Re-modelling of Mitochondrial Respiration in Arabidopsis during Drought

Drought can severely limit growth and productivity of plants. To limit water loss by transpiration, plant leaves respond by reducing stomatal aperture. This simultaneously impairs CO2 uptake and can reduce carbon assimilation. Sustained irradiance in the absence of sufficient CO2 risks over-reduction of the photosynthetic and metabolic redox systems with potentially detrimental effects for the cell. In that situation, chloroplasts need to safely dissipate reductant for which several different mechanisms inside and outside the chloroplast have evolved. Mitochondrial electron transport can act as such an electron sink by reducing oxygen to water. The required capacity and flexibility to dissipate reductant are thought to be provided by uncoupling the electron flux to oxygen from the phosphorylation of ADP to ATP. Yet, our understanding of the significance, regulation and integration of the different uncoupling strategies in plant mitochondria is still limited. To investigate how (un-)coupling impacts drought acclimation, I have manipulated mitochondrial uncoupling capacity by combining mutants of Uncoupling Protein (UCP) and Alternative Oxidase (AOX1a). Phenotyping revealed slightly decreased drought tolerance and reduced leaf rosette areas of plants restricted in uncoupling, but differences were minor compared to published mutant phenotypes. Previous reports indicated altered cellular energy physiology in response to drought-related stresses. I sought to refine our understanding of the changes at subcellular level by monitoring selected key parameters in response to drought and related stresses using fluorescent protein biosensors. Despite consistent increases of ATP levels and more oxidised NAD in response to drought, subsequent monitoring of uncoupling mutants did not reveal differences between genotypes under any of the conditions tested. Surprisingly, dithiothreitol (DTT), a widely used chemical to induce reductive ER stress, strongly impaired root growth of aox1a and ucp1 uncoupling mutants. A connection between thiol-based reductive stress and mitochondrial electron transport flexibility has not been reported before, and was further investigated in isolated mitochondria. Measurements of oxygen consumption revealed increased respiration in response to DTT. Multiwell-based fluorimetric assays to monitor the proton motive force, pH gradient and membrane potential, and substrate depletion rates demonstrated that small thiol molecules can feed electrons into the electron transport chain. Based on the in planta and in organello insights, a refined model is proposed in which the mitochondria act as flexible cellular safe-guards against stress-induced cellular over- reduction not only by photosynthesis, but also by thiol-mediated reductive stress that may affect protein folding in the ER. Considering the critical interplay between plant respiratory physiology and mitochondrial architecture in stress responses, the final section of this thesis investigates intramitochondrial pH compartmentation. The successful establishment of lines targeting the cpYFP pH biosensor to different mitochondrial compartments enabled in vivo measurements of pH gradients between plant mitochondrial subcompartments, suggesting a pH gradient of 0.4 units across the inner mitochondrial membrane.Trockenheit kann das Wachstum und die Produktivität von Pflanzen stark einschränken. Pflanzen können den Wasserverlust durch Transpiration über die Spaltöffnungen in den Blättern regulieren und somit minimieren. Dies wiederum beeinträchtigt die CO2-Aufnahme und -Assimilation. Anhaltende Sonnenlichtexposition in Abwesenheit von ausreichend CO2 birgt das Risiko einer Überreduktion der photosynthetischen und metabolischen Redoxsysteme mit potentiell schädlichen Auswirkungen auf die Zelle. In dieser Situation müssen Reduktionsäquivalente gezielt aus dem Chloroplasten abgeleitet werden, wofür verschiedene Mechanismen innerhalb und außerhalb des Chloroplasten bestehen. Der mitochondriale Elektronentransport kann durch die Reduktion von Sauerstoff zu Wasser als Akzeptor für überschüssige Reduktionsäquivalente dienen. Es wird angenommen, dass die erforderliche Kapazität und Flexibilität durch die Entkopplung des Elektronenflusses von der Phosphorylierung von ADP zu ATP bereitgestellt wird. Das Verständnis von der Bedeutung, Regulation und Integration der verschiedenen Entkopplungsstrategien in Pflanzenmitochondrien ist jedoch limitiert. Um die Auswirkungen der (Ent-) Kopplung auf die Akklimatisation der Pflanze an Trockenstress zu untersuchen, wurde die Entkopplungskapazität genetisch via Alternative Oxidase (AOX1a) und Uncoupling Protein (UCP) manipuliert. Die Phänotypisierung zeigte eine leicht verminderte Trockenstresstoleranz und verringerte Blattrosettenflächen bei Pflanzen mit eingeschränkter Entkopplung, wobei die Unterschiede im Vergleich zu veröffentlichten Phänotypen gering ausfielen. Frühere Berichte zeigten eine Veränderung der zellulären Energiephysiologie infolge von Trockenstress. Ich habe diese Veränderungen auf subzellulärer Ebene eingehender untersucht, indem ich ausgewählte Schlüsselparameter und deren Reaktion auf Trockenstress mithilfe fluoreszenter Proteinbiosensoren ausgelesen habe. Zwar bewirkte Trockenstress eine konstante Erhöhung der ATP-Konzentrationen und der Oxidationsraten von NAD im Wildtypen, die anschließenden parallelen Messungen mit den Entkopplungsmutanten zeigten unter den getesteten Bedingungen aber keine Unterschiede zwischen den Genotypen. Überraschenderweise schränkte Dithiothreitol (DTT), ein verbreitetes Reagenz zur Induktion von reduktivem ER-Stress, das Wurzelwachstum der Entkopplungsmutanten aox1a und ucp1 stark ein. Ein Zusammenhang zwischen Thiol-basiertem reduktivem Stress und der Flexibilität des mitochondrialen Elektronentransportes wurde bisher nicht beschrieben und daher im Rahmen dieser Arbeit in isolierten Mitochondrien weiter untersucht. Messungen des Sauerstoffverbrauchs wiesen auf eine erhöhte Atmung nach Zugabe von DTT hin. Multiwell-basierte Fluorimetrie zur Aufzeichnung des pH-Gradienten und des Membranpotentials, den beiden Komponenten der protonenmotorischen Kraft, sowie die Messungen der mitochondrialen Atmungsraten zeigten, dass kleine Thiolmoleküle Elektronen in die Elektronentransportkette einspeisen können. Basierend auf den in in planta und in in organello Erkenntnissen wird ein neues Modell vorgeschlagen, in welchem die Mitochondrien als flexible Sicherheitsventile gegen stressinduzierte zelluläre Überreduktion fungieren. Somit bewahren Mitochondrien die Redox-Homöostase und damit vermutlich die Integrität des Photosynthese-Apparates und der oxidativen Proteinfaltung im ER. Der letzte Abschnitt dieser Arbeit widmet sich der intramitochondrialen pH-Kompartimentierung, welche sich in Stresssituationen abhängig von der Atmungsphysiologie der Pflanzen und der mitochondrialen Architektur verändert. Die erfolgreiche Etablierung von Pflanzenlinien, die den cpYFP pH-Biosensor in unterschiedlichen mitochondrialen Kompartimenten exprimieren, ermöglichte in vivo Messungen von pH-Gradienten zwischen mitochondrialen Kompartimenten der Pflanzen und deutet auf einen pH-Gradienten von 0,4 Einheiten über die innere mitochondriale Membran hin

