membrane proteins. The surface-attached complement regulators maintained complement regulatory activity as demonstrated in a cofactor assay. By ligand blotting two different borrelial binding proteins were identified that were responsible for the surface attachment of FHL-1/reconectin and Factor H. These borrelial complement regulators acquiring surface proteins (CRASP) were further characterized as either CRASP-1, a 27.5-kDa molecule which preferentially binds FHL-1/reconectin and which was present in all serum-resistant borreliae, or CRASP-2, a 20/21-kDa protein which interacts preferentially with Factor H and the expression of which was more restricted, being detected in four of the six isolates analyzed. In summary, we describe a new immune evasion mechanism of B. burgdorferi, as these bacteria acquire human complement regulators to control complement activation on their surface and to prevent formation of toxic activation products.

Further Characterization of Complement Regulator-Acquiring Surface Proteins of Borrelia burgdorferi

Abstract: The three genospecies Borrelia burgdorferi, Borrelia garinii, and Borrelia afzelii, all causative agents of Lyme disease, differ in their susceptibilities to human complement-mediated lysis. We recently reported that serum resistance of borrelias correlates largely with their ability to bind the human complement regulators FHL-1/reconectin and factor H. To date, two complement regulator-acquiring-proteins (CRASP-1 and CRASP-2) have been identified in serum-resistant B. afzelii isolates (P. Kraiczy, C. Skerka, M. Kirschfink, V. Brade, and P. F. Zipfel, Eur. J. Immunol. 31:1674–1684, 2001). Here, we present a comprehensive study of the CRASPs detectable in both serum-resistant and intermediate serum-sensitive B. afzelii and B. burgdorferi isolates. These CRASPs were designated according to the genospecies either as BaCRASPs, when derived from B. afzelii, or as BbCRASPs, for proteins identified in B. burgdorferi isolates. Each borrelial isolate expresses distinct CRASPs that can be differentiated by their mobility and binding phenotypes. A detailed comparison reveals overlapping and even identical binding profiles for BaCRASP-1 (27.5 kDa), BbCRASP-1 (25.9 kDa), and BbCRASP-2 (23.2 kDa), which bind FHL-1/reconectin strongly and interact weakly with factor H. In contrast, two B. afzelii proteins (BaCRASP-4 [19.2 kDa] and BaCRASP-5 [22.5 kDa]) and three B. burgdorferi proteins (BbCRASP-3 [19.8 kDa], BbCRASP-4 [18.5 kDa], and BbCRASP-5 [17.7 kDa]) bind factor H but not FHL-1/reconectin. Most CRASPs bind both human immune regulators at their C-terminal ends. Temperature-dependent up-regulation of CRASPs (BaCRASP-1, BaCRASP-2, and BaCRASP-5) is detected in low-passage borrelias cultured at 33 or 37°C compared with those cultured at 20°C. The characterization of the individual CRASPs on the molecular level is expected to identify new virulence factors and potential vaccine candidates.

A harpin binding site in tobacco plasma membranes mediates activation of the pathogenesis-related gene HIN1 independent of extracellular calcium but dependent on mitogen-activated protein kinase activity.

Abstract: Harpin from the bean halo-blight pathogen Pseudomonas syringae pv phaseolicola (harpin(Psph)) elicits the hypersensitive response and the accumulation of pathogenesis-related gene transcripts in the nonhost plant tobacco. Here, we report the characterization of a nonproteinaceous binding site for harpin(Psph) in tobacco plasma membranes, which is assumed to mediate the activation of plant defense responses in a receptor-like manner. Binding of 125I-harpin(Psph) to tobacco microsomal membranes (dissociation constant = 425 nM) and protoplasts (dissociation constant = 380 nM) was specific, reversible, and saturable. A close correlation was found between the abilities of harpin(Psph) fragments to elicit the transcript accumulation of the pathogenesis-related tobacco gene HIN1 and to compete for binding of 125I-harpin(Psph) to its binding site. Another elicitor of the hypersensitive response and HIN1 induction in tobacco, the Phytophthora megasperma-derived beta-elicitin beta-megaspermin, failed to bind to the putative harpin(Psph) receptor. In contrast to activation by beta-megaspermin, harpin(Psph)-induced activation of the 48-kD salicylic acid-responsive mitogen-activated protein kinase (MAPK) and HIN1 transcript accumulation were independent of extracellular calcium. Moreover, use of the MAPK kinase inhibitor U0126 revealed that MAPK activity was essential for pathogenesis-related gene expression in harpin(Psph)-treated tobacco cells. Thus, a receptor-mediated MAPK-dependent signaling pathway may mediate the activation of plant defense responses induced by harpin(Psph).

