Generating a Cellular Protuberance: Mechanics of Tip Growth

Abstract

A plant cell grows by expansive deformation of its surface, the cell wall. Global cellular elongation growth and the mechanical principles governing this process are intensively studied, but the generation of cellular protuberances, a fundamental process required for the formation of complex plant cell geometries, remains poorly understood. Pollen, the male gametophyte stage of the flowering plants, is an excellent model system for the investigation of the mechanics of protuberance formation. The initiation of pollen tube growth requires the spatially confined formation of a bulge, followed by the elongation of the forming tube through tip growth. Since turgor is a nonvectorial force, this process must be controlled by the mechanical properties of the cell wall. In the elongating tube, cell wall expansion is confined to the apex of the cell, requiring the tubular region to be stabilized against turgor-induced tensile stress. How this is achieved, and why the pollen tube is so successful in invading other tissues, is elucidated from the point of view of cell mechanics.