D3: an Immersive aided design deformation method

International audienceIn this paper, we introduce a new deformation method adapted to immersive design. The use of Virtual Reality (VR) in the design process implies a physical displacement of project actors and data between the virtual reality facilities and the design office. The decisions taken in the immersive environment are manually reflected on the Computed Aided Design (CAD) system. This increases the design time and breaks the continuity of data workflow. On this basis, there is a clear demand among the industry for tools adapted to immersive design. But few methods exist that encompass CAD problematic in VR. For this purpose, we propose a new method, called D3, for "Draw, Deform and Design", based on a 2 step manipulation paradigm, consisting with 1) area selection and 2) path drawing, and a final refining and fitting phase. Our method is discussed on the basis of a set of CAD deformation scenarios

Proposition d'une Taxonomie Fonctionnelle des Environnements de Réalité Augmentée

8 pagesL'objectif de cet article est double. Nous proposons premiè- rement une définition des environnements de réalité aug- mentée (RA). Ensuite nous proposons, basée sur notre dé- finition, une nouvelle taxonomie permettant de classer ces environnements. Après une brève revue des classifications existantes, nous définissons la RA par sa finalité qui est de permettre à une personne de réaliser des activités sensori- motrices et cognitives dans un nouvel espace en associant l'environnement réel et un environnement virtuel. Nous pré- sentons ensuite notre taxonomie fonctionnelle des environ- nements de RA. Nous divisons ces environnements en deux groupes distincts. Le premier concerne les différentes fonc- tionnalités permettant de s'informer et de comprendre notre environnement, une perception augmentée de la réalité. Le deuxième correspond aux applications ayant pour finalité de créer un environnement imaginaire. Enfin, plus qu'une dif- férence fonctionnelle, nous démontrons qu'il est possible de considérer que les deux types de RA ont une finalité prag- matique. La différence semble donc tenir à la capacité de ces deux types de RA à s'affranchir ou pas de la localisation spatio-temporelle

New Augmented Reality Taxonomy: Technologies and Features of Augmented Environment.

