1,720,962 research outputs found
Putative ornithine decarboxylase activity in Arabidopsis thaliana: Inhibition and intracellular localisation
No full textIn this work we studied putative ornithine decarboxylase activity (ODC, EC 4.1.1.17) in leaves of Arabidopsis thaliana L. (ecotype Columbia) plants at non-flowering stage (about 21 d of culture). Putative ODC activity was higher in the particulate than in the soluble fraction and activity was pH-dependent, increasing linearly with the pH. Inclusion of 10 mM arginine in the assay showed that the incidence of ornithine transcarbamoylase activity (EC 2.1.3.3) accounted for about 35% in the particulate fraction, but that its contribution was negligible in the soluble fraction. Increasing concentrations of the irreversible inhibitor alpha-difluoromethylornithine (DFMO) progressively inhibited putative ODC activity with a 40% inhibition at 20 mM DFMO. Taking into consideration the incidence of ornithine transcarbamoylase activity, the total inhibition of putative ODC activity was of about 75%. Fractionation experiments permitted measurement of putative ODC activity in the nuclei- and chloroplast-enriched fractions. The assays performed on membranes and stromal fractions isolated from gradient purified chloroplasts showed that the enzyme activity was associated almost totally with the plastid membranes
Effects of spermidine synthase overexpression on polyamine biosynthetic pathway in tobacco plants
Full text linkTransgenic tobacco plants overexpressing the Datura stramonium spermidine synthase
(EC 2.5.1.16) cDNA were produced in order to understand the role of this gene in the
polyamine metabolism and in particular in affecting spermidine endogenous levels. All
the analysed transgenic clones displayed a high level of overexpression of the
exogenous cDNA with respect to the endogenous spermidine synthase. No relationship
was detected between the mRNA expression level of S-adenosylmethionine
decarboxylase (SAMDC, EC 4.1.1.50), which did not change between the negative
segregant control and the transgenic plants, and spermidine synthase, suggesting the
existence of an independent regulatory mechanism for transcription of the two genes.
The determination of enzyme activities indicated an increased spermidine synthase
and S-adenosylmethionine decarboxylase activity, with the last being mainly
recovered in the particulate fraction. ODC (ODC, EC 4.1.1.17) was the most active
enzyme and its activity was equally distributed between the soluble and the
particulate fraction, while ADC (ADC, EC 4.1.1.19) activity in the transgenic plants did
not particularly change with respect to the controls. In comparison to the controls,
the transformed plants displayed an increased spermidine to putrescine ratio in the
majority of the clones assayed, while the total polyamine content remained almost
unchanged. These findings suggest a high capacity of the transformed plants to tightly regulate polyamine endogenous levels and provide evidence that spermidine synthase
is not a limiting step in the biosynthesis of polyamines
Jasmonate and Na-orthovanadate promote resveratrol production in Vitis vinifera cv. Barbera cell cultures
No full textHere the effect of jasmonic acid, methyljasmonate and Na-orthovanadate on the production of resveratrol was studied in Vitis vinifera cv. Barbera cell suspension cultures.
• Na-orthovanadate at 0.1 mM and 1 mM concentration was efficient in promoting the production and/or accumulation and release in the culture medium of cis-resveratrol while trans-resveratrol levels were not affected by this treatment.
• Methyljasmonate was highly effective in stimulating both trans- and cis-resveratrol endogenous accumulation, as well as their release into the culture medium. Cis-resveratrol was absent or detected in very low amounts in the controls. Jasmonic acid was less efficient than methyljasmonate in promoting endogenous resveratrol
accumulation, but it stimulated the release in the culture medium especially of cis-resveratrol.
• Gel analysis was performed on control and 10 μM MeJA treated cell suspensions. Results showed an up-regulation of the stilbene synthase demonstrating that MeJA stimulated the synthesis ex-novo of this protein
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
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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