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SeMoVi - 040315 Douady Joyeux Mirabet

SeMoVi Seminar, 4th of march 2015

Location : Ecole Normale Superieure de Lyon (ENS Lyon), Blaise Pascal Conference Centre, LR6 building, room C 023, 46 allée d'Italie, Lyon. Map available here.

 

 

2.00 - 3.00

Stéphane Douady

laboratoire Matière et Systèmes Complexes, CNRS-Université Paris 7

Growth and Shape of Plants: how they are linked by movements

3.00 - 3.30 Coffee break  

3.30 - 4.00

Marc Joyeux

(Laboratoire de Spectrométrie Physique, CNRS-UJF Grenoble).

To buckle or not to buckle: Modeling of the fast movements of Dionaea, Aldrovanda, and Utricularia
4.00 - 4.30

Vincent Mirabet

CNRS-INRA-ENS de Lyon

 

Cell anisotropy and microtubules

4.30 - 5.00  General discussion  

 

 

 

Growth and Shape of Plants: how they are linked by movements

 

Stéphane Douady (laboratoire Matière et Systèmes Complexes, CNRS-Université Paris 7)

 

From the appearance of the primodium to the final shape of the mature organ, typically a leaf as Ghoete said, the expansion happens with many movements. As Hoffmeister first described, the growth of the primordium, initially a symmetric bump, is already an asymmetric growth, the surface increasing more than the base. The further development is also asymmetric, the length increasing more than the width increasing much more than the thickness that remains pretty constant. There is also the asymmetry between the part of the surface against the stem (adaxial) and away from it (abaxial). These asymmetric development gives rise to the shape, but also possibly to bending, hence many movements. We will describe some of these movements, and try to show how they are related to the final shape of the leaf (folding in the bud), or its final position in space (flat and horizontal, with the nutations).

 

To buckle or not to buckle: Modeling of the fast movements of Dionaea, Aldrovanda, and Utricularia

Marc Joyeux (Laboratoire de Spectrométrie Physique, CNRS-UJF Grenoble)

 

Buckling is characterized by a sudden failure of an object submitted to a stress smaller than the ultimate stress that the material is capable of withstanding. Buckling of their tissues is one of the mechanisms that plants have evolved to achieve velocities larger than those that may be reached by the sole regulation of the volume of antagonistic motor cells through the variation of their osmotic pressure. It is, however, not always possible to determine unambiguously what mechanism is at play in a particular plant from the examination of high-speed videos alone. For example, there still exists a controversy regarding the origin of the closing of the leaves of Dionaea in about 400 ms, although this plant has been intensively studied since Darwin's work. Moreover, the movement of other plants, like the aperture of the door of aquatic Utricularia's traps in about 1 ms, is just a little too fast for most of today's cameras. Modeling of these movements therefore represents an appealing complementary tool to unveil their complex dynamics.In this talk, I will report on the models we have recently developed to investigate the fast movements of Dionaea, Aldrovanda and Utricularia. The two key features of these models are the following: (i) they are based on realistic trap geometries obtained from triangulated surfaces; (ii) plant tissues are modeled as thin and homogeneous elastic solid membranes with a Young's modulus E close to 10 MPa, in agreement with experimental observations. These membranes are subjected to the adequate stress and the evolution equations for each vertex are solved numerically.I will show that these models reproduce accurately the movements of the investigated plants. More interestingly, a closer examination of the properties of the computed movements provides those details, which are not easily extracted from videos. For example, the models confirm that the closure of Dionaea's traps and the opening of the door of Utricularia's ones indeed involve the buckling of their tissues, while the snapping of the leaves of Aldrovanda in about 100 ms is more likely based on the kinematic amplification of the bending motion of their midrib.
 

 

 

Cell anisotropy and microtubules

Vincent Mirabet (Laboratoire de Reproduction et Développement des Plantes, CNRS-INRA-ENS de Lyon)

 

Morphogenesis in plants is mainly due to anisotropic growth of tissues, indeed plant cells are tightly bound together and very rarely migrate. Plant cells regulate their growth through controlled expansion of their rigid wall. Inside this rigid wall, cellulose microfibrills' orientation is anisotropic, and their direction guides the wall expansion. Inside the cell, the microtubule network is a major actor of cellulose orientation. As these proteic fibrills undergo constant reshuffling, it is crucial to understand how their configuration is maintained and regulated to understand cell wall anisotropy. For some years now, it has been shown that stress and cell deformations are factors modulating microtubule orientations. Nevertheless, little is known about the influence of shape on the microtubule orientation. It this study, I use a 3D model of cells and simulate virtual microtubules following standart interactions rules as defined in the literature. I show that cell shape can be of strong influence on the spontaneous properties of the microtubule network. Knowing those spontaneous configurations is crucial to be able to separate observations between normal configurations and altered ones.

 

 

You can find the poster here.

 

 

THIS SEMINAR IS SPONSORED BY :

 

 

 

 

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