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Showing papers by "Hungarian Academy of Sciences published in 2006"


Journal ArticleDOI
TL;DR: Various approaches to combating multidrug-resistant cancer are described, including the development of drugs that engage, evade or exploit efflux by ABC transporters.
Abstract: Effective treatment of metastatic cancers usually requires the use of toxic chemotherapy. In most cases, multiple drugs are used, as resistance to single agents occurs almost universally. For this reason, elucidation of mechanisms that confer simultaneous resistance to different drugs with different targets and chemical structures - multidrug resistance - has been a major goal of cancer biologists during the past 35 years. Here, we review the most common of these mechanisms, one that relies on drug efflux from cancer cells mediated by ATP-binding cassette (ABC) transporters. We describe various approaches to combating multidrug-resistant cancer, including the development of drugs that engage, evade or exploit efflux by ABC transporters.

3,147 citations


Book ChapterDOI
18 Sep 2006
TL;DR: In this article, a bandit-based Monte-Carlo planning algorithm is proposed for large state-space Markovian decision problems (MDPs), which is one of the few viable approaches to find near-optimal solutions.
Abstract: For large state-space Markovian Decision Problems Monte-Carlo planning is one of the few viable approaches to find near-optimal solutions. In this paper we introduce a new algorithm, UCT, that applies bandit ideas to guide Monte-Carlo planning. In finite-horizon or discounted MDPs the algorithm is shown to be consistent and finite sample bounds are derived on the estimation error due to sampling. Experimental results show that in several domains, UCT is significantly more efficient than its alternatives.

2,695 citations


Journal ArticleDOI
TL;DR: In this article, the authors show that brown carbon may severely bias measurements of atmospheric "black carbon" and "elemental carbon" over vast parts of the troposphere, especially those strongly polluted by biomass burning, where the mass concentration of C brown is high relative to that of soot carbon.
Abstract: Although the definition and measurement techniques for atmospheric "black carbon" ("BC") or "elemental carbon'' ("EC") have long been subjects of scientific controversy, the recent discovery of light-absorbing carbon that is not black ("brown carbon, C brown ") makes it imperative to reassess and redefine the components that make up light-absorbing carbonaceous matter (LAC) in the atmosphere. Evidence for the atmospheric presence of C brown comes from (1) spectral aerosol light absorption measurements near specific combustion sources, (2) observations of spectral properties of water extracts of continental aerosol, (3) laboratory studies indicating the formation of light-absorbing organic matter in the atmosphere, and (4) indirectly from the chemical analogy of aerosol species to colored natural humic substances. We show that brown carbon may severely bias measurements of "BC" and "EC" over vast parts of the troposphere, especially those strongly polluted by biomass burning, where the mass concentration of C brown is high relative to that of soot carbon. Chemical measurements to determine "EC" are biased by the refractory nature of C brown as well as by complex matrix interferences. Optical measurements of "BC" suffer from a number of problems: (1) many of the presently used instruments introduce a substantial bias into the determination of aerosol light absorption, (2) there is no unique conversion factor between light absorption and "EC" or "BC" concentration in ambient aerosols, and (3) the difference in spectral properties between the different types of LAC, as well as the chemical complexity of C brown , lead to several conceptual as well as practical complications. We also suggest that due to the sharply increasing absorption of C brown towards the UV, single-wavelength light absorption measurements may not be adequate for the assessment of absorption of solar radiation in the troposphere. We discuss the possible consequences of these effects for our understanding of tropospheric processes, including their influence on UV-irradiance, atmospheric photochemistry and radiative transfer in clouds.

