13 research outputs found

    Charakterisierung Ionenkanal-bildender Substanzen aus dem Regurgitat von Lepidoptera-Larven

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    Die vorliegende Arbeit befasst sich mit den sehr frühen Ereignissen während des Befalls von Pflanzen durch Raupen. Als erste Reaktion der Pflanze wird eine Depolarisation der Plasmamembran gemessen. Als Auslöser hierfür gelten beispielsweise Fettsäure- Aminosäurekonjugate oder Wasserstoffperoxid im Regurgitat von Raupen. In dieser Arbeit wurde eine weitere mögliche Ursache für die Depolarisation beschrieben und untersucht. Im Regurgitat von Raupen finden sich Ionenkanal-bildende Substanzen. Diese wurden durch die BLM-Technik nachgewiesen. Mit Hilfe dieser Technik wurde gezeigt, dass die genannten Ionenkanal-bildenden Substanzen spontan in künstliche, planare Lipiddoppelschichten aus pflanzlichen Lipiden ohne Membranproteine inserieren und dadurch die Leitfähigkeit der Membran erheblich erhöhen. Derartige Ionenkanal-bildenden Verbindungen ließen sich im Regurgitat der Larven von acht verschiedenen Arten aus vier Familien nachweisen. Die phylogenetisch weite Verbreitung dieser Ionenkanal-bildenden Substanzen weist auf generelle Bedeutung für die Larven von Lepidopteren hin. Die Ionenkanäle, die durch das Regurgitat von S. exigua in planaren Lipiddoppelschichten erzeugt wurden, besitzen eine Kationenselektivität bei Kaliumchlorid von etwa 5:1. Es ist gelungen, die Ionenkanal-bildenden Substanzen aus dem Regurgitat von S. littoralis weitgehend aufzureinigen. Die Modellsubstanz Alamethicin war in der Lage, das Membranpotenzial in Blättern von Phaseolus lunatus lokal und von Hordeum vulgare auch systemisch zu depolarisieren. Durch diesen Nachweis wurde die experimentelle Lücke geschlossen und gezeigt, dass Ionenkanal-bildende Substanzen auch bei Pflanzen zur Depolarisation der Plasmamembran führen können. Diese Depolarisation wiederum, wie sie auch bei dem Fressen von Raupen an Pflanzen gemessen wird, kann sowohl Signalcharakter für die Pflanze besitzen als auch ein Versuch des Insekts sein, die Reaktionsfähigkeit der pflanzlichen Zelle zu beeinflussen

    Adaptive time-domain boundary element methods and engineering applications

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    Adaptive FE-BE Coupling for Strongly Nonlinear Transmission Problems with Coulomb Friction

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    We analyze an adaptive finite element/boundary element procedure for scalar elastoplastic interface problems involving friction, where a nonlinear uniformly monotone operator such as the p-Laplacian is coupled to the linear Laplace equation on the exterior domain. The problem is reduced to a boundary/domain variational inequality, a discretized saddle point formulation of which is then solved using the Uzawa algorithm and adaptive mesh refinements based on a gradient recovery scheme. The Galerkin approximations are shown to converge to the unique solution of the variational problem in a suitable product of L^p- and L^2-Sobolev spaces.Comment: 27 pages, 3 figure

    Functional characterization of a class III acid endochitinase from the traps of the carnivorous pitcher plant genus, Nepenthes

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    Carnivory in plants is an adaptation strategy to nutrient-poor environments and soils. Carnivorous plants obtain some additional mineral nutrients by trapping and digesting prey; the genus Nepenthes is helped by its specialized pitcher traps. To make the nutrients available, the caught prey needs to be digested, a process that requires the concerted activity of several hydrolytic enzymes. To identify and investigate the various enzymes involved in this process, fluid from Nepenthes traps has been analysed in detail. In this study, a novel type of Nepenthes endochitinase was identified in the digestion fluid of closed pitchers. The encoding endochitinase genes have been cloned from eight different Nepenthes species. Among these, the deduced amino acid sequence similarity was at least 94.9%. The corresponding cDNA from N. rafflesiana was heterologously expressed, and the purified protein, NrChit1, was biochemically characterized. The enzyme, classified as a class III acid endochitinase belonging to family 18 of the glycoside hydrolases, is secreted into the pitcher fluid very probably due to the presence of an N-terminal signal peptide. Transcriptome analyses using real-time PCR indicated that the presence of prey in the pitcher up-regulates the endochitinase gene not only in the glands, which are responsible for enzyme secretion, but at an even higher level, in the glands’ surrounding tissue. These results suggest that in the pitchers’ tissues, the endochitinase as well as other proteins from the pitcher fluid might fulfil a different, primary function as pathogenesis-related proteins

