102,185 research outputs found
Diatom/copepod interactions in plankton: The indirect chemical defense of unicellular algae
No full textMax-Planck-Institut fur Chemische Okologie, Hans-Knoll-Strasse 8, 07745 Jena, Germany. [email protected] Numerous coexisting species can be observed in the open oceans. This includes the complex community of the plankton, which comprises all free floating organisms in the sea. Traditionally, nutrient limitation, competition, predation, and abiotic factors have been assumed to shape the community structure in this environment. Only in recent years has the idea arisen that chemical signals and chemical defense can influence species interactions in the plankton as well. Key players at the base of the marine food web are diatoms (unicellular algae with silicified cell walls) and their main predators, the herbivorous copepods. It was assumed that diatoms represent a generally good food source for the grazers but recent work indicates that some species use chemical defenses. Secondary metabolites, released by these algae immediately after wounding, are targeted not against the predators themselves but rather at interfering with their reproductive success. This strategy allows diatoms to reduce the grazer population, thereby influencing the marine food web. This review addresses the chemical ecology of the defensive oxylipins formed by diatoms and the question of how these metabolites can act in such a dilute environment. Aspects of biosynthesis, bioassays, and the possible implications of such a chemical defense for the plankton community structure are also discussed.LEC
Unprecedented lipoxygenase/hydroperoxide lyase pathways in the moss Physcomitrella patens
No full textLEC
Phospholipase A(2) activity triggers the wound-activated chemical defense in the diatom Thalassiosira rotula
No full textMax-Planck-Institut fur Chemische Okologie, Winzerlaer Strasse 10, D-07745 Jena, Germany. [email protected] The activation of oxylipin-based chemical defense in the diatom Thalassiosira rotula is initiated by phospholipases that act immediately after cell damage. This lipase activity is responsible for the preferential release of free mono- and polyunsaturated fatty acids. Among these, eicosatetraenoic- and eicosapentaenoic acid are further converted by lipoxygenases to reactive defensive metabolites such as the antiproliferative alpha,beta,gamma,delta-unsaturated aldehydes 2,4-decadienal and 2,4,7-decatrienal. We show that mainly saturated free fatty acids are present in the intact diatom T. rotula, whereas the amount of free polyunsaturated eicosanoids is drastically increased in the first minutes after wounding. Using fluorescent probes, the main enzyme activity responsible for initiation of the aldehyde-generating lipase/lipoxygenase/hydroperoxide lyase cascade was characterized as a phospholipase A2. All enzymes involved in this specific defensive reaction are active in seawater over several minutes. Thus, the mechanism allows the unicellular algae to overcome restrictions arising out of potential dilution of defensive metabolites. Only upon predation are high local concentrations of aldehydes formed in the vicinity of the herbivores, whereas in times of low stress, cellular resources can be invested in the formation of eicosanoid-rich phospholipids. In contrast to higher plants, which use lipases acting on galactolipids to release C18 fatty acids for production of leaf-volatile aldehydes, diatoms rely on phospholipids and the transformation of C20 fatty acids to form 2,4-decadienal and 2,4,7-decatrienal as an activated defense.LEC
Bibliographie Hilarion G. Petzold 1958 – 2009 mit Anhang als Einführung
No full textDieses Archiv enthält die Gesamtbibliographie der Werke des Autors nebst einiger Texte „Über H. G. Petzold“ im Schlussteil der Bibliographie sowie einen Anhang mit einer Einführung in die Architektur des Werkes in seinem wissenslogischen Aufbau als Ausarbeitung seines „Tree of Science Modells“ (2007).This archive contains the complete bibliography of the author and some texts about H. G. Petzold, moreover an epilogue with an introduction to the architecture of the works in its epistemological structure and composition and as an elaborations of Petzold’s „Tree of Science Modell (2007).https://www.fpi-publikation.de/polyloge/01-2009-petzold-h-g-gesamtbibliographie-h-g-petzold-1958-2009-updating-november2009/peerReviewedpublishedVersio
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
A multifunctional lipoxygenase with fatty acid hydroperoxide cleaving activity from the moss Physcomitrella patens
