Cytoskeletal Basis of Organelle Trafficking in the Angiosperm Pollen Tube

Abstract The pollen tube is a cell with unusual features that plays a fundamental role during reproduction in higher plants, transporting the generative cell and sperm cells from the pollen grain to the ovary. Pollen tubes elongate by apical growth, which is, in turn, elicited by the fusion of secretory vesicles carrying plasma membrane and cell wall components. Organelle trafficking in the pollen tube, which occurs bi-directionally along the longitudinal axis, has been the focus of much research for many years. The movement of organelles along the pollen tube relies on the cytoskeleton, which consists of microtubules, actin filaments and associated proteins. Motor proteins are a special subset of cytoskeleton proteins that induce organelles to move by using the energy of ATP hydrolysis. The pollen tube, like other plant cells, uses actin-myosin interactions as a basis for the intracellular movement of organelles. The role of microtubules during organelle movement is not yet defined, despite the fact that microtubule motor proteins have been identified. The differential distribution of organelles and vesicles, which is observable along the main axis of the pollen tube, is essential for the proper growth of the pollen tube. How this level of organization is preserved is not known. However, other mechanisms of regulation are being identified in the pollen tube which might also be important in modulating the activity and structure of the cytoskeleton elements.