Histopathology of the interaction between Ascochyta fabae and Vicia faba: comparison of susceptible and resistant reactions

Leaves of Vicia faba plants naturally or artificially infected with Ascochyta fabae were examined using light, scanning and transmission electron microscopy. Histological comparison was made of 1 resistant (29H) line and 1 susceptible (48B) line to study possible differences in symptom expression, host-cell necrosis and extent of fungal development. In the susceptible line, 48B, a lesion consisted of a central necrotic region where the fungus invaded intercellular spaces between the epidermis and the mesophyll. Although no fungal hyphae were found in the surrounding region, many cells had collapsed. In the resistant line, 29H, the fungus failed to develop during penetration. The host cells underlying fungal spores became orange-brown and a hypersensitive reaction caused flecking lesions. In addition, the granal lamellae of chloroplasts of the adjacent mesophyll cells were swollen and electron translucent. Necrotic lesions appeared in a few cases but remained limited. At the periphery of this lesion, many electron-dense bodies were attached to the walls of mesophyll cells.Histopathologie de l'interaction entre Ascochyta fabae et Vicia faba. Comparaison des réactions de sensibilité et de résistance. Des feuilles de féverole (Vicia faba L) prélevées sur des plantes naturellement et artifiellement infectées par Ascochyta fabae sont examinées en microscopie photonique et électronique à balayage et à transmission. Une lignée résistante (29H) est comparée d'un point de vue histologique à une lignée sensible (48B) afin de mettre en évidence d'éventuelles différences dans la symptomalogie, dans la colonisation des tissus par le parasite et dans les altérations produites sur les cellules hôtes. Chez la lignée sensible 48B, les lésions présentent une zone centrale nécrosée où le champignon envahit les espaces intercellulaires compris entre l'épiderme et le mésophylle. À la périphérie, beaucoup de cellules sont mortes sans colonisation des tissus par les hyphes du champignon. Chez la lignée résistante, le développement du parasite semble interrompu lors de la pénétration. Les cellules épidermiques en contact avec les spores du champignon brunissent et sont à l'origine d'une réaction hypersensible se traduisant par des «points rouille». De plus, les lamelles des thylakoïdes des chloroplastes situés dans les cellules adjacentes sont épaissies et transparentes aux électrons. Dans quelques cas, de véritables nécroses apparaissent, mais celles-ci restent limitées. À la périphérie de ce type de symptôme, les parois des cellules du mésophylle présentent de nombreux corpuscules denses aux électrons

Simplex based animation

We propose a methodology for animating complex models based on simplex mesh representation and deformation. A simplex mesh is characterized by a connectivity between vertices of three and can be obtained by duality from a triangulation. In addition to their generalityof representation, simplex meshes have a compact and unambiguous shape description, related to the notion of mean curvature. We devised a physically-based metamorphism algorithm that rests on the intrinsic shape representation of these meshes. This algorithm handles transformations between objects of di erent topology or boundary conditions. Various simplex mesh shapes were extracted from range images or some triangulated data and then metamorphosed by applying generalized mesh transformations

Dynamic Animation of Deformable Bodies

PublishedInternational audienceno abstrac

Cloth Animation with Self-Collision Detection

This paper addresses the problem of detecting collisions of very flexible objects, such as clothes with almost rigid bodies, such as human bodies. In our method, collision avoidance consists of creating a very thin force field around the obstacle surface to avoid collisions. This force field acts like a shield rejecting the points. This volume is divided into small contiguous non-overlapped cells which completely surround the surface. As soon as a point enters into a cell, a repulsive force is applied. The direction and the magnitude of this force are dependent on the velocities, the normals and the distance between the point and the surface. Particular cases are discussed with the ways of solving them

Animation Control with Dynamics

This paper discusses the advantages and disavantages of kinematics and dynamics in motion control for animating three-dimensional characters. It presents a motion control system based on dynamics. Applications of such a system are especially in the area of walking and grasping. It is shown that a simulation of writing a letter is a typical dynamic process. For the animation of the hand itself, a kinematic approach seems to be more convenient. The problem of surface deformations is also briefly mentioned Keywords: kinematics, dynamics, three-dimensional character, walking, writing, graspin

The Elastic Surface Layer Model for Animated Character Construction

A model is described for creating three-dimensional animated characters. In this new type of layered construction technique, called the elastic surface layer model, a simulated elastically deformable skin surface is wrapped around a traditional kinematic articulated figure. Unlike previous layered models, the skin is free to slide along the underlying surface layers constrained by reaction forces which push the surface out and spring forces which pull the surface in to the underlying layers. By tuning the parameters of the physically-based model, a variety of surface shapes and behaviors can be obtained such as more realistic-looking skin deformation at the joints, skin sliding over muscles, and dynamic effects such as squash-and-stretch and followthrough. Since the elastic model derives all of its input forces from the underlying articulated figure, the animator may specify all of the physical properties of the character once, during the initial character design process, after which a complete animation sequence can be created using a traditional skeleton animation technique. A reasonably complex character at low surface resolution can be simulated at interactive speeds so than an animator can both design the character and animate it in a completely interactive, direct-manipulation environment. Once a motion sequence has been specified, the entire simulation can be recalculated at a higher surface resolution for better visual results. An implementation on a Silicon Graphics Iris workstation is described