STRUCTURAL AND IMMUNOCYTOCHEMICAL CHARACTERIZATION OF MICROTUBULE-ORGANIZING CENTERS IN PTERIDOPHYTE SPERMATOGENOUS CELLS

During the development of the spermatogenous cells, the pteridophyte C eratopteris richardii produces three structurally well-defined microtu bule organizing centers (MTOCs). The blepharoplast, a spherical body t hat occurs during the last two spermatogenous divisions, organizes two microtubule (MT) arrays, one associated with a nuclear indentation an d the other that organizes the spindle apparatus for the final divisio ns. After the last spermatogenous division, the blepharoplast reorgani zes to produce two new putative MTOCs: the lamellar strip (LS) of the multilayered structure (MLS), which apparently organizes the spline mi crotubule array, and an amorphous zone (AM), that connects the basal b odies. Thin and semi-thin sections of this tissue were probed with ant isera which recognize MTOCs in lower eukaryotes and animals to determi ne if any of these structures contain MTOC-associated proteins or epit opes recognized by monoclonal antisera. Gamma tubulin antibodies, whic h recognize only the minus ends of MTs in mammalian cells, label along the MT in all arrays found in the pteridophyte sper spermatogenous ce lls. Kinetochore MTs are unlabelled near the kinetochore, however. The monoclonal antibodies MPM-2 and C-9, that recognize centrosomal and n uclear epitopes in mammalian cells, label the interphase nucleus, the cytoplasm of mitotic cells, and the blepharoplast during both nuclear indentation and spindle formation. Double labelling of the blepharopla st-containing cells with anti-tubulin and either MPM-2 or C-9 reveals that the blepharoprast-associated fluorescence is the focus of the tub ulin arrays. Centrin labels the reorganizing blepharoplast, the MLS, t he AM, and a stellate pattern in the transition region of the flagella . These data indicate the usefulness of the structurally well-recogniz ed MTOCs in pteridophyte spermatogenous cells in investigation of land plant MTOCs.