Cover illustration: Time-lapse images of tobacco pollen tubes double-labelled with FM 1-43 (green) and FM 4-64 (red) to identify sites of endocytosis and exocytosis and to visualize membrane trafficking patterns. The first three images are from a pollen tube undergoing normal growth. The next three images are from a pollen tube undergoing hypertonic stress, which stimulates endocytic membrane retrieval at the apex and inhibits exocytosis. The last two images are from a pollen tube undergoing hypotonic stress, which stimulates exocytosis and growth and attenuates endocytosis. Together with previous work, these data reveal that transcellular hydrodynamic flux is a key integrator of pollen tube growth, providing a motive force for cell elongation and regulating the rates of membrane insertion (exocytosis) and retrieval (endocytosis). (See Zonia and Munnik, pp. 861-873.)
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