1,706 citations


Journal ArticleDOI
TL;DR: In this paper, the authors employed a matrix-based power spectrum estimation method using pseudo-Karhunen-Loeve eigenmodes, producing uncorrelated minimum-variance measurements in 20 k-bands of both the clustering power and its anisotropy due to redshift-space distortions.
Abstract: We measure the large-scale real-space power spectrum P(k) using luminous red galaxies (LRGs) in the Sloan Digital Sky Survey (SDSS) and use this measurement to sharpen constraints on cosmological parameters from the Wilkinson Microwave Anisotropy Probe (WMAP). We employ a matrix-based power spectrum estimation method using Pseudo-Karhunen-Loeve eigenmodes, producing uncorrelated minimum-variance measurements in 20 k-bands of both the clustering power and its anisotropy due to redshift-space distortions, with narrow and well-behaved window functions in the range 0.01h/Mpc 0.1h/Mpc and associated nonlinear complications, yet agree well with more aggressive published analyses where nonlinear modeling is crucial.

1,481 citations


Journal ArticleDOI
17 Mar 2006-Science
TL;DR: In DESI as discussed by the authors, electrically charged droplets are directed at the ambient object of interest; they release ions from the surface, which are then vacuumed through the air into a conventional mass spectrometer.
Abstract: A recent innovation in mass spectrometry is the ability to record mass spectra on ordinary samples, in their native environment, without sample preparation or preseparation by creating ions outside the instrument. In desorption electrospray ionization (DESI), the principal method described here, electrically charged droplets are directed at the ambient object of interest; they release ions from the surface, which are then vacuumed through the air into a conventional mass spectrometer. Extremely rapid analysis is coupled with high sensitivity and high chemical specificity. These characteristics are advantageously applied to high-throughput metabolomics, explosives detection, natural products discovery, and biological tissue imaging, among other applications. Future possible uses of DESI for in vivo clinical analysis and its adaptation to portable mass spectrometers are described.

1,307 citations


Journal ArticleDOI
TL;DR: It is shown that in gene (protein) association networks CFinder can be used to predict the function(s) of a single protein and to discover novel modules, and CFinder is also very efficient for locating the cliques of large sparse graphs.
Abstract: Summary: Most cellular tasks are performed not by individual proteins, but by groups of functionally associated proteins, often referred to as modules. In a protein assocation network modules appear as groups of densely interconnected nodes, also called communities or clusters. These modules often overlap with each other and form a network of their own, in which nodes (links) represent the modules (overlaps). We introduce CFinder, a fast program locating and visualizing overlapping, densely interconnected groups of nodes in undirected graphs, and allowing the user to easily navigate between the original graph and the web of these groups. We show that in gene (protein) association networks CFinder can be used to predict the function(s) of a single protein and to discover novel modules. CFinder is also very efficient for locating the cliques of large sparse graphs. Availability: CFinder (for Windows, Linux and Macintosh) and its manual can be downloaded from http://angel.elte.hu/clustering. Supplementary information: Supplementary data are available on Bioinformatics online. Contact: cfinder@angel.elte.hu

879 citations


Journal ArticleDOI
TL;DR: It is suggested that multidrug transporters are essential parts of an innate defense system, the "chemoimmunity" network, which has a number of features reminiscent of classical immunology.
Abstract: In this review we give an overview of the physiological functions of a group of ATP binding cassette (ABC) transporter proteins, which were discovered, and still referred to, as multidrug resistanc...

