Cytoskeletal Elements, Cell Shaping and Movement in the Angiosperm Pollen Tube

The ellipsoidal generative cell of the pollen grain of Endymion nonscriptus usually elongates further following germination and entry into the tube, producing attenuated extensions the forward one of which may reach into the vicinity of the vegetative nucleus. This shape change is accompanied by the stretching of the microtubule cytoskeleton of the cell, identified in the present work by immunofluorescence using monoclonal antibodies to tubulin. Complementary observations of living generative cells of Iris pseudacorus showed that they undergo slow undulatory movements accompanied by variation in shape and length during passage through the tube. Such changes must presumably be accompanied by modifications of the microtubule cytoskeleton. Colchicine at 1 mM eliminated microtubules from tubes and most generative cells of E. nonscriptus, but did not radically affect pollen-tube shape or extension growth, nor arrest the movements of the vegetative nucleus and generative cell into and through the tube. Generative cells in colchicinetreated pollen of Galanthus nivalis rounded up and failed to undergo the usual changes in shape during passage through the tube. Secondary consequences were changes in precedence in movement through the tube, and a greater dispersal along its length. On the assumption that no other cytoskeletal elements remain to be discovered, it seems likely that microfilaments rather than microtubules provide the motive force for movement in the tube, although the latter are involved in shaping the generative cell and adapting it to its passage.