Anja Geitmann
Institut de recherche en biologie v'eg'etale, D'epartement de sciences biologiques, Universit'e de Montr'eal, Canada

Plant cell growth and morphogenesis are often accompanied by dramatic changes in cell shape. These require the concerted action of two mechanical processes: the deformation (stretching) of the existing cell wall and the localized secretion of cell wall precursors. The latter process adds cell wall material to prevent the thinning of the stretched wall resulting from the former. Furthermore, exocytosis affects local mechanical properties of the cell wall. The precise targeting of the secreted material is therefore pivotal in order to obtain a particular change in cell shape.
In tip growing cells such as pollen tubes and root hairs the surface expansion and secretion events are limited to an extremely small area at the very tip of the cell. This spatial confinement results in unidirectional growth pattern that is easily quantified and modeled. The high speed of the growth process and the simple, cylindrical geometry make these cells ideal model systems for quantitative studies of cell morphogenesis.
Our goal is to generate a mechanical model of the growth process in the rapidly growing pollen tube using finite element and numerical methods. In order to base this model on more than simple geometrical data, we attempt to incorporate quantitative information on cellular parameters such as the dynamics of the mechanical cell wall properties, the precise location and quantity of the delivered wall material, and the spatial control of this delivery process by the cytoskeleton. We use biomechanical measurements such as micro-indentation as well as high temporal resolution imaging in combination with spatio-temporal image correlation spectroscopy to quantify these cellular parameters