MOVEMENT OF THE TUBE CELL IN THE LILY STYLE IN THE ABSENCE OF THE POLLEN GRAIN AND THE SPENT POLLEN-TUBE

Our model proposes that pollen tube growth is a form of cell movement where the tube tip can be considered analogous to a migrating cell whi ch leaves a trail of extracellular matrix (the spent pollen tube) behi nd. We demonstrate that the tube cell can convey the sperm cells to th e ovule and effect fertilization even in the absence of the pollen gra in and the spent pollen tube. Adhesion is an integral part of cell att achment and movement in animal systems. We show that in vivo-grown pol len tubes grow beneath the cuticle of the stylar transmitting tract ep idermis and directly adhere to one another and the outer wall of the e pidermal cells. A fibrous wall material is found to cover the tip of t he pollen tube cell wall and the surface of the transmitting tract cel ls where the two adhere. Fixation methods to preserve adhesive compoun ds were used. The pollen tubes grown in vivo, but not in vitro, show s tar-shaped clusters of F-actin microfilaments in the region back from the tip, as seen by rhodamine-phalloidin staining. These configuration s are similar to focal adhesions seen in moving animal cells.