Many signaling molecules and cellular events, including Ca2+, pH, phosphatidyl inositol, endocytosis, exocytosis, vesicle trafficking, plasma membrane fusion and actin filament reorganization, have been shown to be separately or synergistically involved in regulating the accurate polarized growth of the pollen tube. The pollen tube is a typical cell in the apex that exhibits rapid,Betamethasone Dipropionate polarized growth. During the polarized growth of pollen tubes, the components of the cell wall and plasma membrane must be delivered to the tip of the pollen tube by precise vesicle trafficking and then secreted to enable membrane fusion. Thus, highly ordered cytoplasmic streaming and membrane fusion are critical factors in polarized pollen tube growth. In addition, the actin cytoskeleton and Ca2+ are well known to have important influences on pollen tube growth, and a disorder in either leads to cessation of pollen tube growth. Ca2+ also plays a crucial role in determining the velocity of cytoplasmic streaming, membrane fusion and actin cytoskeleton Fenoprofen Calcium reorganization. Some recent studies have shown that the actin cytoskeleton in the pollen tube not only functions as a track for vesicle trafficking but also directs the distribution of vesicles. If this actin cytoskeleton was destroyed, vesicles would not be accurately transported to the specific locus of the membrane at the apex, causing the pollen tubes to stop growing. Furthermore, previous reports have indicated that the interaction between actin and the plasma membrane initiates membrane fusion. Consequently, the actin cytoskeleton and Ca2+ are indispensable for many membrane-related physiological activities and may synergistically regulate these activities. However, little is known about the underlying mechanisms that regulate pollen development and pollen tube growth via the coordinated regulation of the membrane, actin cytoskeleton and Ca2+ because the functional ‘‘linkers‘‘ between these factors remain unknown. The annexin family is a class of proteins that can bind to the membrane in a Ca2+-dependent manner. The members of this family share an evolutionarily conserved structure that can be found in a wide variety of eukaryotic cells. In mammalian cells, annexins have been shown to be involved in crucial cellular processes, such as vesicle trafficking, membrane organization, signal transduction, actin cytoskeletal dynamics and ion exchange.