A Mechanical Model to Interpret Cell-Scale Indentation Experiments on Plant Tissues in Terms of Cell Wall Elasticity and Turgor Pressure

International audienceMorphogenesis in plants is directly linked to the mechanical elements of growing tissues, namely cell wall and inner cell pressure. Studies of these structural elements are now often performed using indentation methods such as atomic force microscopy. In these methods, a probe applies a force to the tissue surface at a subcellular scale and its displacement is monitored, yielding force-displacement curves that reflect tissue mechanics. However, the interpretation of these curves is challenging as they may depend not only on the cell probed, but also on neighboring cells, or even on the whole tissue. Here, we build a realistic three-dimensional model of the indentation of a flower bud using SOFA (Simulation Open Framework Architecture), in order to provide a framework for the analysis of force-displacement curves obtained experimentally. We find that the shape of indentation curves mostly depends on the ratio between cell pressure and wall modulus. Hysteresis in force-displacement curves can be accounted for by a viscoelastic behavior of the cell wall. We consider differences in elastic modulus between cell layers and we show that, according to the location of indentation and to the size of the probe, force-displacement curves are sensitive with different weights to the mechanical components of the two most external cell layers. Our results confirm most of the interpretations of previous experiments and provide a guide to future experimental work

Multifarious Hierarchies of Mechanical Models for Artist Assigned Levels-of-Detail

International audienceWe present a new framework for artist driven level of detail in solid simulations. Simulated objects are simultaneously embedded in several, separately designed deformation models with their own independent degrees of freedom. The models are ordered to apply their deformations hierarchically, and we enforce the uniqueness of the dynamics solutions using a novel kinetic filtering operator designed to ensure that each child only adds detail motion to its parent without introducing redundancies. This new approach allows artists to easily add fine-scale details without introducing unnecessary degrees-of-freedom to the simulation or resorting to complex geometric operations like anisotropic volume meshing. We illustrate the utility of our approach with several detail enriched simulation examples

Sphingomyelin synthase-related protein SMSr controls ceramide homeostasis in the ER

Ceramides are central intermediates of sphingolipid metabolism with critical functions in cell organization and survival. They are synthesized on the cytosolic surface of the endoplasmic reticulum (ER) and transported by ceramide transfer protein to the Golgi for conversion to sphingomyelin (SM) by SM synthase SMS1. In this study, we report the identification of an SMS1-related (SMSr) enzyme, which catalyses the synthesis of the SM analogue ceramide phosphoethanolamine (CPE) in the ER lumen. Strikingly, SMSr produces only trace amounts of CPE, i.e., 300-fold less than SMS1-derived SM. Nevertheless, blocking its catalytic activity causes a substantial rise in ER ceramide levels and a structural collapse of the early secretory pathway. We find that the latter phenotype is not caused by depletion of CPE but rather a consequence of ceramide accumulation in the ER. Our results establish SMSr as a key regulator of ceramide homeostasis that seems to operate as a sensor rather than a converter of ceramides in the ER

Categorización del gusto en el arte del exilio a través de Max Aub, su conexión con Malraux, Jean Cassou y la bibliografía artística de los años cincuenta

With the passing of time, the novel published by Max Aub in Mexico 1958, Jusep Torres Campalans, uncovers itshelf as a mirror where we see the relationship between spanish and french historiography at the time, pertaining the spanish label, the vanguardias and Picasso, Goya and Juan Gris. A valuable addition to studies on the concept of spanish art, and spacifically spanish republican art in exile.Con el paso del tiempo, la novela que Max Aub publicó en México en 1958, Jusep Torres Campalans, se desvela como un espejo en el que vemos la relación de la historiografía española y francesa del momento con respecto a lo español, las vanguardias y Picasso, Goya, Velázquez y Juan Gris. Una aportación valiosa a los estudios sobre el concepto de arte español, especialmente el arte español republicano en el exilio

Gilberto Bosques and the flight of Spanish Republicans through Portugal, 1946-1949

Resumen: Partiendo de la polémica existente en torno a la valoración de la figura de Gilberto Bosques, en este artículo tratamos de realizar una nueva mirada, basada en una investigación con fuentes primarias inéditas, acerca de un período prácticamente desconocido de su participación en el salvamento de refugiados. Entre 1946 y 1949 Gilberto Bosques ejerció como embajador de México en Portugal, donde su principal labor volvió a ser la atención a los republicanos españoles que trataban de huir del franquismo. El nuevo contexto en el que tuvo que desenvolver sus funciones, a pesar del fin de la guerra, fue si cabe tan complejo como el anterior. Analizaremos los planes para el salvamento de españoles diseñados por Bosques, las dificultades en su implantación y sus resultados prácticos, sin dejar de lado la situación de estos exiliados, de los que trataremos de trazar un perfil social.Abstract: Onthe basis of the existing controversy surrounding the assessment of the Gilberto Bosques? figure, in this article we try to make a new view, based on research with unpublished primary sources, about a virtually unknown period of its participation in the rescue of refugees. Between 1946 and 1949 Gilberto Bosques served as Mexico?s ambassador in Portugal, where his main task was again the attention to the Spanish Republicans who tried to flee the Francoism. The new context in which they had to develop their functions, despite the end of the war, was as complex as the previous. We analyze the plans for the rescue of Spanish republicans designed by Bosques, the difficulties in its implementation and practical results. Finally westudy the situation of these exiles and we try to draw their social profile

