Figure 10.

Model for the Recycling of GTPase to the Pollen Tube Tip through GAPs, GDIs, and GEFs.

This model postulates that tip-localized GTPase flows with the newly inserted membrane toward the flanks of the pollen tube, where it gets inactivated by RhoGAP1. Localization of RhoGAP1 is dependent on helper proteins, such as 14-3-3, which are sensitive to lipid composition, pH, or ion gradients. At the flank of the tube, inactive, GDP-bound GTPase is then detached from the membrane by a GDI, which then transports it back to the apex, where it gets reactivated by a GEF. Interaction between components of the cell wall, the actin cytoskeleton, the membrane, and the cytoplasm may synergistically maintain this cycle on several planes of action.