1,720,972 research outputs found
Integration of plastids in the plant calcium signalling network in response to environmental stimuli.
Full text linkTransient elevations in intracellular free Ca2+ concentration are known to mediate plant responses to a wide variety of abiotic and biotic stimuli. To elucidate the contribution of plastids to Ca2+ homeostasis and signalling in the plant cell, we generated Arabidopsis thaliana lines stably expressing the bioluminescent Ca2+ reporter aequorin targeted to different chloroplast subcompartments, i.e. the outer envelope, the stroma, the thylakoid membrane and the thylakoid lumen. Ca2+ measurements in response to environmental stimuli were carried out in entire seedlings, as well as in cell suspension cultures, obtained from in vitro dedifferentiation of Arabidopsis explants. Monitoring of Ca2+ dynamics allowed to dissect stimulus-specific Ca2+ signals in amyloplasts and chloroplasts, as well as the occurrence of dark-induced intraplastidial Ca2+ fluxes, characterized by unique kinetic parameters. To get insights into the homeostatic mechanisms allowing for chloroplast Ca2+ fluxes, a mutant line lacking a putative plastidial Ca2+-permeable transporter was transformed with the construct encoding the stroma-targeted aequorin chimera. The obtained results shed new light on the complex network underlying the Ca2+-mediated transduction of environmental stimuli in plants at an intracellular level. This complex kit of chloroplast-targeted aequorin probes turned out to be a valuable tool for the monitoring of organellar Ca2+ dynamics during signal transduction. In the last part of the work the ability of Chlamydomonas reinhardtii, a unicellular freshwater/soil green alga, to evoke intracellular Ca2+ changes ([Ca2+]) in response to different environmental stimuli was considered. As there is no evidence in the literature about environmental stimuli that trigger cytosolic [Ca2+] variations in Chlamydomonas, the first step had necessarily to deal with the identification of environmental cues evoking cytosolic [Ca2+] elevations in the microalga. Chlamydomonas cells, loaded with the Ca2+-responsive fluorescent dye Oregon Green-BAPTA, were challenged with stimuli previously used in this work on Arabidopsis. Moreover, the alga was also challenged with a hypoosmotic shock, that resulted to trigger cytosolic [Ca2+] elevations, and the nature of the observed dynamics was investigated. Taken together, the obtained results indicate that some aspects of Ca2+ signalling do not appear to be conserved between the green alga Chlamydomonas and the higher plant Arabidopsis, but other elements in Ca2+-mediated responses to osmotic shocks are similar. These differences may be due to the different Ca2+ signalling toolkits found in plants and algae and/or to the different physiology of these model organisms, both belonging to the Viridiplantae clade. Investigation on the Ca2+ handling mechanisms operating in different photosynthetic organisms of phylogenetic interest may shed new light on the evolutionary history of the Ca2+ signalling toolkit
Evaluation of new aequorin-based calcium probes for the monitoring of calcium dynamics and cross-talk between plastids and endoplasmic reticulum in plant cells
No full textInternalizzazione di sonde proteiche fluorescenti e bioluminescenti mediata dal peptide TAT nel fungo micorrizico arbuscolare Gigaspora margarita
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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
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