Biosynthese de sphingomyelines a choline et a ethanolamine dans les microsomes et membranes plasmiques du foie et du cerveau de rat : localisation de l'enzyme microsomal

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Tourisme de qualité, diversification touristique et trajectoires territoriales du sud Ardèche . Mise en place d’indicateurs IQUATEXT appliqués au grand projet grotte Chauvet-Pont-d’Arc

The objective of this work is to question the processes and modalities of tourism quality, as well as the place of cultural tourism in the quality improvement of a tourist destination. It is a question of observing the existing interactions between sustainable development, quality and cultural tourism while specifying to what extent these concepts feed each other. This leads us to question the place of the diversification of the offer in the sustainability of the tourist destination. In the particular context of the evolution of the tourist offer following the discovery of a new heritage resource, this research aims to question the territorial implications of the diversification and quality of tourism. In order to respond to this problem, this doctoral research focused on the study of tourism in the southern Ardèche, where the discovery of the Chauvet-Pont-d'Arc cave led actors to rethink their tourism offer and the functioning of their territory. Based on the projects to enhance the value of this decorated cave (creation of a facsimile and inclusion of the cave on the UNESCO World Heritage List), the actors in the region have conducted a global reflection in order to develop their tourist offer towards quality cultural tourism. In a tourism context perceived by these same actors as limited from a sustainable development point of view and as a source of dysfunction (over-visitation, spatio-temporal concentration, etc.), this discovery was seized upon as an opportunity to shift the tourism system towards a quality heritage offer, perceived as having less impact and as being more favourable to the sustainable socio-economic development of the area. In addition to analysing contemporary processes and strategies aimed at the quality and diversification of the tourist offer, this doctoral research led to questioning the means that could be put in place to evaluate the impact of this territorial project. The realisation of a state of the art on the existing ac-tual means to evaluate the quality of tourism led to the implementation of a new evaluation and monitoring method: the IQUATEXT method (Indicators of Quality of Tourism and Territorial Excellence).L’objectif de ce travail est de questionner les processus et les modalités de la qualité du tourisme , ainsi que la place du tourisme culturel dans la montée en qualité d’une destination touristique. Il s’agit d’observer les interactions existantes entre le développement durable, la qualité et le tourisme culturel tout en précisant dans quelle mesure ces concepts se nourrissent les uns les autres. Ceci amène ainsi à interroger la place de la diversification de l’offre dans la durabilité de la destination touristique. Dans le contexte particulier de l’évolution de l’offre touristique suite à découverte d’une nouvelle ressource patrimoniale, cette recherche vise à questionner les implications territoriales de la diversification et de la qualité du tourisme.Afin de répondre à cette problématique, cette recherche doctorale s’est portée sur l’étude du tourisme sud ardéchois où la découverte de la grotte Chauvet-Pont-d’Arc a conduit les acteurs à repenser leur offre touristique et le fonctionnement de leur territoire. A partir des projets de valorisation de cette cavité ornée (réalisation d’un fac-similé et inscription de la grotte sur la liste du patrimoine mondial de l’UNESCO), les acteurs du territoire ont mené une réflexion globale afin de faire évoluer leur offre touristique vers un tourisme culturel de qualité. S’inscrivant dans un contexte touristique perçu par ces mêmes acteurs comme limité d’un point de vue du développement du-rable et comme porteur de dysfonctionnements (surfréquentation, concentration spatio-temporelle…), cette décou-verte a été saisie comme une aubaine pour infléchir le système touristique vers une offre patrimoniale de qualité, per-çue comme moins impactante et comme plus favorable pour développement socio-économique durable du territoire. Outre l’analyse des processus et des stratégies contemporaines visant la qualité et la diversifica-tion de l’offre touristique, cette recherche doctorale a conduit à interroger les moyens pouvant être mis en place pour évaluer les incidences de ce projet de territoire. La réalisation d’un état de l’art sur les moyens ac-tuels existants pour évaluer la qualité du tourisme a conduit à mettre en place une nouvelle méthode d’évalua-tion et de suivi : la méthode IQUATEXT (Indicateurs de QUalité du Tourisme et d’EXcellence Territoriale)

A mechanical model to interpret cell-scale indentation experiments on plant tissues in terms of cell wall elasticity and turgor pressure

Morphogenesis in plants is directly linked to the mechanical elements of growing tissues, namely cell wall and inner cell pressure. Studies of these structural elements are now often performed using indentation methods such as atomic force microscopy. In these methods, a probe applies a force to the tissue surface at a subcellular scale and its displacement is monitored, yielding force-displacement curves that reflect tissue mechanics. However, the interpretation of these curves is challenging as they may depend on not only the cell probed, but also on neighboring cells, or even on the whole tissue. Here, we build a realistic three-dimensional model of the indentation of a flower bud using SOFA (Simulation Open Framework Architecture), in order to provide a framework for the analysis of force-displacement curves obtained experimentally. We find that the shape of indentation curves mostly depend on the ratio between cell pressure and wall modulus. Hysteresis in force-displacement curves can be accounted for by a viscoelastic behavior of the cell wall. We consider differences in elastic modulus between cell layers and we show that, according to the location of indentation and to the size of the probe, force-displacement curves are sensitive with different weights to the mechanical components of the two most external cell layers. Our results confirm most of the interpretations of previous experiments and provide a guide to future experimental work