CYTOPLASMIC MOTORS AND POLLEN-TUBE GROWTH

The growth of pollen tubes is characterized by an intense cytoplasmic streaming, during which the movements of smaller organelles (like secr etory vesicles) and larger ones (including the generative cell and veg etative nucleus) are precisely coordinated. A well-characterized cytos keletal apparatus is likely responsible for these intracellular moveme nts. In recent years both microfilament- and microtubule-based motor p roteins have been identified and assumed to be the translocators of th e several organelle categories. Their precise function during pollen t ube growth is not yet clear, but apparently an actomyosin-based system is mainly responsible for pollen tube elongation. On the other hand, microtubules and microtubule-based motors have been thought to play a role in the maintenance of cell polarity. Both cytoskeletal systems (a nd their respective motor activities) could cooperate to ensure a prec ise regulation of pollen tube growth.