689 citations


Journal ArticleDOI
TL;DR: It is demonstrated that the expression of mSOD1G93A results in activated and neurotoxic microglia, and suggested that the lack of m SOD1 G93A expression inmicroglia may contribute to motoneuron protection, and confirmed the importance of microglio as a double-edged sword.
Abstract: The most common inherited form of amyotrophic lateral sclerosis (ALS), a neurodegenerative disease affecting adult motoneurons, is caused by dominant mutations in the ubiquitously expressed Cu2+/Zn2+ superoxide dismutase (SOD1). Recent studies suggest that glia may contribute to motoneuron injury in animal models of familial ALS. To determine whether the expression of mutant SOD1 (mSOD1G93A) in CNS microglia contributes to motoneuron injury, PU.1−/− mice that are unable to develop myeloid and lymphoid cells received bone marrow transplants resulting in donor-derived microglia. Donor-derived microglia from mice overexpressing mSOD1G93A, an animal model of familial ALS, transplanted into PU.1−/− mice could not induce weakness, motoneuron injury, or an ALS-like disease. To determine whether expression of mSOD1G93A in motoneurons and astroglia, as well as microglia, was required to produce motoneuron disease, PU.1−/− mice were bred with mSOD1G93A mice. In mSOD1G93A/PU.1−/− mice, wild-type donor-derived microglia slowed motoneuron loss and prolonged disease duration and survival when compared with mice receiving mSOD1G93A expressing cells or mSOD1G93A mice. In vitro studies confirmed that wild-type microglia were less neurotoxic than similarly cultured mSOD1G93A microglia. Compared with wild-type microglia, mSOD1G93A microglia produced and released more superoxide and nitrite+nitrate, and induced more neuronal death. These data demonstrate that the expression of mSOD1G93A results in activated and neurotoxic microglia, and suggests that the lack of mSOD1G93A expression in microglia may contribute to motoneuron protection. This study confirms the importance of microglia as a double-edged sword, and focuses on the importance of targeting microglia to minimize cytotoxicity and maximize neuroprotection in neurodegenerative diseases.

687 citations


Journal ArticleDOI
TL;DR: The evolution of agent technologies and manufacturing will probably proceed hand in hand and the former can receive real challenges from the latter, which will have more and more benefits in applying agent technologies, presumably together with well-established or emerging approaches of other disciplines.
Abstract: The emerging paradigm of agent-based computation has revolutionized the building of intelligent and decentralized systems. The new technologies met well the requirements in all domains of manufacturing where problems of uncertainty and temporal dynamics, information sharing and distributed operation, or coordination and cooperation of autonomous entities had to be tackled. In the paper software agents and multi-agent systems are introduced and through a comprehensive survey, their potential manufacturing applications are outlined. Special emphasis is laid on methodological issues and deployed industrial systems. After discussing open issues and strategic research directions, we conclude that the evolution of agent technologies and manufacturing will probably proceed hand in hand. The former can receive real challenges from the latter, which, in turn, will have more and more benefits in applying agent technologies, presumably together with well-established or emerging approaches of other disciplines.

668 citations


Journal ArticleDOI
TL;DR: It is suggested that a h-type index - equal to h if you have published h papers, each of which has at least h citations - would be a useful supplement to journal impact factors.
Abstract: We suggest that a h-type index - equal to h if you have published h papers, each of which has at least h citations - would be a useful supplement to journal impact factors.

661 citations


Journal ArticleDOI
Pietro Cortese, G. Dellacasa, Luciano Ramello, M. Sitta  +975 moreInstitutions (78)
TL;DR: The ALICE Collaboration as mentioned in this paper is a general-purpose heavy-ion experiment designed to study the physics of strongly interacting matter and the quark-gluon plasma in nucleus-nucleus collisions at the LHC.
Abstract: ALICE is a general-purpose heavy-ion experiment designed to study the physics of strongly interacting matter and the quark–gluon plasma in nucleus–nucleus collisions at the LHC. It currently involves more than 900 physicists and senior engineers, from both the nuclear and high-energy physics sectors, from over 90 institutions in about 30 countries.The ALICE detector is designed to cope with the highest particle multiplicities above those anticipated for Pb–Pb collisions (dNch/dy up to 8000) and it will be operational at the start-up of the LHC. In addition to heavy systems, the ALICE Collaboration will study collisions of lower-mass ions, which are a means of varying the energy density, and protons (both pp and pA), which primarily provide reference data for the nucleus–nucleus collisions. In addition, the pp data will allow for a number of genuine pp physics studies.The detailed design of the different detector systems has been laid down in a number of Technical Design Reports issued between mid-1998 and the end of 2004. The experiment is currently under construction and will be ready for data taking with both proton and heavy-ion beams at the start-up of the LHC.Since the comprehensive information on detector and physics performance was last published in the ALICE Technical Proposal in 1996, the detector, as well as simulation, reconstruction and analysis software have undergone significant development. The Physics Performance Report (PPR) provides an updated and comprehensive summary of the performance of the various ALICE subsystems, including updates to the Technical Design Reports, as appropriate.The PPR is divided into two volumes. Volume I, published in 2004 (CERN/LHCC 2003-049, ALICE Collaboration 2004 J. Phys. G: Nucl. Part. Phys. 30 1517–1763), contains in four chapters a short theoretical overview and an extensive reference list concerning the physics topics of interest to ALICE, the experimental conditions at the LHC, a short summary and update of the subsystem designs, and a description of the offline framework and Monte Carlo event generators.The present volume, Volume II, contains the majority of the information relevant to the physics performance in proton–proton, proton–nucleus, and nucleus–nucleus collisions. Following an introductory overview, Chapter 5 describes the combined detector performance and the event reconstruction procedures, based on detailed simulations of the individual subsystems. Chapter 6 describes the analysis and physics reach for a representative sample of physics observables, from global event characteristics to hard processes.

