1,721,047 research outputs found
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
Fungal Endophytes Enhance the Photoprotective Mechanisms and Photochemical Efficiency in the Antarctic Colobanthus quitensis (Kunth) Bartl. Exposed to UV-B Radiation
Full text linkAntarctic plants have developed mechanisms to deal with one or more adverse factors which allow them to successfully survive such extreme environment. Certain effective mechanisms to face adverse stress factors can arise from the establishment of functional symbiosis with endophytic fungi. In this work, we explored the role of fungal endophytes on host plant performance under high level of UV-B radiation, a harmful factor known to damage structure and function of cell components. In order to unveil the underlying mechanisms, we characterized the expression of genes associated to UV-B photoreception, accumulation of key flavonoids, and physiological responses of Colobanthus quitensis plants with (E+) and without (E−) fungal endophytes, under contrasting levels of UV-B radiation. The deduced proteins of CqUVR8, CqHY5, and CqFLS share the characteristic domains and display high degrees of similarity with other corresponding proteins in plants. Endophyte symbiotic plants showed lower lipid peroxidation and higher photosynthesis efficiency under high UV-B radiation. In comparison with E−, E+ plants showed lower CqUVR8, CqHY5, and CqFLS transcript levels. The content of quercetin, a ROS-scavenger flavonoid, in leaves of E- plants exposed to high UV-B was almost 8-fold higher than that in E+ plants 48 h after treatment. Our results suggest that endophyte fungi minimize cell damage and boost physiological performance in the Antarctic plants increasing the tolerance to UV-B radiation. Fungal endophytes appear as fundamental biological partners for plants to cope with the highly damaging UV-B radiation of Antarctica.Fil: Barrera, Andrea. Universidad de Talca; ChileFil: Hereme, Rasme. Universidad de Talca; ChileFil: Ruiz Lara, Simon. Universidad de Talca; ChileFil: Larrondo, Luis. Pontificia Universidad Católica de Chile; ChileFil: Gundel, Pedro Emilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Pollmann, Stephan. Universidad Politécnica de Madrid; EspañaFil: Molina Montenegro, Marco A.. Universidad de Talca; ChileFil: Ramos, Patricio. Universidad de Talca; Chil
Caracterización del mecanismo integrador de señales de la respuesta de indol-3-acetamida y del desarrollo bajo condiciones de estrés abiótico en Arabidopsis thaliana
No full textAbiotic stresses greatly condition developmental processes in plants, and to decipher the growth-defense tradeoff phenomenon is key to understanding the fate of energy resources and their distribution to either defense or investment in development. Phytohormones are contributing to the regulation of this energy distribution and, among them, ABA is the phytohormone with the greatest influence on responses to abiotic stresses. On the other side, auxins are major growth factors in plants that drive virtually all aspects of plant growth. Hence, deeper insight into the crosstalk between auxins and ABA is fundamental to understanding the growth-defense tradeoff phenomenon. Auxin biosynthesis proceeds via a number of pathways. The indole-3-acetamide pathway is one of those routes. It is named according to its main intermediate, indole-3-acetamide, which is converted to indole-3-acetic acid by the virtue of AMIDASE1 (AMI1). In a microarray comparing ami1 null mutants with wild-type Arabidopsis, a significant proportion of the upregulated genes appeared to be associated with ABA responses. Amongst those genes, we found two myoblastosis protein (MYB) transcription factors, namely MYB74 and MYB102. In order to elucidate the molecular processes in which the two factors are involved, knock-out mutants of MYB74 and MYB102 were subjected to various analyses such as a drought, osmotic and salinity stress assays, phenotypic analyses of root architecture, as well as transcriptomics analyses and in silico analyses. Here, we roport the relation of MYB74 with drought resistance in Arabidopsis and its impact on the root system architecture. MYB102, in contrast, participates in seed development and in osmotic stress resistance in seedlings. In view of the fact that both factors do not entirely overlap in their functions although showing a large primary sequence identity, an in silico approach was taken in order to investigate the possible structural differences between MYB74 and MYB102, which could explain the functional differences of the two factors
The jasmonic acid signaling pathway is linked to auxin homeostasis through the modulation of YUCCA8 and YUCCA9 gene expression
