1,721,015 research outputs found
Proteomic changes in the roots of M4 grapevine rootstock in response to nitrate availability
No full textNitrogen (N) is an essential macronutrient for plants, but very little is known about the biochemical roles played by roots in N acquisition in grapevine (Vitis vinifera L.), an important grafted perennial fruit crop. In recent years, the grapevine rootstock M4 [(V. vinifera × V. berlandieri) × V. berlandieri] was the subject of physiological, transcriptomic and proteomic analysis that highlighted its higher tolerance to drought and salinity stress in comparison with other rootstocks. However, little information is available about its metabolic responses to the availability of nitrate (NO3-), the major form of N nutrient used by plants in agricultural soils. The aim of this study was to determine the metabolic events involved in NO3- acquisition in M4. In details, young M4 plants, grown in a hydroponic system, after a period of N starvation were maintained in the absence of N (control condition) or exposed to 10 mM NO3-. Firstly, the changes of some biochemical parameters (such as NO3-, sugar and amino acid contents) as well as the evaluation by Western blot analyses of the abundances of key enzymes (i.e. Nitrate Reductase and Glutamine Synthetase) were used to define the time course of the metabolic changes occurring in the first 30 h. Taken together, the results showed that root N metabolism significantly increased after 30 h of NO3- availability. To gain a better characterization, a proteomic analysis based on one-dimensional (1D) Gel Liquid Chromatography-Mass Spectrometry (GeLC-MS/MS) was conducted, comparing the root profiles in the control condition and after 30 h of NO3- induction. This approach allowed the identification of some hundreds of proteins, with high reliability and good reproducibility. Many of the proteins found to change in abundance were directly involved in NO3- uptake and assimilation, such as H+-ATPase, Nitrite Reductase and Glutamine Synthetase. According to the induction of N metabolism, some root enzymes involved in protein synthesis, folding and trafficking showed a relevant increment in abundances after 30 h of NO3- availability, while those involved in flavonoid metabolism generally showed a down-accumulation. Moreover, the results underlined the strict relationships between N nutrition, carbon metabolism and the metabolic pathways implicated in cell redox status. Overall, the proteomic analysis reveals that NO3- provision significantly affected the root proteome of M4 grapevine rootstocks, providing novel information about the biochemical pathways involved in N metabolism in this perennial plant. This study lays the bases for a better elucidation of the relations among N nutrition, rootstock/scion interactions and productivity in grapevine
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
Comparative proteomics of organelles in maize (Zea mays L.) roots in response to different availabilities of nitrate and ammonium
No full textNitrogen (N) is one of the main factors limiting agricultural productivity, especially in cereals such as maize (Zea mays L.), and nitrate (NO3-) and ammonium (NH4+) represent the predominant forms of N in agricultural soils. Plants are differently affected by the availability of these two N forms at morphological, physiological and metabolic levels, especially during the early stages of development. In particular, roots responses to different N availabilities involve the modulation of distinct metabolic pathways, the regulation of ion compartmentation and the balancing of cellular homeostasis. In this context, the strict coordination between the biochemical activities of cell organelles, among which mitochondria, plastids and vacuole, is crucial. Hence, subcellular proteomics represents a powerful method to study these metabolic interactions. The aim of this research was to study the roles of organelles in the adaptation to different N availabilities in maize roots, through the combination of physiological, metabolic and proteomic analyses. The research was conducted in roots of three-day-old maize plants, grown by hydroponic system, and exposed to different N availabilities: absence of N, 2.5 mM NO3-, 2.5 mM NH4+, 1.25 mM NO3- + 1.25 mM NH4+. This experimental design allowed to appreciate differences in plant growth and metabolic status, with variations in plant biomass accumulation and in the shoot/root ratios, in the contents of NO3- and NH4+ and metabolites, such as sugars and amino acids, and in the abundance of key enzymes in N assimilation (i.e. Nitrate Reductase and Glutamine Synthetase). Root organelles were enriched by