978-1-4614-0063-9This article has a dual aim: firstly to define augmented reality (AR) en- vironments and secondly, based on our definition, a new taxonomy enabling these environments to be classified. After briefly reviewing existing classifica- tions, we define AR by its purpose, ie. to enable someone to create sensory- motor and cognitive activities in a new space combining the real environment and a virtual environment. Below we present our functional taxonomy of AR environments. We divide these environments into two distinct groups. The first concerns the different functionalities enabling us to discover and understand our environment, an augmented perception of reality. The second corresponds to applications whose aim is to create an artificial environment. Finally, more than a functional difference, we demonstrate that it is possible to consider that both types of AR have a pragmatic purpose. The difference therefore seems to lie in the ability of both types of AR to free themselves or not of location in time and space

User-Defined Gestural Interaction: a Study on Gesture Memorization

8 pagesInternational audienceIn this paper we study the memorization of user created gestures for 3DUI. Wide public applications mostly use standardized gestures for interactions with simple contents. This work is motivated by two application cases for which a standardized approach is not possible and thus user specific or dedicated interfaces are needed. The first one is applications for people with limited sensory-motor abilities for whom generic interaction methods may not be adapted. The second one is creative arts applications, for which gesture freedom is part of the creative process. In this work, users are asked to create gestures for a set of tasks, in a specific phase, prior to using the system. We propose a user study to explore the question of gesture memorization. Gestures are recorded and recognized with a Hidden Markov Model. Results show that it seems difficult to recall more than two abstract gestures. Affordances strongly improve memorization whereas the use of colocalization has no significant effect

Vergence tracking: a tool to assess oculomotor performance in stereoscopic displays

Oculomotor conflict induced between the accommodative and vergence components in stereoscopic displays represents an unnatural viewing condition. There is now some evidence that stereoscopic viewing may induce discomfort and changes in oculomotor parameters. The present study sought to measure oculomotor performance during stereoscopic viewing. Using a 3D stereo setup and an eye-tracker, vergence responses were measured during 20-min exposure to a virtual visual target oscillating in depth, which participants had to track. The results showed a significant decline in the amplitude of the in-depth oscillatory vergence response over time. We propose that eye-tracking provides a useful tool to objectively assess the timevarying alterations of the vergence system when using stereoscopic displays

A Methodology to Assess the Acceptability of Human-Robot Collaboration Using Virtual Reality

International audienceRobots are becoming more and more present in our everyday life: they are already used for domestic tasks, for companionship activities, and soon they will be used to assist humans and collaborate with them in their work. Human-robot collaboration has already been studied in the industry, for ergonomics and efficiency purposes, but more from a safety than from an acceptability point of view. In this work, we focused on how people perceive robots in a collaboration task and we proposed to use virtual reality as a simulation environment to test different parameters, by making users collaborate with virtual robots. A simple use case was implemented to compare different robot appearances and different robot movements. Questionnaires and physiological measures were used to assess the acceptability level of each condition with a user study. The results showed that the perception of robot movements depended on robot appearance and that a more anthropomorphic robot, both in its appearance and movements, was not necessarily better accepted by the users in a collaboration task. Finally, this preliminary use case was also the opportunity to guarantee the relevance of using such a methodology -- based on virtual reality, questionnaires and physiological measures --for future studies

Un flou adaptatif en fonction du point de focalisation pour réduire la fatigue visuelle en vision stéréoscopique

National audienceDepuis quelques années, de plus en plus de contenus stéréoscopiques sont disponibles au grand public. Si l'impression de relief est remarquable, il n'en reste pas moins que la vision artificielle stéréoscopique demeure fatigante. Une cause de cette fatigue est le conflit accommodation convergence. Dans cet article, nous proposons d'ajouter un flou dans la vision périphérique (le point de focalisation étant déterminé avec un eye-tracking) pour limiter ce conflit et donc limiter la fatigue visuelle

Evaluation of a Vibrotactile Device For Outdoor and Public Transport Pedestrian Navigation Using Virtual Reality

International audienceIt can be difficult to find your way in public transport, especially when the journey combines indoor and outdoor trans-portation. We designed an innovative vibrotactile device dedicated to guide a pedestrian in public transport. This multi-modal interface can be used to guide a pedestrian in unknown public transport. The device can be used by visually impaired person. The device has been tested during two main phases. The first step was to test the device using virtual reality while the second step test was to test the device in a real environment. This paper presents the first part of the evaluation of the device. We have developed a virtual reality scenario to assess the objective and subjective utility of the device. The results showed that the device could properly guide users. We also evaluated the usefulness of a warning vibration preceding a message. It was found that the vibration seems to introduce confusion to the pattern recognition by the user

Business Process Management in Public Administrations – The PICTRUE Approach

Due to the changes in the structures of public administrations within the European Union, business process management has moved into the focus of public decision makers. Several projects with established modelling and reorganisation approaches from the private sector show (Fraser et al. 2003; Seltsikas and Palkovits 2006), that the specific legal, personnel, and political conditions rule out a careless adoption of these approaches for the public sector. Especially, the high amount of public services requires an efficient representation of the entire process landscape in order to measure the overall reorganisation potential. Focusing on isolated processes only leads to small local improvements (Raster 1994). In this paper the PICTURE-approach for an integrated business process management in public administrations is presented. The PICTURE-method allows for an efficient documentation of the entire process landscape in a public administration and a detailed analysis of the resulting process descriptions