1,721,069 research outputs found
Effect of decreasing levels of Fe availability on S assimilation pathway in durum wheat (Triticum durum L.) seedlings
No full textIron is an essential element required for many crucial cellular functions. Studies in many
different organisms have shown that Fe deficiency induces several responses including
increased uptake of Fe from the environment. In plants, it is achieved through the
activation of several components of the Strategy I and II Fe uptake system. Wheat belongs
to Strategy II plants and therefore cope with Fe deficiency by increasing both the synthesis
and secretion of phytosiderophores (PS), and the uptake of Fe-PS complexes. Besides the
processes described for Strategy II, sulfate assimilation pathway is known to be induced
upon Fe deprivation in various plant species (maize, barley and wheat), most likely
because PS are derived from nicotianamine, whose precursor is methionine.
Aim of this study was to investigate if sulfate assimilation rate could be modulated in an Fe
concentration-dependent manner. To this purpose, durum wheat seedlings were grown
hydroponically for eight days with Fe(III)-EDTA concentrations ranging from 0 to 75 μM.
The amount of PS released by roots gradually increased with decreasing external Fe
concentrations, this result being correlated to the increase in root thiol concentration. This
was supported by roots showing higher activity of both ATP sulfurylase and Oacetylserine(thiol)lyase, the first and the last enzyme of S metabolism, respectively.
These preliminary results suggest that the capability to induce sulfate assimilation pathway
when plants sense the onset of Fe limitation seems to correlate with the general S use
efficiency of a plant species as an ecological adaptation to Fe deficiency
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
LOW-MOLECULAR-WEIGHT HUMIC SUBSTANCES STIMULATE H+-ATPASE ACTIVITY OF PLASMA-MEMBRANE VESICLES ISOLATED FROM OAT (AVENA-SATIVA L) ROOTS
No full textThe effect of 5 KDa (high molecular weight, HMW) humic fractions on transport activities of isolated plasma membrane vesicles was studied. The K+-stimulated component of the ATP-hydrolyzing activity was considerably increased by LMW humic substances at concentrations ranging from 0.075 mg org CL-1 to 1 mg org CL-1. The stimulation was still evident when the detergent Brij-35 was added in the assay mixture, indicating a direct effect of LMW humic substances on plasma membrane ATPase activity. The LMW humic fraction stimulated ATP-dependent intravesicular H+-accumulation with a pattern similar to that recorded for ATP hydrolysis. LMW humic substances induced also an increase in passive membrane permeability to protons, as revealed by following the dissipation of an artificially imposed pH gradient. Membrane permeability to anions, as measured by the anion-dependent active proton accumulation was affected by LMW humic substances. In the presence of NO3- these molecules clearly enhanced proton transport, while Cl--dependent activity was almost unaffected, thus suggesting a specific action of LMW humic fraction on transmembrane NO3- fluxes. On the other hand, HMW humic substances decreased the passive permeability to protons and reduced the anion-dependent intravesicular H+-accumulation. The results suggest that the stimulatory effect of soil humic substances on plant nutrition and growth might be, at least in part, explained on the basis of both direct action of LMW humic molecules on plasma membrane H+-ATPase and specific modification of cell membrane permeability
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
Isolation and preliminary characterization of ATPase from olive calli grown at different auxin/cytokinin ratio
No full textRevision surgery for failures of lumbar arthrodesis with fusion cages. Vol 10, Supp 1, Aug. 2001
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