1,721,019 research outputs found
Plant Esterified Oxylipins: Molecular Characterization and Structure-Function Relationships
No full textPlant oxylipins including free and esterified oxylipins are structurally diverse molecules produced following fatty acid oxidation. Free oxylipins regroup various compounds with important functions in plant defence and developmental processes. Notably, jasmonic acid as well as its derivatives and some of its precursors are a family of phytohormones largely studied for their biological activities. On the other hand, esterified oxylipins have been much less studied but recent research showed their possible ubiquity in plants, as well as their probable involvement in plant defence and developmental mechanisms. Arabidopsides are a particular class of esterified oxylipins, and more precisely of oxidized galactolipids. Those were firstly described in A. thaliana but were also highlighted in other plant species and families. Interestingly, the oxidized fatty acyl chain of those molecules is either 12-oxo-phytodienoic acid or dinor-12-oxo-phytodienoic acid, both being intermediates in jasmonic acid synthesis. 12-oxo-phytodienoic acid is also a signal molecule implied in the modulation of plant defence gene expression. It has therefore been hypothesized that esterified oxylipins may either have direct functions or be used as a pool of free oxylipins. The latter may then act directly or be used for the synthesis of jasmonic acid. In the first part of the present thesis, a literature review discusses esterified oxylipin diversity, biosynthesis and potential functions.
The second part of this thesis describes the extraction and purification of the 5 main arabidopside molecules (A, B, D, E and G) produced by A. thaliana in stress conditions. In that way, following the induction of arabidopside production and the extraction of lipids, the latter were fractionated on silica column. Arabidopsides were finally purified by preparative-HPLC. An analytical method was then developed and validated to detect and quantify those molecules in leaf samples. Lipids were extracted and the polar lipid fraction was purified by solid phase extraction before being analysed by HPLC-MS. External calibration with purified arabidopside standards was chosen for arabidopside quantification. The method selectivity, limits of detection and quantification, intra-day and inter-day precision and accuracy, matrix effects and recoveries were determined. As arabidopsides are not commercially available, the obtention of purified molecules and the validation of the quantification method by HPLC-MS were used in the next part of this work to more deeply explore the functions of those understudied molecules.
As arabidopsides are biosynthesized from chloroplast membrane galactolipids, their precise localization among the different chloroplast compartments was determined in the third part of the present thesis. Results showed that arabidopsides are mainly found in thylakoid membranes but that the more polar forms are also present in the chloroplast stroma. As chloroplasts are largely implied in plant stress responses, and notably through the synthesis of reactive oxygen species and phytohormone precursors, we studied the impact of biotic stress induced by the recognition of the avirulence protein AvrRpm1 from Pseudomonas syringae on the structure of the chloroplasts of A. thaliana. Electron microscopy results showed that chloroplast structure is largely affected in stress conditions. In addition, thylakoid membrane fluidity was increased in such conditions, which could be due to arabidopside formation in those membranes. To better understand how arabidopside formation modifies thylakoid membrane properties upon stress, complementary biophysics and bioinformatics methods were used. Results showed that arabidopsides display very different interfacial properties than non-oxidized galactolipids which are found in thylakoid membranes in physiological conditions. Moreover, it was highlighted that arabidopsides A, B and D can interact with model membranes, leading to their destabilization. Results then suggest that arabidopside formation in stress conditions probably modify thylakoid membrane properties, which could affect their functions.
Globally, this work has contributed to a better knowledge of arabidopsides produced by A. thaliana in terms of quantification, localization in planta and effects on thylakoid membranes. It therefore provides new elements for a better understanding of the potential functions of these molecules, notably in the field of plant immunity
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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