The spatial display of stem and leaves is crucial for the functioning of plants and their mutual interactions. It involves complex movements : stem change curvature and orientation to rise vertically (gravitropism) and these movements is continously regulated by internal process (autotropism) (R. D. Firn [1979]). If a lot is known about the Physiology, very few studies have delt with the kinematics and dynamics of these movements, and the corresponding relevant physical and biological aspects (see Moulia and M. [2009] for a recent review). In this work we focused on the reaction of a wheat coleoptile using a novel high spatio-temporal kinematical method called "Beam PIV" combining Particlue Image Velocymetry (Supatto et al. [2005]) and contour and median line detection of the organ: When its orientation vs the gravity is modified by tilting the plant , this organ bends through local variation of curvature due to the differential growth, displaying a complex spatio-temporal pattern including oscillatory and propagative aspects. Both the elongative growth and differential growth displayed coupled propagative oscillation. The insights of these results in terms of the modelling of the biomechanical and regulatory processes will be discussed as well as the possible adaptive significance of this coupled osillators for the gravitropic performance.

References
B. Moulia and Fournier M. The power and control of gravitropic movements. Journal of Experimental Botany (Darwin series invited review), On press, 2009.

J. Digby R. D. Firn. A study of the autotropic straightening reaction of a shoot previously curved during geotropism. Plant, Cell and Environment, 2(2):149-154, 1979.

Willy Supatto, Delphine D'ebarre, Bruno Moulia, Eric Brouz'es, Jean-Louis Martin, Emmanuel Farge, and Emmanuel Beaurepaire. In vivo modulation of morphogenetic movements in Drosophila embryos with femtosecond laser pulses. Proceedings of the National Academy of Sciences of the United States of America, 102(4):1047-1052,
2005.