No full textA complex mixture of fatty acid-derived aldehydes, ketones, and alcohols is released upon wounding of the moss Physcomitrella patens. To investigate the formation of these oxylipins at the molecular level we isolated a lipoxygenase from P. patens, whic
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3346: Samuel G. Freedman, author, 2013
No full textPhotograph of author Samuel G. Freedman, at NT Daily Slash meeting in the Mayborn School of Journalism at UNT
The Right to Strike under the United States Constitution: Theory, Practice, and Possible Implications for Canada
No full textAnswering critics of the Canadian Supreme Court's judgment in B.C. Health, the author argues that the Court laid the foundation for a principled and durable doctrine protecting constitutional labour rights, one that goes directly to the heart of the matter — the inequality of workers’ power in the employment relation. In the author’s view, two paths could lead from B.C. Health to the recognition of Charter protec- tion for a right to strike: one that treats the right as an accessory to col- lective bargaining, and one that upholds the right directly on the basis of the Charter values of equality and participation. The author supports the latter approach, contending that constitutional rights should be defined in relation to fundamental values, in a way that is not contingent on time-bound or fact-sensitive assessments about the role of strikes within a particular collective bargaining regime. Although a Charter right to strike may involve the courts in difficult choices about when to defer to legislative policy decisions, and courts may lack the institutional capac- ity to deal effectively with labour law issues, the author points out that judges can look to ILO standards for expert guidance. Noting that the U.S. experience in this area might be of considerable use to Canadians, the author concludes by providing an overview of American case law concerning a constitutional right to strike.Peer reviewe
Dasycladus vermicularis Krasser 1898
No full text<i>2.1. Sulfated metabolites of D. vermicularis</i> <p> <b>⇑</b> Corresponding author. <i>E-mail address:</i> [email protected] (G. Pohnert).</p> <p> Three candidate molecules for which sulfatation was indicated by the presence of a fragment of [M–H–80] – in the mass spectrum were detected by UPLC–MS/MS measurements in extracts of <i>D. vermicularis</i>. The metabolite with a mass of 273 [M–H] – and a fragment with <i>m</i> / <i>z</i> = 193 could readily be assigned to dihydroxycoumarin sulfate (Fig. 1) based on previous results and co-injection with a synthetic standard (Welling et al., 2009). For identification of the two unknown potentially sulfated metabolites (<i>m</i> / <i>z</i> = 217 [M–H] – and 231 [M–H] –, respectively) synthetic standards were prepared. Based on mass spectra and polarity in UPLC–MS (Fig. 2A, D and F) we selected 4-(sulfooxy)benzoic acid (SBA) and 4-(sulfooxy)phenylacetic acid (SPA) as likely candidates. After estimation of the content of the metabolites in the algal extract, co-injection experiments with algal extract and the synthetic standards were performed (Fig. 2C and E). Peak symmetry was important since the short retention times and strong solvent effects of the samples required a rigorous quality control of co-eluting peaks. SBA showed the same retention time and mass spectrum to the first sulfated metabolite in the <i>D. vermicularis</i> extract. When added in co-injection experiments, an increase of intensity of the first signal was observed (Fig. 2C). The mass spectrum remained unaffected by the co-injection. The <i>ortho</i> - and <i>meta</i> -isomers of (sulfooxy)benzoic acid eluted at different retention times (data not shown). The same procedure was applied for co-injection of SPA (Fig. 2E). No significant change in peak symmetry was observed upon addition of SBA or SPA, which unambiguously confirms the identity of the natural and synthetic products. Besides the occurrence as catabolic products in mouse urine, these metabolites have to our knowledge not been reported as natural products before (Manna et al., 2011; van der Hooft et al., 2012).</p>Published as part of <i>Kurth, Caroline, Welling, Matthew & Pohnert, Georg, 2015, Sulfated phenolic acids from Dasycladales siphonous green algae, pp. 417-423 in Phytochemistry 117</i> on page 417, DOI: 10.1016/j.phytochem.2015.07.010, <a href="http://zenodo.org/record/10486436">http://zenodo.org/record/10486436</a>
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