Confocal imaging and immunogold electron microscopy of changes in distribution of myosin during pollen hydration, germination and pollen tube growth in Nicotiana tabacum L.

Using anti-myosin antibodies, standard immunocytochemical techniques in conjunction with confocal scanning laser microscopy and colloidal gold immunoelectron microscopy we compare changes in the distribution patterns of myosin during the early stages of pollen hydration, germination, tube growth, and myosin associated with isolated vegetative nucleus and the generative cell in Nicotiana tabacum L. Furthermore, on the Western blots of pollen tube proteins, the antimyosin antibodies crossreact only with one polypeptide of approximately 174 kDa. Confocal immunofluorescence microscopy reveals that in hydrated pollen, myosin is discretely associated with the cytoplasmic organelles and numerous punctate structures present in the center of the pollen. Within 30 min following transfer of pollen into the germination medium, that is, with the onset of germination, the centrally located punctate structures are displaced, and we find accumulation of myosin-associated organelles towards one of the germinal apertures from which the pollen tube would emerge. Subsequently, after 45 min of germination with the emergence of germination structure, few punctate structures are detected in the vegetative cytoplasm while intense immunostain is detected just below the plasma membrane of the emerging pollen tube tip. In the older parts of both short and long pollen tubes after 90 to 120 min of pollen germination, few fluorescent structures were found in the pollen tubes, however, numerous punctate fluorescent spots were concentrated in the tip region over a distance of 2 to 3 mu m below the plasma membrane of the tube tip. This is further substantiated by colloidal gold immunoelectron microscopy wherein clusters of gold particles are associated with vesicle-like structures in the tip region of the pollen tubes. The immunolocalization results presented here differ significantly from those previously published by revealing the presence of high level of immunostain that is restricted to 2 to 3 mu m adjacent to the tube tip. Myosin immunostain and immunogold label was present at discrete locations on the surface of the vegetative nucleus wherein the immunostain occurs as regularly placed clusters. Our results demonstrate that apart from being associated with the surface of the generative cells myosin is present inside the generative cells, on the nuclear envelope and in the nucleoplasm.