1,720,999 research outputs found
Analysis of the peroxisomal nitric oxide content and root architecture in Arabidopsis seedlings grown under cadmium-induced stress
No full textNitric oxide (NO) is a free radical involved in plant development and in response to stress conditions. Peroxisomes are organelles which are known to be a NO source [1]. Cadmium (Cd) pollution is a factor limiting the growth and productivity of important crops and is also a risk for human health throughout the food chain. It is known that, for a proper plant root development, both under physiological and stress conditions, a cross-talk between hormones and specific contents of ROS and NO is needed [1]. Catalase (CAT) is an antioxidant enzyme found in peroxisomes which, by catalyzing the H2O2 into water and oxygen, contributes to regulate ROS content in plant cells. The goal of the study was to highlight how Cd affects NO cellular content, CAT activity, peroxisomes distribution and root development in Arabidopsis thaliana. To this, 14-day-old transgenic plants expressing cyan fluorescent protein (35S:CFP) through the addition of the peroxisomal targeting signal 1 (PTS1), which enables peroxisomes to be visualized in vivo, were grown in the presence of 60 μM CdCl2. Moreover, using a cell-permeable NO specific fluorescent probe by confocal laser scanning microscopy (CLSM), we studied how Cd affects NO root content. Data indicate that Cd altered both Arabidopsis root morphology and NO distribution. The pollutant increased the length and density of lateral roots (LRs), whereas reduced the primary root (PR) length. In addition, Cd increased NO levels in the LRs and decreased it in the PR. PTS1 signal was changed by Cd only in the PR, showing a decrease of peroxisomes distribution and intensity. Furthermore, biochemical assays indicated that Cd negatively affects CAT activity. Our findings suggest that Cd affects H2O2 metabolism and NO content by acting on peroxisomes activity, leading to root architecture alteration and confirming the role of these organelles in the mechanisms of response against this pollutant
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
Histological study of embryogenesis and organogenesis from anthers ofVitis rupestris du Lot cultured in vitro
No full textAnthers of Vitis rupestris du Lot were cultured in vitro at the uninucleate stage of the microspore, in order to investigate the histology of embryogenic and organogenic processes in this genotype. Microspores divided in the anther loculi resulting in the formation of globular structures with a ruptured exine. Somatic embryogenesis and, occasionally, caulogenesis and rhizogenesis occurred in calli produced from all anther tissues except the endothecium. The initial cell of the embryoid was surrounded by a jacket layer when situated deep within the callus. When the embryoid's initial cell was situated in the peripheral callus, a cutinized wall was present and the three-celled proembryoid was almost always segmented, showing the same embryonal type as the zygotic proembryo. Root differentiation and elongation and cap differentiation occurred during the growth phase in liquid medium. The mature root was diarch and contained cells with calcium-oxalate raphides, as seen in vivo. No starch or tannin deposition was ever observed in the mature embryoids
De Novo Root Formation in Tobacco Thin Layers is Affected by Inhibition of Polyamine Biosynthesis
No full textThe effect of various inhibitors of polyamine biosynthesis on free and bound polyamine accumulation and on rhizogenesis was followed in thin layers excised from the stem of Nicotiana tabacum L. cv. Samsun. Trichloroacetic acid-soluble (TCA-soluble) free, TCA-soluble bound, and TCA-insoluble bound putrescine and spermidine accumulated throughout the culture period in control explants, reaching a peak on days 15-18. All the inhibitors tested depressed the rhizogenic process, though to a different extent, while leaving most of the explants viable. DL-alpha-difluoromethylornithine plus DL-alpha-difluoromethylarginine (DFMO + DFMA), specific irreversible inhibitors of ornithine- and arginine decarboxylases, respectively, almost totally inhibited rhizogenesis and polyamine accumulation. DFMO alone allowed a certain concentration of putrescine and spermidine to accumulate and rhizogenesis to occur in 20% of the explants. Cyclohexylamine (CHA), a competitive inhibitor of spermidine synthesis, did not have a strong inhibitory effect on root formation but depleted free and bound spermidine almost totally. Methylglyoxal-bis(guanyl)hydrazone (MGBG), an inhibitor of spermidine synthesis, caused a strong reduction in rhizogenesis but an accumulation of polyamines at the end of the culture period. No noticeable reversion of the rooting inhibition was observed by supplying the drug together with the polyamine whose synthesis was inhibited. The uptake and accumulation of exogenously supplied polyamines throughout the culture period was followed. The involvement of the three classes of polyamines in rhizogenic response is discussed in relation to the effect of the inhibitors of their biosynthesis
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
Hormonal treatments to mitigate salt-stress effects on two commercial hybrids of Sorghum bicolor (L.) Moench: a comparison between IAA and eBL exogenous application effects
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