Journal ArticleDOI
TL;DR: Bioenergetic factors that promote ROS generation at physiologically relevant sites in mitochondria are focused on and emphasis is given to ROS generation by complex I--the first component of the respiratory chain--and to how the NADH:NAD+ ratio regulates ROS formation.

Journal ArticleDOI
TL;DR: It is shown, by using two independent riboprobes, that principal cell populations of the hippocampus express high levels of diacylglycerol lipase α (DGL-α), the enzyme involved in generation of the endocannabinoid 2-arachidonoyl- glycerol (2-AG), which may contribute to homosynaptic plasticity of excitatory synapses and to heterosynptic plasticity between excitatories and inhibitory contacts.
Abstract: Endocannabinoids play central roles in retrograde signaling at a wide variety of synapses throughout the CNS. Although several molecular components of the endocannabinoid system have been identified recently, their precise location and contribution to retrograde synaptic signaling is essentially unknown. Here we show, by using two independent riboprobes, that principal cell populations of the hippocampus express high levels of diacylglycerol lipase alpha (DGL-alpha), the enzyme involved in generation of the endocannabinoid 2-arachidonoyl-glycerol (2-AG). Immunostaining with two independent antibodies against DGL-alpha revealed that this lipase was concentrated in heads of dendritic spines throughout the hippocampal formation. Furthermore, quantification of high-resolution immunoelectron microscopic data showed that this enzyme was highly compartmentalized into a wide perisynaptic annulus around the postsynaptic density of axospinous contacts but did not occur intrasynaptically. On the opposite side of the synapse, the axon terminals forming these excitatory contacts were found to be equipped with presynaptic CB1 cannabinoid receptors. This precise anatomical positioning suggests that 2-AG produced by DGL-alpha on spine heads may be involved in retrograde synaptic signaling at glutamatergic synapses, whereas CB1 receptors located on the afferent terminals are in an ideal position to bind 2-AG and thereby adjust presynaptic glutamate release as a function of postsynaptic activity. We propose that this molecular composition of the endocannabinoid system may be a general feature of most glutamatergic synapses throughout the brain and may contribute to homosynaptic plasticity of excitatory synapses and to heterosynaptic plasticity between excitatory and inhibitory contacts.

Journal ArticleDOI
01 Mar 2006-Carbon
TL;DR: In this article, a pH-potentiometric study explores the factors influencing the surface charge developed in aqueous dispersions of graphite oxide (GO) after a series of oxidation treatments.

Journal ArticleDOI
TL;DR: In this article, the concentrations of 16 US-EPA criteria polycyclic aromatic hydrocarbons (PAHs) were monitored during various seasons at six different cities/locations in the northern part of Belgium.