Field investigation of three-dimensional flow structure at stream confluences: 1. Thermal mixing and time-averaged velocities

Abstract: Stream confluences are characterized by complex patterns of three-dimensional fluid motion. This paper examines the three-dimensional time-averaged flow structure at three concordant-bed confluences in east central Illinois. Two of the junctions have symmetrical planforms, whereas the other has an asymmetrical planform. Similarities among the sites include (1) pronounced convergence of flow at the upstream end of the confluences, (2) a region of stagnated fluid near the upstream junction corner, (3) a well-defined thermal mixing interface between the converging flows that persists downstream of each confluence, (4) a downstream velocity field characterized by two zones of maximum velocity separated by an intervening region of low velocity centered on the mixing interface, (5) convective acceleration of flow within the mixing interface leading to increasing uniformity of the downstream velocity field in the downstream direction, and (6) lateral deflection of flow by the dominant tributary. Prominent helical motion occurs at the asymmetrical confluence, whereas weak helicity is detectable only at one of the two symmetrical confluences. The downstream persistence of a well-defined mixing interface at the two symmetrical confluences and the disruption of this interface at the asymmetrical confluence suggest that helical motion enhances patterns of mixing at confluences.

Experimental set-up for thermopower and resistivity measurements at 100-1300 K

Abstract: In this paper we describe an experimental set-up for simultaneous measurements of thermopower and electrical resistivity at temperatures from 100 K to 1300 K. Optimal configuration of electrodes and original mechanical contacts of thermocouples, current leads and potential probes with the sample make it possible to measure a large variety of materials and result in greater flexibility with respect to the sample form and dimensions. Both bulk and thin film samples with resistances in the range from 0 Ω up to 200 kΩ (1 GΩ in case of the resistivity measurement) can be investigated. Precision and high reliability of the system have been proven during more than three years of use. The resistivity and thermopower of pure Pb, Cu and Ni, and a Cr-Si thin film composite are presented as test materials to demonstrate the possibilities and accuracy of this experimental set-up.

Field investigation of three‐dimensional flow structure at stream confluences: 2. Turbulence

Abstract: Stream confluences are among the most highly turbulent locations in fluvial systems. This paper examines the three-dimensional structure of turbulence at three stream confluences in east central Illinois. The analysis focuses on the characteristics of turbulence both within the shear layer and in the ambient flow. Results show that at the upstream end of each confluence the shear layer occupies a limited portion of the flow cross-sectional area, but turbulence kinetic energy within this layer is 2–3 times greater than the turbulence kinetic energy of the ambient flow, which has turbulence characteristics similar to those for flow in straight channels. Turbulence within the shear layer can be characterized as quasi-two-dimensional in the sense that large-scale turbulence generated by transverse shear is predominantly two dimensional, whereas small-scale turbulence associated with bed friction is three dimensional. Spectral analysis suggests that the structure of fluid motion within the shear layer differs for confluences with symmetrical versus asymmetrical planforms. The shear layer dissipates rapidly as flow enters the downstream channel, even though a well-defined mixing interface persists at downstream locations.

Theory and measurements of flip-chip interconnects for frequencies up to 100 GHz

Abstract: A detailed investigation of flip-chip interconnects up to W-band frequencies is presented in this paper. In a coplanar 50-/spl Omega/ environment, different test structures were fabricated and measured to determine the electromagnetic characteristics of flip-chip multichip modules, such as detuning, reflection at the interconnect, and parasitic coupling. Electromagnetic simulation is used to explain the details behind the measured results. Key to high return loss at the interconnect is a small bump-pad area. Applying simple compensation structures, the frequency range of operation can be further extended. It is shown that a return loss beyond 20 dB in the frequency range up to 80 GHz is achievable along with excellent reproducibility. Measurements on detuning and isolation are also presented.

DNA damage and repair in Arabidopsis thaliana as measured by the comet assay after treatment with different classes of genotoxins.

Abstract: The three protocols of the comet assay A/N, A/A and N/N were for the first time applied to the plant species Arabidopsis thaliana. The purpose of the experiments was to establish conditions for genotoxic exposure causing DNA damage in Arabidopsis nuclei. This is required for comprehensive gene expression profiling with the intention to screen for genes involved in response of Arabidopsis cells to genotoxic stress. Five chemicals belonging to different classes of mutagens (the monofunctional alkylating agents N-methyl-N-nitrosourea and methyl methanesulfonate, the polyfunctional alkylating agent mitomycin C, the radiomimetic bleomycin and the herbicide maleic hydrazide) were tested. Except for maleic hydrazide, dose-dependent increases in DNA damage were found using the A/N comet assay protocol. While a rapid repair of bleomycin-mediated SSBs and DSBs was found, no significant reduction of DNA migration was observed up to 48h after treatment with the monofunctional alkylating agents.

