Elongating at a rate of several micrometers per minute, pollen tubes are among the fastest growing cells known and are a good system for studying the development of cellular polarity. The pollen tube is believed to extend by a process of tip growth, in which secretory vesicles fuse with the growing tip of the tube to deliver cell membrane and cell wall material. The mechanism by which polarity is established in these cells has remained obscure, though a calcium gradient at the growing tip appears to have an important role (Pierson E.S., D.D. Miller, D.A. Callaham, J. van Aken, G. Hackett, P.K. Hepler. 1996. Dev. Biol. 174:160– 173). Work reported by Kost et al. (page ) provides the first direct evidence that a Rac-type small GTPase controls polar pollen tube growth by stimulating compartmentalized synthesis of phosphatidylinositol 4, 5-bisphosphate (PIP2).
After cloning At-Rac2, a Rac-like GTPase from...