No full textInteractions between phytohormones play important roles in the regulation of plant growth and development, but knowledge of the networks controlling hormonal relationships, such as between oxylipins and auxins, is just emerging. Here, we report the transcriptional regulation of two Arabidopsis YUCCA genes, YUC8 and YUC9, by oxylipins. Similar to previously characterized YUCCA family members, we show that both YUC8 and YUC9 are involved in auxin biosynthesis, as demonstrated by the increased auxin contents and auxin-dependent phenotypes displayed by gain-of-function mutants as well as the significantly decreased indole-3-acetic acid (IAA) levels in yuc8 and yuc8/9 knockout lines. Gene expression data obtained by qPCR analysis and microscopic examination of promoter-reporter lines reveal an oxylipin-mediated regulation of YUC9 expression that is dependent on the COI1 signal transduction pathway. In support of these findings, the roots of the analyzed yuc knockout mutants displayed a reduced response to methyl jasmonate (MeJA). The similar response of the yuc8 and yuc9 mutants to MeJA in cotyledons and hypocotyls suggests functional overlap of YUC8 and YUC9 in aerial tissues, while their function in roots shows some specificity, probably in part related to different spatio-temporal expression patterns of the two genes. These results provide evidence for an intimate functional relationship between oxylipin signaling and auxin homeostasis
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
In-depth analysis of jasmonate-mediated indole-3-acetic acid (IAA) biosynthesis and its implication in plant development
No full textEl ácido-3-indol-acético (AIA) es la auxina principal presente en las plantas. Esta hormona vegetal regula diversos procesos fisiológicos, siendo esencial para el correcto crecimiento y desarrollo de las plantas. Sin embargo, a pesar de que el estudio de esta auxina es uno de los campos de estudio más antiguos en biología vegetal, algunos aspectos de su biosíntesis, regulación espacio-temporal, mecanismos moleculares de acción, así como la interacción con otras hormonas, está aún por determinarse. En la actualidad, aunque se han descrito diversas rutas para la biosíntesis del AIA, el desarrollo de numerosos estudios bioquímicos y genéticos ha permitido determinar que la ruta del indol-3-piruvato (IPA) es la principal fuente de producción de AIA en plantas. La biosíntesis de AIA por la ruta metabólica del IPA comprende la acción consecutiva de dos clases de enzimas, las triptófano-piruvato aminotransferasas (TRIPTOFANO AMINOTRANSFERSA DE ARABIDOPSIS1 (TAA1)/TRIPTOFANO AMINOTRANSFERAS RELACIONADAS (TAR)) y las monooxigenasas dependientes de flavina (YUCCA). Entre estas familias, los genes YUCCA muestran una amplia distribución, siendo posible encontrarlos en diferentes genomas de plantas. Este hecho remarca el importante papel que dichos genes desempeñan, no sólo en lo relativo a la biosíntesis de la AIA, sino también en el desarrollo vegetal. Por otro lado, estudios recientes indican que la aplicación exógena de metil jasmonato (MeJA) o la producción endógena de ácido jasmónico (JA), una fitohormona implicada en la regulación de la respuesta de defensa frente a patógenos necrótrofos e insectos herbívoros, es suficiente para estimular la producción de AIA a través de la activación transcripcional de los genes YUCCA8 y YUCCA9. El trabajo descrito en esta tesis tiene como objetivo elucidar los mecanismos moleculares de acción de la auxina mediante la caracterización detallada de las líneas transgénicas de Arabidopsis 35S::YUCCA8 (YUC8ox) y 35S::YUCCA9 (YUC9ox), las cuales son sobreproductoras de AIA. Para lograr el objetivo planteado, se han realizado análisis histoquímicos, así como ensayos de cuantificación de la lignina. En concreto, se ha demostrado que un aumento exagerado de la producción de auxina da lugar a un crecimiento secundario anormal, en el cual se ha observado tanto una diferenciación del xilema y fibras interfasciculares, así como una lignificación, ambas altamente estimuladas. Igualmente, la caracterización de la composición de la lignina ha permitido determinar la alta deposición de unidades de lignina tipo H. Además, el desarrollo de microarrays comparando plantas Col-0 (silvestre) con las líneas transgénicas YUC8ox y YUC9ox, ha permitido revelar un incremento en la expresión en un grupo de genes implicados en la regulación de procesos asociados con la modificación de la pared celular de las plantas. Entre los genes encontrados, los conocidos como XILOGLUCANO ENDOTRANSGLICOSIDASA/ HIDROLASA (XTH) fueron particularmente relevantes. Así mismo, se ha corroborado que las plantas YUC8ox y YUC9ox presentan un incremento en los niveles de etileno (ET), una hormona gaseosa implicada en la regulación de la división celular. En conclusión, los datos presentados en este trabajo demuestran la importancia de la cascada hormonal JA-AIA-ET en el desarrollo de las plantas y desvelan un modelo de acción en el cual la activación de las enzimas YUCCA8 y YUCCA9 por JA estimula la producción de AIA, lo cual induce o inhibe la biosíntesis de etileno en determinados tejidos para regular la división celular en el cambium o la expansión celular en la epidermis. Además de esto, considerando la inactivación de la expresión en genes de respuesta a quitina y sequía, el presente estudio permite determinar que la interacción establecida entre JA y AIA actúa como mecanismo interruptor “encendido-apagado” en el balance entre crecimiento y defensa. Por otro lado, el trabajo de investigación aquí presentado ha estudiado los aspectos fisiológicos subyacentes al crecimiento secundario estimulado por la acción conjunta de IAA-ET. Se ha observado que tanto YUCCA8 como YUCCA9 confieren resistencia frente al