1,721,042 research outputs found
Phytochelatin synthase 1 regulates iron homeostasis in Arabidopsis thaliana
No full textPhytochelatin synthases (PCS, EC 2.3.2.15) are cytosolic enzymes, constitutively expressed in the genome of different organisms including Schizosaccharomyces pombe (1), Caenorhabditis elegans (2,3), algae and plants (4). PCS have been explicitly studied with respect to their role and mechanism of action towards heavy metal detoxification (e.g. essential heavy metals such as zinc (Zn) as well as toxic such as cadmium (Cd) (5). Based on studies of Arabidopsis thaliana phytochelatin synthase 1 (AtPCS1), it is recognized that PCS catalyse the formation of thiol rich oligomers, phytochelatins (PCs), from glutathione (GSH) and related thiols in the presence of metal ions (6).
Moreover: i) AtPCS1 is involved in the catabolism of GSH-conjugates (7); ii) AtPCS1 is required for pathogen-triggered callose deposition (8); iii) its mRNA is upregulated by a mimic of eubacterial flagellin (8); iv) AtPCS1 expression might be not upregulated by heavy metal toxicity (9), but its transcript abundance in roots increases by deficiency of the micronutrient iron (Fe) (10); v) physiological (homeostatic) Fe concentrations activate the in vitro activity of PCS even in basal land plants (11).
The main goal of this study was to determine the AtPCS1-driven response towards Fe deficiency and to establish whether and how AtPCS1 is involved in Fe homeostasis. To do so, we compared the growth, Fe concentration, and the expression of Fe transporter genes in roots and shoots of the A. thaliana cad1-3 mutant lacking functional AtPCS1 and transgenic plants overexpressing AtPCS1 (AtPCS1-OE) vs. wild-type, all grown either under Fe-sufficient or deficient conditions. We found that the cad1-3 mutant accumulated less Fe in roots and was significantly more sensitive to Fe deficiency than wild-type plants. By contrast, AtPCS1-OE lines were more tolerant to Fe deficiency than cad1-3 and wild-type plants. These results were consistent with the expression of Fe transporter genes in different plant lines. A mechanistic model of the role of AtPCS1 in Fe homeostasis will be proposed and discussed
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
Effects of phytochelatin synthase on the secondary metabolism of Arabidopsis thaliana plants
No full textPhytochelatin synthase (PCS, EC 2.3.2.15) is a constitutively expressed cytosolic enzyme, found in a number of prokaryotes and eukaryotes, and amongst plants, preliminarily characterized in charophytes as well as in basal land plants (Degola et al., 2014; Petraglia et al., 2014).
At first, PCS was found to be involved in metal detoxification mechanisms (Grill et al., 1989). Nonetheless, the fact that PCS is ubiquitously expressed in the plant clade and in many other organisms, even in the complete absence of toxic metal(loid)s, would lead us to postulate other possible function(s) other than mere metal(loid) detoxification. In fact, PCS appears to be also involved in the catabolism of glutathione-conjugates (Beck et al., 2003), in camalexin production (Su et al., 2011) and in callose formation (Clay et al., 2009).
To better understand the functional roles of the enzyme besides metal detoxification, our work was aimed first at delineating Arabidopsis thaliana (At) metabolomics, in control and in Cd-exposed plants (shoots and roots). At this purpose, all metabolites from At wild-type (wt), PCS1 knockout mutant (cad1-3) and PCS-overexpressing mutant (AtPCS1-OE) were compared.
First of all, a different accumulation of glutathione (GSH), the substrate of PCS, was detected amongst the three plant lines. Indeed, the evidence of a higher GSH content found in cad1-3 mutants and a minor GSH content in AtPCS1-OE plants, suggests an important role of PCS to maintain GSH homeostasis. Furthermore, an accumulation of 4-methoxy-indol-3-ylmethylglucosinolate was detected in cad1-3 plants grown in the absence/presence of Cd. This glucosinolate is involved in callose production (Clay et al., 2009) and thus could contribute to defense mechanisms against pathogen attacks. Callose staining and pathogen assay experiments in our mutants showed that PCS protects plants against metal toxicity and also contributes to callose deposition; moreover, the PCS expression is essential to the resistance mechanism raised against the bacterium Pseudomonas syringae DC3000.
In addition, varying contents of flavonols were found among the three plant lines. An increase of kaempferol was measured in shoots and quercetin in roots of cad1-3 mutants, whilst lower amounts were found in AtPCS1-OE plants, compared with wt. Kaempferol and quercetin play several functions in the plant cell, among which the regulation of auxin efflux. Consequently, the content of indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), indole-3-carboxylic acid (ICA) and indole-3-acetic acid methyl ester (MeIAA) was altered in mutant plants.
Not least, different levels of lignin precursors were found among the three plant lines exposed or not to Cd. As expected, stretch experiments proved a difference in terms of force/pressure required for breaking stems of the three plant lines, even grown in control conditions. Therefore, this work has highlighted for the first time potential new roles of AtPCS on cell wall remodeling, metabolism of phenilpropanoids, as well as modulation of auxin in planta distribution
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
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