    FE–BE coupling for a transmission problem involving microstructure, in preparation

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    Abstract We analyze a finite element/boundary element procedure for a non-convex contact problem for the double-well potential. After relaxing the associated functional, the degenerate minimization problem is reduced to a boundary/domain variational inequality, a discretized saddle point formulation of which may then be solved numerically. The convergence of the Galerkin approximations to certain macroscopic quantities and a corresponding a posteriori estimate for the approximation error are discussed. Numerical results illustrate the performance of the proposed method

    Solving approximate cloaking problems using finite element methods

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    Motivated by the approximate cloaking problem, we consider a variable coefficient Helmholtz equation with a fixed wave number. We use finite element methods to discretize the equation. Numerical results are shown to exhibit cloaking behaviour. References A. Alu and N. Engheta. Achieving transparency with plasmonic and metamaterial coatings. Phys. Rev. E 72:016623, 2005. doi:10.1103/PhysRevE.72.016623 W. Cai, U. K. Chettiar, A. V. Kildishev and V. M. Shalaev. Optical cloaking with metamaterials. Nature Photonics 1:224–227, 2007. doi:10.1038/nphoton.2007.28 A. Greenleaf, Y. Kurylev, M. Lassas and G. Uhlmann. Cloaking devices, electromagnetic wormholes and transformation optics. SIAM Rev. 51:3–33, 2009. doi:10.1137/080716827 R. V. Kohn, D. Onofrei, M. S. Vogelius and M. I. Weinstein. Cloaking via change of variables for the Helmholtz equation. Comm. Pure Appl. Math. 63:973–1016, 2010. doi:10.1002/cpa.20341 R. V. Kohn, H. Shen, M. S. Vogelius and M. I. Weinstein. Cloaking via change of variables in electric impedance tomography. Inverse Problems 24:015016, 2008. doi:10.1088/0266-5611/24/1/015016 U. Leonhardt. Optical conformal mapping. Science 312:1777–1780, 2006. doi:10.1126/science.1126493 M. Maischak. Book of Numerical Experiments (B.O.N.E). http://www.ifam.uni-hannover.de/ maiprogs/ J. B. Pendry, D. Schurig and D. R. Smith. Controlling electromagnetic fields. Science 312:1780–1782, 2006. doi:10.1126/science.1125907 D. Schurig, J. Mock, B. Justice, S. Cummer, J. Pendry, A. Starr and D. Smith. Metamaterial electromagnetic cloak at microwave frequencies. Science 314:977–980, 2006. doi:10.1126/science.113362

    Multi-laboratory validation of a new marine biodegradation screening test for chemical persistence assessment

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    Embargo until 12 March 2021Current biodegradation screening tests are not specifically designed for persistence assessment of chemicals, often show high inter- and intra-test variability, and often give false negative biodegradation results. Based on previous studies and recommendations, an international ring test involving 13 laboratories validated a new test method for marine biodegradation with a focus on improving the reliability of screening to determine the environmental degradation potential of chemicals. The new method incorporated increased bacterial cell concentrations to better represent the microbial diversity; a chemical is likely to be exposed in the sampled environments and ran beyond 60 days, which is the half-life threshold for chemical persistence in the marine environment. The new test provided a more reliable and less variable characterization of the biodegradation behavior of five reference chemicals (sodium benzoate, triethanolamine, 4-nitrophenol, anionic polyacrylamide, and pentachlorophenol), with respect to REACH and OSPAR persistence thresholds, than the current OECD 306 test. The proposed new method provides a cost-effective screening test for non-persistence that could streamline chemical regulation and reduce the cost and animal welfare implications of further higher tier testing.acceptedVersio