Polarized secretion is an essential process during the differentiation of different cell types and tissues in multicellular organisms. In plants, cells are surrounded by a rigid cell wall, which restricts changes in cell shape and size; therefore polarized secretion of cell wall components takes on a particular importance during plant growth and development. In recent years, significant advances have been made in discovering and characterizing proteins required for specific membrane trafficking steps along the secretory pathways of yeast, plants and animals. However, despite these advances little is known of the membrane trafficking pathways responsible for polarized secretion in plants.