A Novel Protein Elicitor (PaNie) from Pythium aphanidermatum Induces Multiple Defense Responses in Carrot, Arabidopsis, and Tobacco

Abstract: A novel protein elicitor (PaNie(234)) from Pythium aphanidermatum (Edson) Fitzp. was purified, microsequenced, and the corresponding cDNA was cloned. The deduced amino acid sequence contains a putative eukaryotic secretion signal with a proteinase cleavage site. The heterologously expressed elicitor protein without the secretion signal of 21 amino acids (PaNie(213)) triggered programmed cell death and de novo formation of 4-hydroxybenzoic acid in cultured cells of carrot (Daucus carota). Programmed cell death was determined using the tetrazolium assay and DNA laddering. Infiltration of PaNie(213) into the intercellular space of leaves of Arabidopsis (Columbia-0, wild type) resulted in necroses and deposition of callose on the cell walls of spongy parenchyma cells surrounding the necrotic mesophyll cells. Necroses were also formed in tobacco (Nicotiana tabacum cv Wisconsin W38, wild type) and tomato (Lycopersicon esculentum Mill.) but not in maize (Zea mays), oat (Avena sativa), and Tradescantia zebrina (Bosse), indicating that monocotyledonous plants are unable to perceive the signal. The reactions observed after treatment with the purified PaNie(213) were identical to responses measured after treatment with a crude elicitor preparation from the culture medium of P. aphanidermatum, described previously. The availability of the pure protein offers the possibility to isolate the corresponding receptor and its connection to downstream signaling-inducing defense reactions.

Resistance or emigration: response of the high-alpine plant Eritrichium nanum (L.) Gaudin to the ice age within the Central Alps.

Abstract: Two main possibilities regarding glacial survival of the mountain flora of the Alps during the Quaternary have been discussed: the tabula rasa and the nunatak hypotheses Eritrichium nanum (L) Gaudin (Boraginaceae) is a perennial cushion plant, occurring at high elevations of the Central Alps and having a preference for extreme habitats It belongs to a group of high-alpine plants, for which in situ glacial survival on nunataks is ecologically possible By investigating 20 populations of E nanum of potential nunatak and peripheral refugial regions using amplified fragment length polymorphism, considerable genetic differences between populations from the Central Alps and populations from peripheral refugia were detected; hence, the latter probably did not serve as potential sources for the re-colonization of the Central Alps after glaciation Genetic variation was hierarchically structured ( amova), and three genetically distinct regions could be identified in the Central Alps Two of these, the Penninic and Rhaetic Alps, correspond to nunatak regions proposed in the biogeographic literature Populations from the Lepontic Alps formed a third genetic group Genetic correlation (Mantel statistics) was highest within populations, with a modest decline among populations within specific nunatak regions and a negative correlation outside the genetic influence of specific nunatak regions In situ glacial survival in E nanum could be a model for the Quaternary history of other alpine plants, especially those that also occur at high elevations and in similar habitats

Caenorhabditis elegans expresses a functional phytochelatin synthase

Abstract: The formation of phytochelatins, small metal-binding glutathione-derived peptides, is one of the well-studied responses of plants to toxic metal exposure Phytochelatins have also been detected in some fungi and some marine diatoms Genes encoding phytochelatin synthases (PCS) have recently been cloned from Arabidopsis, wheat and Schizosaccharomyces pombe Surprisingly, database searches revealed the presence of a homologous gene in the Caenorhabditis elegans genome, DDBJ/EMBL/GenBank accession no 266513 Here we show that C elegans indeed expresses a gene coding for a functional phytochelatin synthase CePCS complements the Cd2+ sensitivity of a Schizosaccharomyces pombe PCS knock-out strain and confers phytochelatin synthase activity to these cells Thus, phytochelatins may play a role for metal homeostasis also in certain animals

Magnetic, magneto-optical, and structural properties of URhAl from first-principles calculations

Abstract: We present a first-principles investigation of the electronic properties of the intermetallic uranium compound URhAl. Two band-structure methods are employed in our study, the full-potential augmented plane-wave (FLAPW) method, in which the spin-orbit interaction was recently implemented, and the relativistic, non-full-potential, augmented-spherical-wave method. To scrutinize the relativistic implementation of the FLAPW method, we compare the spin and orbital moments on each atom, as well as the magneto-optical Kerr spectra, as calculated with both methods. The computed quantities are remarkably consistent. With the FLAPW method we further investigate the magnetocrystalline anisotropy energy, the x-ray magnetic circular dichroism at the uranium ${M}_{4,5}$ edge, the equilibrium lattice volume, and the bulk modulus. The magnetocrystalline anisotropy energy is computed to be huge, 34 meV per formula unit. The calculated uranium moments exhibit an Ising-like behavior---they almost vanish when the magnetization direction is forced to lie in the uranium planes. The origin of this behavior is analyzed. The calculated optical and magneto-optical spectra, and also the equilibrium lattice parameter and bulk modulus, are found to compare well to the available experimental data, which emphasizes the itinerant character of the $5f$'s in URhAl.