differential centrifugation techniques and the sub-proteomic profiles were analysed by means of one- dimensional (1D) Gel Liquid Chromatography-Mass Spectrometry (1D GeLC-MS/MS). This approach allowed to identify and quantify a total of 365 proteins, showing, by means of bioinformatic analysis, a good degree of enrichment of the target proteomes (77.7%), and revealing that the 33% of the proteins were differently accumulated in the four conditions (one-way ANOVA, p ≤ 0.01). The results showed that the N forms induced different changes in abundance of proteins involved in the assimilation of N at the plastid level, in protein synthesis, in respiratory metabolism, and in the exchange of metabolites between organelles. Interestingly, some classes of mitochondrial carrier proteins, such as Mitochondrial dicarboxylate/tricarboxylate transporter (DTC), Mitochondrial phosphate carrier protein 3 and ADP/ATP carrier protein showed the highest abundance in NH4+-fed plants, highlighting a specific involvement of mitochondrion metabolism in root adaptations to this nutrient. Differently, the availability of NO3- affected the accumulation of some tonoplast proteins, such as aquaporins (TIP) and V-type proton ATPase subunits, and of some proteins involved in cell calcium network, providing new hints about the role of this nutrient both as osmolyte and metabolic signal. Overall, this research confirms the fundamental roles of roots in N acquisition and provides novel information about the responses induced by the different N nutrients in multiple sub-cellular compartments in young maize plants
An integrative approach to study the responses of Zea mays L. to organic nitrogen provided to roots in the form of amino acids
No full textAlthough the capacity to take up organic nitrogen (N) in the form of amino acids is widespread among plants, their relevance for N nutrition in crops has been little investigated compared to inorganic N sources. In the last years, several studies have pointed out that distinct amino acids exert different effects on plant morphology and physiology. However, less is known about their effects on plant metabolism, especially when supplied to the roots at composition and concentration mimicking soil conditions. In this respect, this work aimed to investigate the capacities of crops, such as maize (Zea mays L.), to utilize amino acids as N nutrients through an approach that integrates morphological, physiological, biochemical and proteomic evaluations. Maize seedlings were grown by a hydroponic system for three days in the absence of N and then were provided for further four days with 250 μM of a mixture of eight amino acids [Glutamic acid (50 μM), Glutamine (50 μM), Glycine (50 μM), Alanine (50 μM), Aspartic acid (12.5 μM), Arginine (12.5 μM), Lysine (12.5 μM) and Threonine (12.5 μM)], or with 250 μM of inorganic N in the form of nitrate. Plants were analyzed after five and seven days of hydroponic growth to follow both early responses and later metabolic adjustments. Plants supplied with amino acids continued to grow over the experiment, although less than those supplied with nitrate. Therefore, plants utilized both the N sources for growth. In detail, amino-acid treated plants were characterized by a decreased root/shoot ratio and a shorter but thicker root system than nitrate-treated plants. The responses at a nutritional and metabolic level significantly differed, as suggested by changes in the plant content of nitrate, ammonium and key metabolites such as reducing sugars and sucrose. The LC-ESI-MS analysis of amino acid composition in roots, xylem sap and leaves revealed that the roots of plants supplied with amino acids showed an upsurge in the levels of uncharged and basic amino acids. Interestingly, glutamine and alanine were the major amino acids translocated through xylem sap for both the nutritional conditions, while the proportion of amino acids in leaves was more constant over time. Overall, these results highlight the different roles played by roots and leaves in response to N inputs and suggest that roots perceived and adapted promptly to the kind of N available and influenced N translocation to the shoot. In order to clarify the meaning of these metabolic adjustments, large-scale analysis of the total proteome fraction of roots and leaves based on one-dimensional Gel Liquid Chromatography-Mass Spectrometry (1D GeLC-MS/MS) is ongoing. This study will improve the knowledge about plant responses to different N inputs and plant metabolic use of amino acids, providing information that could be useful for enhancing the sustainability of crop production
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
- …
