Modeling Cytoskeletal Dynamics and Vesicle Movements in Growing Pollen Tubes

Abstract

Intracellular cargo transport is a crucial process in growing plant cells. Since cellular expansion in walled cells entails the continuous assembly of new wall material, enormous amounts of polysaccharides need to be delivered to the growth site. In the rapidly elongating pollen tube the spatio-temporal movement pattern of exocytotic vesicles is precisely targeted and controlled by the continuously polymerizing actin cytoskeleton in the subapical region of the cell. Remarkably, the cone-shaped target region at the apical pole of the cylindrical cell does not contain much filamentous actin. We model the vesicular trafficking using as boundary conditions the expanding cell wall and the actin array forming the subapical actin fringe. Dynamic advancement of this actin fringe was obtained by imposing a steady shape and constant polymerization rate of the actin filaments. Letting vesicle flux into and out of the apical region be determined by the orientation of the actin microfilaments was sufficient to generate a flow that corresponds in magnitude and orientation to that observed experimentally. This model explains how the cytoplasmic streaming pattern in the apical region of the pollen tube can be generated without the presence of filamentous actin.View Large Image | View Hi-Res Image | Download PowerPoint Slide