Journal ArticleDOI
TL;DR: It is demonstrated that differentiation of bacteroids in indeterminate nodules of Medicago and related legumes from the galegoid clade shows remarkable similarity to host cell differentiation, which reveals a positive correlation in prokaryotes between DNA content and cell size, similar to that in eukaryotes.
Abstract: Symbiosis between legumes and Rhizobium bacteria leads to the formation of root nodules where bacteria in the infected plant cells are converted into nitrogen-fixing bacteroids. Nodules with a persistent meristem are indeterminate, whereas nodules without meristem are determinate. The symbiotic plant cells in both nodule types are polyploid because of several cycles of endoreduplication (genome replication without mitosis and cytokinesis) and grow consequently to extreme sizes. Here we demonstrate that differentiation of bacteroids in indeterminate nodules of Medicago and related legumes from the galegoid clade shows remarkable similarity to host cell differentiation. During bacteroid maturation, repeated DNA replication without cytokinesis results in extensive amplification of the entire bacterial genome and elongation of bacteria. This finding reveals a positive correlation in prokaryotes between DNA content and cell size, similar to that in eukaryotes. These polyploid bacteroids are metabolically functional but display increased membrane permeability and are nonviable, because they lose their ability to resume growth. In contrast, bacteroids in determinate nodules of the nongalegoid legumes lotus and bean are comparable to free-living bacteria in their genomic DNA content, cell size, and viability. Using recombinant Rhizobium strains nodulating both legume types, we show that bacteroid differentiation is controlled by the host plant. Plant factors present in nodules of galegoid legumes but absent from nodules of nongalegoid legumes block bacterial cell division and trigger endoreduplication cycles, thereby forcing the endosymbionts toward a terminally differentiated state. Hence, Medicago and related legumes have evolved a mechanism to dominate the symbiosis.

Journal ArticleDOI
TL;DR: In this paper, the degree of hydration and the kinetics of water uptake depend crucially on the preparation and aging conditions of graphite oxide (GO) compounds, and the best sample they have ever got shows layer distances of 8, 9 and 11.5 A u at relative humidities of 45, 75 and 100%, respectively.

Journal ArticleDOI
TL;DR: The goal of the study was to establish if there was a relationship between molecular patterns and virus evolution, and the complete genome sequence of two distinct apathogenic Newcastle disease virus (NDV) strains was determined and a third genome size category, containing 15,198 nucleotides, was recognized.

Journal ArticleDOI
TL;DR: Since they may play a prominent role in certain neurologic disorders, such as ischemia-reperfusion injury, Alzheimer's disease, spinal cord injury and sensory neuropathies, the pathological role and potential therapeutic exploitation of P2X(7) receptors are discussed.

Journal ArticleDOI
TL;DR: iCSD estimates of stimulus-evoked responses measured with laminar electrodes in the rat somatosensory (barrel) cortex are compared to estimates from the standard CSD method.

Journal ArticleDOI
TL;DR: This view contradicts the prevailing view that scaling in protein interactomes arose from gene duplication and preferential attachment of equivalent proteins and proposes an alternative evolutionary network specialization process, in which certain components of the protein interactome improved their fitness for binding by becoming longer or accruing regions of disorder and/or internal repeats and have become specialized in network organization.
Abstract: Protein interaction networks display approximate scale-free topology, in which hub proteins that interact with a large number of other proteins determine the overall organization of the network. In this study, we aim to determine whether hubs are distinguishable from other networked proteins by specific sequence features. Proteins of different connectednesses were compared in the interaction networks of Saccharomyces cerevisiae, Drosophila melanogaster, Caenorhabditis elegans, and Homo sapiens with respect to the distribution of predicted structural disorder, sequence repeats, low complexity regions, and chain length. Highly connected proteins (“hub proteins”) contained significantly more of, and greater proportion of, these sequence features and tended to be longer overall as compared to less connected proteins. These sequence features provide two different functional means for realizing multiple interactions: (1) extended interaction surface and (2) flexibility and adaptability, providing a mechanism for the same region to bind distinct partners. Our view contradicts the prevailing view that scaling in protein interactomes arose from gene duplication and preferential attachment of equivalent proteins. We propose an alternative evolutionary network specialization process, in which certain components of the protein interactome improved their fitness for binding by becoming longer or accruing regions of disorder and/or internal repeats and have therefore become specialized in network organization.

