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Cell Wall plasticity regulation in pollen tubes related to mechanical stress
No full textThe pollen tube is a rapidly growing plant cell that features particular traits that can only be understood when integrating cell biological with cell mechanical concepts. Firstly, regular temporal variations in the growth rate are governed by a feedback mechanism involving the regulation of the mechanical properties of the apical cell wall and mechanosensitive ion channels. Recent developments in image analysis have allowed making significant progress in the quantification of this behavior. Secondly, a pollen tube uses invasive growth to penetrate the flower tissues with the aim to transport the male sperm cells to their target, an ovule. Turgor was recently found to be the driving force of this invasive behavior and the mechanical underpinnings have been characterized using Lab-on-Chip (LOC) technology. Thirdly, the pollen tube is able to reorient its growth direction upon exposure to a guidance cue and the steering mechanism involves the sophisticated choreography of intracellular transport processes serving to fuel the polar growth process. This morphogenetic process relies on the precise spatial control of a gradient in the mechanical properties of the cell wall. Sophisticated imaging and micromanipulation techniques have been instrumental for the advancement in characterizing the biomechanical features of this crucial cell in the plant reproductive cycle. It has been recently shown that the pollen tube diameter changes in response to mechanical hindrance; this change in diameter suggests there is an adaptive mechanism within the cell wall formation pathway. In order to investigate this, pollen tubes from four plant species, Camellia sinensis, Nicotiana tabacum, Solanum chacoense and Arabidopsis thaliana, were germinated in media of varying stiffness to expose them to different degrees of mechanical stress during cell wall formation. Diameter has been correlated with the characteristic spatial profile of the distribution of cell wall polysaccharides. The pollen tubes were stained and immunolabeled to show beta-glycan contents as well as that of methyl esterified and de-esterified homogalacturonan (HG) to determine if the biochemical composition of the cell wall was affected by exposure to different types of mechanical environment. Though they grow in different pistil environments in vivo, both C. sinensis and A. thaliana had higher de-esterified HG content at the tip during growth in the stiff media suggesting the formation of a stiffer tip in response to stress. Some N. tabacum and S. chacoense pollen tubes displayed swollen bulbous tips with abnormal tip cell wall biochemistry suggesting this is an adaptive mechanism in response to stress. The abnormal swollen tips contained low levels of de- esterified HG in the bulbous tip cell wall suggesting this polysaccharide is necessary in maintaining pollen tube diameter during growth.Le tube pollinique est une cellule végétale dont la croissance rapide présente des caractéristiques particulières que l'on ne peut assimiler qu'en associant biologie cellulaire et concepts de mécanique cellulaire. Premièrement, les variations temporelles, à intervalles réguliers, du taux de croissance sont régies par un mécanisme de rétroaction associé à la régulation des propriétés mécaniques de la paroi cellulaire apicale et des canaux ioniques mécano- sensibles. Les récents développements en analyse d'images ont permis de faire d'importants progrès dans la quantification de ce mécanisme. Deuxièmement, la croissance invasive du tube pollinique lui permet de pénétrer les tissus du pistil afin de transporter les cellules spermatiques vers leur cible, un ovule. La force exercée par la turgescence est le principal moteur de ce comportement invasif dont les fondements mécaniques ont été caractérisés à l'aide de la technologie Lab-on-Chip (LOC). Troisièmement, le tube pollinique est capable de réorienter sa direction de croissance en réponse à un signal de guidage. Cette réorientation nécessite une régulation complexe des processus de transport intracellulaire contrôlant la croissance polaire. Ce processus morphogénétique repose sur le contrôle spatial précis d'un gradient de propriétés mécaniques de la paroi cellulaire. Les techniques de pointe en imagerie et en micromanipulation ont été déterminantes pour la caractérisation des propriétés biomécaniques de cette cellule, dont le rôle dans le cycle reproductif des plantes est crucial. Il a été récemment démontré que le diamètre du tube pollinique change en réponse à un obstacle mécanique. Ce changement de diamètre suggère l'existence d'un mécanisme adaptatif dans la formation de la paroi cellulaire. Afin de comprendre ce mécanisme, j'ai induit la germination de tubes polliniques de quatre espèces végétales, C. sinensis, N. tabacum, S. chacoense et A. thaliana, dans des milieux de différentes rigidités. Le but étant de les exposer à différents degrés de stress mécanique lors de la formation des parois cellulaires. Le diamètre des tubes a été comparé au profil de distribution spatial des beta-glycanes pariétaux. Les tubes polliniques ont été spécifiquement marqués par des anticorps afin de montrer la présence de beta-glycanes spécifiques ainsi que les pectines méthyl- estérifiées et dé-estérifiées. Le but de ces marquages est de déterminer si la composition biochimique de la paroi cellulaire serait affectée par les différentes propriétés mécaniques des milieux de croissance des tubes polliniques. Bien que les tubes polliniques de C. sinensis et d'A. thaliana germent in vivo dans différents environnements pistillaires, leurs apex sont caractérisés par une forte concentration en pectines de-estérifiées lorsqu'ils poussent, in vitro, dans des milieux rigides, suggérant ainsi la formation d'un apex plus rigide en réponse au stress. Certains tubes polliniques de N. tabacum et de S. chacoense sont caractérisés par des apex de forme bulbeuse et par une composition biochimie pariétale atypique au niveau apical, suggérant la présence d'un mécanisme adaptatif en réponse au stress. Les apex de forme atypique bulbeuse ont contenu des bas niveaux de pectines de-estérifiées dans la paroi cellulaire en soulignant que les pectines de-estérifiées sont nécessaires pour maintenir le diamètre du tube pollinique pendant la croissance
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
Probing cell behavior: Combining MEMS (microelectromechanical systems) technology with high resolution live cell imaging
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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
Microfluidic- and Microelectromechanical System (MEMS)-Based Platforms for Experimental Analysis of Pollen Tube Growth Behavior and Quantification of Cell Mechanical Properties
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