Chromosome painting in plants.

Abstract: The current 'state-of-art' as to chromosome painting in plants is reviewed. We define different situations described as painting so far: i) Genomic in situ hybridisation (GISH) with total genomic DNA to distinguish alien chromosomes on the basis of divergent dispersed repeats, ii) 'Chromosomal in situ suppression' (CISS) hybridisation with chromosome-derived DNA probes and blocking of interchromosomally dispersed repeats by total genomic or C0t-1 DNA in excess, iii) exceptional cases of single chromosome painting by probes containing chromosome-specific dispersed repeats, and iv) Fluorescence in situ hybridisation (FISH) with extended contigs of large insert clones for painting of those chromosomes of a euploid complement which harbour the cloned sequences. While GISH was successfully applied in most plant hybrids and/or their derivatives, painting of individual chromosomes by CISS hybridisations of chromosome-specific DNA probes have so far not revealed convincing results in plants. The reason for this failure and the use of possible alternative approaches are discussed. At least for small plant genomes, painting by large insert single sequence clones provides a promising alternative tool to solve cytogenetic questions, which up to now could not be tackled otherwise. An example of such a painting is described in detail for Arabidopsis thaliana.

Phosphopeptide analysis by positive and negative ion matrix-assisted laser desorption/ionization mass spectrometry.

Abstract: This article describes a simple procedure for the detection of phosphorylated peptides by comparable positive and negative ion mode matrix-assisted laser desorption/ionization mass spectrometry measurements. Based on studies with phosphorylated peptides (EAIXAAPFAK, X = pS, pT, pY) and their corresponding non-phosphorylated analogs, it was found that phosphopeptides, which are characterized by a low ionization efficiency in the positive ion mode, exhibit drastically increased signal intensities in the negative ion mode compared to their non-phosphorylated analogs. The effect was successfully used to identify phosphorylated sequences of the commonly used phosphoprotein standards, protein kinase A and beta-casein, by peptide mass fingerprint analyses of the corresponding Lys C and trypsin digests using both (positive and negative) ion modes. The comparison of positive and negative ion spectra of a given protein digest (relative intensity([M - H]-)/relative intensity([M + H]+)) can be used to identify any phosphopeptides present which may then be separated and analyzed further.

Evaluating Environmental Programs: The Perspective of Modern Evaluation Research

Abstract: Large-scale environmental programs generally commit substantial societal resources, making the evaluation of their actual effects on the relevant outcomes imperative. As the example of the subsidization of energy-saving appliances illustrates, much of the applied environmental economics literature has yet to confront the problem of proper attribution of effects to underlying causes on a convincing methodological basis. This paper argues that recent results in the econometrics and statistics literature on program evaluation could be utilized to advance considerably in this context. In particular, the construction of a credible counterfactual situation is at the heart of the formal statistical evaluation problem. Even when controlled experiments are not a viable option, appropriate approaches might succeed where traditional empirical strategies fail to uncover the effects of environmental interventions.

Reconciling fossils and molecules: Cenozoic divergence of cichlid fishes and the biogeography of Madagascar

Abstract: Aim The biogeographical origins of the extant vertebrates endemic to Madagascar are largely unsolved, but have often been related to vicariance in the context of fragmentation of the supercontinent Gondwana in the Mesozoic. Such hypotheses are especially appealing in the case of cichlid fishes, which show phylogenetic relationships reflecting the temporal successions of the breakup of Gondwana. We used molecular clock data to test this assumption. Location Fragments of the 16S rRNA gene and of the nuclear Tmo-4C4 locus, partly obtained from Genbank from South American, African, Malagasy and Indian cichlids were analysed. Methods Based on monophyletic cichlid radiations in African lakes, we calibrated a molecular clock. The obtained rates were used to estimate the age of divergence of the major cichlid clades. Results The results agreed better with a Cenozoic than with a Mesozoic divergence, and were in accordance with the fossil record. Sequence divergences of the 16S and 12S rRNA genes of most lineages of Malagasy terrestrial and freshwater vertebrates from their non-Malagasy sister groups were below saturation and many were relatively similar to those of cichlids. Main conclusions A Cenozoic dispersal from continental landmasses may explain the origin of most extant Malagasy vertebrate groups better than a Jurassic/Cretaceous vicariance.