Journal ArticleDOI
TL;DR: In this article, the authors reviewed tectonic processes, structural styles, stratigraphic records and geochemical data for volcanic rocks, and concluded that continental collision and back-arc basin evolution is a single, complex dynamic process with minimization of the potential and deformational energy as the driving principle.
Abstract: The past decade has witnessed spectacular progress in the collection of observational data and their interpretation in the Pannonian Basin and the surrounding Alpine, Carpathian and Dinaric mountain belts. A major driving force behind this progress was the PANCARDI project of the EUROPROBE programme. The paper reviews tectonic processes, structural styles, stratigraphic records and geochemical data for volcanic rocks. Structural and seismic sections of different scales, seismic tomography and magnetotelluric, gravity and geothermal data are also used to determine the deformational styles, and to compile new crustal and lithospheric thickness maps of the Pannonian Basin and the surrounding fold-and-thrust belts. The Pannonian Basin is superimposed on former Alpine terranes. Its formation is a result of extensional collapse of the overthickened Alpine orogenic wedge during orogen-parallel extrusion towards a 9free boundary9 offered by the roll-back of the subducting Carpathian slab. As a conclusion, continental collision and back-arc basin evolution is discussed as a single, complex dynamic process, with minimization of the potential and deformational energy as the driving principle.

Journal ArticleDOI
TL;DR: Evidence is provided that sebocytes are capable of producing proinflammatory cytokines/chemokines and antimicrobial peptides, which may have a role in acne pathogenesis, and that different strains of P. acnes vary in their capacity to stimulate an inflammatory response within the pilosebaceous follicle.

Journal ArticleDOI
TL;DR: In this paper, the authors present an overview of the various methods available for calculating equilibrium exchange rates and discuss how useful they are likely to be for the transition economies of the former soviet bloc.
Abstract: In this paper, we present an overview of a number of issues relating to the equilibrium exchange rates of transition economies of the former soviet bloc. In particular, we present a critical overview of the various methods available for calculating equilibrium exchange rates and discuss how useful they are likely to be for the transition economies. Amongst our findings is the result that the trend appreciation usually observed for the exchange rates of these economies is affected by factors other than the usual Balassa-Samuelson effect, such as the behaviour of the real exchange rate of the open sector and regulated prices. We then consider three main sources of uncertainty relating to the implementation of an equilibrium exchange rate model, namely: differences in the theoretical underpinnings, differences in the econometric estimation techniques, and differences relating to the time-series and cross-sectional dimensions of the data. The ensuing three-dimensional space of real misalignments is probably a useful tool in determining the direction of a possible misalignment rather than its precise size. Copyright Blackwell Publishers Ltd, 2006.

Journal ArticleDOI
TL;DR: DHA diet decreased the number of activated microglia in hippocampus and increased exploratory activity of transgenic mice, but did not improve their spatial learning in the water maze.

Journal ArticleDOI
TL;DR: A real‐world application scenario that uses three distinct types of workflow within the Triana problem‐solving environment: serial scientific workflow for the data processing of gravitational wave signals; job submission workflows that execute Triana services on a testbed; and monitoring workflow that examine and modify the behaviour of the executing application.
Abstract: In this paper, we discuss a real-world application scenario that uses three distinct types of workflow within the Triana problem-solving environment: serial scientific workflow for the data processing of gravitational wave signals; job submission workflows that execute Triana services on a testbed; and monitoring workflows that examine and modify the behaviour of the executing application. We briefly describe the Triana distribution mechanisms and the underlying architectures that we can support. Our middleware independent abstraction layer, called the Grid Application Prototype (GAP), enables us to advertise, discover and communicate with Web and peer-to-peer (P2P) services. We show how gravitational wave search algorithms have been implemented to distribute both the search computation and data across the European GridLab testbed, using a combination of Web services, Globus interaction and P2P infrastructures.

