1,721,164 research outputs found
Plant Volatiles in Defence.
No full textPlant odours are the most ubiquitous volatiles in nature. This chapter deals with the biochemistry and molecular biology of plant volatiles that are emitted from vegetative tissues during pathogen- or herbivore-induced stress and the contribution of these volatiles to plant defences. While mechanical tissue wounding causes the non-specific release of volatiles, herbivore-specific elicitors from their saliva distinctly alter the volatile signature. These volatiles acquired diverse roles in ecological interactions. Firstly, they can be toxic to, or repel conspecific or other herbivores from already infested plants. This function is referred to as ‘direct defence’. Secondly, volatiles function as prey-associated signals for foraging carnivorous arthropods. This is referred to as ‘indirect defence’. Finally, volatiles elicit metabolic changes in unattacked neighbouring plants resulting in priming and induction of defences already before herbivores have arrived. This is referred to as ‘plant-plant communication’. Although volatile production by native plants and crops is highly variable under different growth conditions and during development, its function in direct and indirect defences is remarkably robust. With the current state of knowledge, it is now possible to manipulate these direct and indirect defences through breeding or transgenic approaches. Taken together, plant volatiles play profound roles in plant-herbivore and plant-pathogen interactions and are promising targets for improved crop protection
Cross-talk in plant defense signaling: Antagonism between salicylate and jasmonate pathways in Arabidopsis
No full textPlants are equipped with an array of defense mechanisms to protect themselves against herbivorous insects and microbial pathogens. Some are pre-existing while others are only activated upon insect attack or pathogen invasion. However, induced defense responses entail fitness costs. Therefore, plants possess elaborate regulatory mechanisms that efficiently coordinate activation of attacker-specific defenses. A major focus in plant defense signaling research is to uncover key mechanisms by which plants tailor their responses to different attackers, and to investigate how plants cope with simultaneous interactions with multiple aggressors. The phytohormones salicylic acid (SA) and jasmonic acid (JA) play a major role in the regulation of induced defense mechanisms against biotrophic pathogens and insect herbivores, respectively. Cross-talk between SA and JA defense signaling pathways is thought to allow fine-tuning of the defense response to the attacker encountered. In Arabidopsis, pharmacological experiments revealed that SA exerts a strong antagonistic effect on JA-responsive genes, such as PLANT DEFENSIN1.2 (PDF1.2), indicating that the SA pathway can be prioritized over the JA pathway. This antagonistic effect of SA on JA signaling is a robust phenomenon: It is conserved among Arabidopsis accessions, and JA-responsive gene expression is readily suppressed by SA for several days, even when triggered by very low doses of SA. Time interval studies revealed that SA has a window of opportunity to suppress MeJA-responsive gene expression, and that this time interval correlates with the SA-induced redox change in the plant tissue. Thus, redox modulation is likely to play a central role in the regulatory mechanism underlying SA/JA cross-talk. Analysis of the Arabidopsis mutant npr1, impaired in SA signal transduction, revealed that the antagonistic effect of SA on JA signaling requires the regulatory protein NPR1. Nuclear localization of NPR1, which is essential for SA-mediated defense gene expression, is not required for suppression of JA-responsive genes, indicating that cross-talk between SA and JA is modulated through a function of NPR1 in the cytosol. TGA transcription factors are similarly required for both SA-dependent gene expression and SA-mediated suppression of JA signaling. However, TGA factors are unlikely to exert their effect through direct interaction with the promoter of JA-responsive genes such as PDF1.2, as removal of the TGA binding site in this promoter did not affect cross-talk. Promoter analysis of SA-suppressed, MeJA-inducible cross-talk genes revealed enrichment of the I box and the GCC box motif. Site-directed mutagenesis of the I box motif in the PDF1.2 promoter did not affect suppression of this gene by SA, indicating that the I box is not essential in mediating cross-talk. The role of the GCC box in cross-talk regulation should be further elucidated. This motif is required for MeJA-responsiveness in the PDF1.2 promoter, and thus provides an attractive target for SA-mediated suppression. Collectively, this work provides novel insight into how plants regulate their defense response upon attack by multiple aggressors, and may prove valuable for the development of novel strategies for crop protection
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
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