Tubulin and Male-gamete Interconnections in the Pollen Tubes of the Grass Alopecurus pratensis

Abstract
Tubulin was localized in pollen tubes of the grass Alopecurus pratensis by immunofluorescence using a rat monoclonal yeast antitubulin as a primary antibody. In tubes fixed in active growth with paraformaldehyde fixative and permeabilized with detergent, the two male gametes were found to be linked by tubulin-containing cytoplasmic bridges. The connections appeared to persist throughout the growth of the tube, but they were highly mutable, the distance between the gamete pair varying greatly, the gametes sometimes actually overlapping in the tube. Systems of longitudinally disposed, discrete microtubule strands comparable with those seen in generative cells of species with bicellular pollen grains were not observed in the gametes. However, an envelope of antitubulin-binding material was apparent at the cell boundary in many instances, possibly to be interpreted as a sheath of closely packed microtubules seen in profile. Irregular masses, probably representing pools of unpolymerized or partly polymerized tubulin, were also present in most of the gametes.

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