Journal ArticleDOI
TL;DR: In this article, a list of 60 debris disks that exhibit the highest fractional luminosity values in the vicinity of the Sun (i.e., fd > 10 � 4 ) in the IRAS and ISO databases was compiled.
Abstract: By searching the IRAS and ISO databases, we compiled a list of 60 debris disks that exhibit the highest fractional luminosity values ( fd > 10 � 4 ) in the vicinity of the Sun (d 5 ; 10 � 4 are younger than 100 Myr.Thedistribution of the disks inthe fractional luminosityversus age diagram indicates that (1) the number of old systems with high fd is lower than was claimed before, (2) there exist many relatively young disks of moderate fractional luminosity, and (3) comparing the observations with a current theoretical model of debris disk evolution, a general good agreement could be found. Subject headings: circumstellar matter — infrared: stars — stars: kinematics

Journal ArticleDOI
TL;DR: The dynamics of visitation of a major news portal, representing the prototype for such a rapidly evolving network, is investigated, finding that the visitation pattern of a news document decays as a power law, in contrast with the exponential prediction provided by simple models of site visitation.
Abstract: different, the skeleton acquiring visits at a constant rate, while a news document’s visitation peaks after a few hours. We find that the visitation pattern of a news document decays as a power law, in contrast with the exponential prediction provided by simple models of site visitation. This is rooted in the inhomogeneous nature of the browsing pattern characterizing individual users: the time interval between consecutive visits by the same user to the site follows a power-law distribution, in contrast to the exponential expected for Poisson processes. We show that the exponent characterizing the individual user’s browsing patterns determines the power-law decay in a document’s visitation. Finally, our results document the fleeting quality of news and events: while fifteen minutes of fame is still an exaggeration in the online media, we find that access to most news items significantly decays after 36 hours of posting.

Journal ArticleDOI
TL;DR: In this paper, the structure sensitivity of 1-pentyne over various palladium catalysts was studied under various conditions, and the effect of carbon dissolution in the crystal lattice near the surface was evidenced by high-resolution transmission electron microscopy.

Journal ArticleDOI
TL;DR: Hundreds of genes of both known and unknown function were significantly regulated at these time points of the symbiosis between Medicago truncatula roots and Sinorhizobium meliloti, shedding light on the complexity of coordinated gene regulation.
Abstract: Within the first 72 h of the interaction between rhizobia and their host plants, nodule primordium induction and infection occur. We predicted that transcription profiling of early stages of the symbiosis between Medicago truncatula roots and Sinorhizobium meliloti would identify regulated plant genes that likely condition key events in nodule initiation. Therefore, using a microarray with about 6,000 cDNAs, we compared transcripts from inoculated and uninoculated roots corresponding to defined stages between 1 and 72 h post inoculation (hpi). Hundreds of genes of both known and unknown function were significantly regulated at these time points. Four stages of the interaction were recognized based on gene expression profiles, and potential marker genes for these stages were identified. Some genes that were regulated differentially during stages I (1 hpi) and II (6-12 hpi) of the interaction belong to families encoding proteins involved in calcium transport and binding, reactive oxygen metabolism, and cytoskeleton and cell wall functions. Genes involved in cell proliferation were found to be up-regulated during stages III (24-48 hpi) and IV (72 hpi). Many genes that are homologs of defense response genes were up-regulated during stage I but down-regulated later, likely facilitating infection thread progression into the root cortex. Additionally, genes putatively involved in signal transduction and transcriptional regulation were found to be differentially regulated in the inoculated roots at each time point. The findings shed light on the complexity of coordinated gene regulation and will be useful for continued dissection of the early steps in symbiosis.