During plant fertilization, male genetic material moves from the pollen grain into the ovule along a pollen tube. This slender tube is formed by polarized tip growth, which involves targeting and fusion of secretory vesicles with the apical plasma membrane (PM). But the amount of vesicle fusion greatly exceeds the amount by which the PM is extended; so how is excess membrane retrieved? On p. 3804, Alessandra Moscatelli and colleagues report that several distinct endocytic pathways – including a clathrin-independent one – do this in tobacco pollen tubes. The authors use positively and negatively charged nanogold (which labels subapical and apical PM domains, respectively) and electron microscopy to show that the subapical PM is mostly recycled by the secretory pathway after internalization but the apical PM mostly follows a degradative pathway to vacuoles. The authors then use ikarugamycin (an inhibitor of clathrin-dependent endocytosis) to show that PM recycling and at least one degradative pathway involve clathrin-dependent endocytosis. Importantly, however, their experiments also demonstrate that, as in animal cells, clathrin-independent endocytosis occurs in plants.
- © The Company of Biologists Limited 2007