ácaro herbívoro Tetranychus urticae, igualmente se ha visto que las plantas YUC9ox presentan mayor tolerancia a estrés por sequía, de esta manera estos resultados demuestran el papel esencial que desempeña la triple interacción JA-AIA-ET en la respuesta de las plantas a estrés. Finalmente, el mecanismo molecular por el cual interaccionan estas dos hormonas aparentemente antagonistas, ácido jasmónico y auxina, ha sido también dilucidado durante la realización de este estudio. Con este fin, se han analizado diferentes mutantes defectivos en varios factores de transcripción dependientes de jasmonato. Mediante ensayos de expresión transitoria en Nicotiana benthamiana y en protoplastos de Arabidopsis, se han confirmado que el factor de transcripción MYC2, así como sus dos homólogos más cercanos MYC3 y MYC4, actúan como reguladores transcripcionales de YUCCA8 y YUCCA9 a través de su unión directa a diferentes cajas G, localizadas en el promotor de los genes YUCCA mencionados. La presente tesis doctoral aporta por primera vez una prueba molecular que une la señalización del ácido jasmónico con la biosíntesis de auxinas. ABSTRACT Indole-3-acetic acid (IAA), the main naturally occurring auxin in plants, is an essential plant hormone that has been associated with the regulation of many aspects of plant development and growth. However, despite auxin biology is one of the classical fields of plant research, its biosynthesis, spatio-temporal regulation, molecular action and the crosstalk with other hormones remain uncertain. Actually, although multiple pathways are proposed for auxin biosynthesis, many previous genetic and biochemical studies revealed that the indole-3-pyruvic acid (IPA) pathway is the main source of IAA in plants. This pathway involves the action of two classes of enzymes, tryptophan-pyruvate aminotransferases (TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS 1 (TAA1)/TRYPTOPHAN AMINOTRANSFERASE RELATED (TAR)) and flavin monooxygenases (YUCCA). Among these families, the presence of the YUCCA genes in multiple plant genomes point out and essential role in biosynthesis and plant development. Current evidences indicate that exogenous application of methyl jasmonate (MeJA) or endogenous production of jasmonic acid (JA), a hormone with a prevalent role in plant defense to necrotrophic pathogens and insect herbivores, is sufficient to trigger IAA biosynthesis through the up-regulation of YUCCA8 and YUCCA9. The work described in this thesis aims at the elucidation of the molecular auxin action by in-depth analysis of 35S::YUCCA8 (YUC8ox) and 35::YUCCA9 (YUC9ox) Arabidopsis transgenic lines, which overproduce IAA. To this end we carried out histochemical analyses and quantitative lignification assays. These analyses allow us to finally determine that the overproduction of auxin cause an abnormal secondary growth, mainly characterized by a stimulated xylem and interfascicular fibers differentiation, as well as increased lignification, which is enriched in H-lignin deposition. Moreover, whole-genome transcriptomic analysis comparing YUC8ox and YUC9ox to wild-type Col-0 plants, revealed a cluster of up-regulated genes capable of modifying cell wall properties. Among those a group of XYLOGLUCAN ENDOTRANSGLYCOSYLASE/HYDROLASE (XTH) genes peaked out. Furthermore, when we analyzed the chemotype of the overexpression lines, we discovered significantly increased levels of ethylene (ET), a gaseous plant hormone with a prominent role in cell division. In conclusion, the results presented here highlight the importance of the hormonal cascade JA-IAA-ET in plant development. We propose a mechanistic model in which the activation of IAA production mediated by JA-induced YUCCA8 and YUCCA9 enzymes, stimulate or inactivate the production of ET to regulate vascular cell division or epidermal cell expansion in a tissue-specific manner. In addition, considering the observed down-regulation of different chitin and water deficit responses genes in the studied YUC8/9ox lines, we determine that the JA-IAA crosstalk is an on-off “switch” mechanism to fine-tune the balance between growth and defense processes. The physiological aspects underlying the IAA-ET induced secondary growth and cell expansion have been also unveiled in this thesis. Our results show that YUCCA8 and YUCCA9 mediate a positive defense response against the herbivore Tetranychus urticae, as well as, an improved drought tolerance for YUC9ox, thereby underlining a role of JA-IAA-ET in plant response. Finally, this thesis strives to shed light on the molecular relationship that share these two seemingly antagonistic hormones, jasmonic acid and auxin. Herein, we analyzed different mutants defective in known jasmonate-induced transcriptional factors. Our transient expression analysis in Nicotiana benthamiana and Arabidopsis protoplasts clearly demonstrate that MYC2, as well as its closest homologs MYC3 and MYC4, function as a transcriptional regulators of YUCCA8 and YUCCA9 through its direct binding to different G-boxes located at the promoter of the mentioned YUCCA genes. This study provides for the first time a molecular proof that links jasmonic acid signaling with auxin biosynthesis
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