1,720,956 research outputs found
Individuazione e caratterizzazione di geni coinvolti nella nutrizione solfatica e nelle risposte a cadmio delle piante : loro possibile utilizzo per la costituzione di bioindicatori.
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Nuovi approcci per il miglioramento dell’efficienza d’uso dei nutrienti nelle piante : il caso dello zolfo
No full textL’efficienza con cui le piante usano un nutriente minerale (Nutrient Use Efficiency, NUE), definita come l’incremento di produzione determinato da un aumento del livello dell’elemento in seguito ad una sua somministrazione al suolo, è un tratto agronomico controllato da diversi geni e dalla loro interazione con l’ambiente. Approcci genetici in specie modello quali Arabidopsis thaliana e Oryza sativa hanno permesso di identificare geni o gruppi di geni strettamente associati al carattere NUE relativamente a macronutrienti quali N, P e K, ed utilizzabili come marcatori molecolari in programmi di selezione assistita. Nel caso dello zolfo, invece, esistono solo informazioni frammentarie. Attraverso approcci diversi sono stati identificati e caratterizzati in Arabidopsis geni e promotori coinvolti nelle risposte precoci della pianta a variazioni dello stato nutrizionale solfatico. Viene discussa la possibilità di utilizzare tali elementi per la costituzione di un bioindicatore transgenico in grado di segnalare rapidamente e in modo sito-specifico le necessità di zolfo della coltura, così da poter programmare interventi adeguati di fertilizzazione. La definizione della dose corretta e delle variabili spazio-temporali delle fertilizzazioni sono infatti elementi determinanti nel miglioramento dell’efficienza d’uso dei nutrienti minerali
Oxidative stress and senescence-like status of pear calli co-cultured on suspensions of incompatible quince microcalli
No full textThis work presents a simple in vitro system to study physiological, biochemical and molecular changes occurring in a pear callus (Pyrus communis L., cv. Beurré Bosc) grown in close proximity to spatially separated undifferentiated
homologous (pear) or heterologous (quince; Cydonia oblonga Mill., East Malling clone C) cells in its neighboring environment. After a 7-day co-culture period, the presence of heterologous cells produced negative effects on the pear callus, whose relative weight increase and adenylate energy charge decreased by 30 and 24%, respectively. Such behavior was associated with a higher O2 consumption rate (+125%) which did not seem to be coupled to adenosine triphosphate synthesis. Analyses of alternative oxidase and enzymatic activities involved in reactive oxygen species (ROS) detoxification strongly suggested that the higher O2 consumption rate, measured in the pear callus grown in the heterologous combination, may probably be ascribed to extra-respiratory activities. These, in turn, might contribute to generate metabolic scenarios where ROS-induced oxidative stresses may have the upper hand. The increase in the levels of 2-thiobarbituric acid reactive metabolites, considered as diagnostic indicators of ROS-induced lipid peroxidation, seemed to confirm this hypothesis. Moreover, reverse transcription polymerase chain reaction analysis revealed that the expression levels of a few senescence-associated genes were higher in the pear callus grown in the heterologous combination than in the homologous one. Taken as a whole, physiological and molecular data strongly suggest that undifferentiated cells belonging to a pear graft-incompatible quince clone may induce an early senescence-like status in a closely co-cultured pear callus
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
Sulfur metabolism and cadmium stress in higher plants
No full textPlant sulfur metabolism is deeply affected by cadmium (Cd) stress, mainly as a consequence of the activation of a wide range of adaptive responses involving glutathione (GSH) consuming activities. In fact, GSH not only acts as a direct or indirect antioxidant in mitigating Cd-induced oxidative stress, but also represents a key intermediate for the synthesis of phytochelatins (PCs), a class of cysteine-rich heavy metal-binding peptides involved in buffering cytosolic metal concentration. As a consequence, Cd exposure may result in a depletion of the cell GSH pools which in turn increases the plant demand for reduced sulfur compounds. In this condition the need for maintaining GSH homeostasis and an adequate PC biosynthesis rate is met by a general induction of enzyme activities directly or indirectly involved in sulfur metabolism. Transgenic plants overexpressing these enzymes exhibit a greater production of GSH and an increased Cd tolerance, confirming this pathway to be crucial for plant survival in metal polluted environments. In the present paper we analyze and discuss the biochemical and molecular mechanisms involved in the regulation of sulfate (the main sulfur source for plants) uptake and assimilation, and GSH synthesis during Cd detoxificatio
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
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