Structural and immunocytochemical characterization of the Ginkgo biloba L. sperm motility apparatus |
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Authors: | K C Vaughn K S Renzaglia |
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Institution: | (1) Southern Weed Science Research Unit, USDA Agricultural Research Service, Stoneville, Mississippi;(2) Department of Plant Biology, Southern Illinois University, Carbondale, Illinois |
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Abstract: | Summary. Ginkgo biloba and the cycads are the only extant seed plants with motile sperm cells. However, there has been no immunocytochemical characterization
of these gametes to determine if they share characteristics with the flagellated sperm found in bryophytes and pteridophytes
or might give clues as to the relationships to nonflagellated sperm in all other seed plants. To determine characteristics
of proteins associated with the motility apparatus in these motile sperm, we probed thin sections of developing spermatogenous
cells of Ginkgo biloba with antibodies to acetylated and tyrosinated tubulin and monoclonal antibodies that recognize mammalian centrosomes and
centrin. The blepharoplast that occurs as a precursor to the motility apparatus consists of an amorphous core, pitted with
cavities containing microtubules and a surface studded with probasal bodies. The probasal bodies and microtubules within the
blepharoplast cavities are labeled with antibodies specific to acetylated tubulin. Positive but weak reactions of the blepharoplast
core occur with the centrosomereactive antibodies MPM-2 and C-9. Reactions to centrin antibodies are negative at this developmental
stage. From this pre-motility apparatus structure, an assemblage of about 1000 flagella and associated structures arises as
the precursor to the motility apparatus for the sperm. The flagellar apparatus consists of a three-layered multilayered structure
that subtends a layer of spline microtubules, a zone of amorphous material similar to that in the blepharoplast, and the flagellar
band. Centrin antibodies react strongly with the multilayered structure, the transition zone of the flagella, and fibrillar
material near the flagellar base at the surface of the amorphous material. Both the spline microtubules and all of the tubules
in the flagella react strongly with the antibodies to acetylated tubulin. These localizations are consistent with the localizations
of these components in pteridophyte and bryophyte spermatogenous cells, although the blepharoplast material surrounding and
connecting flagellar bases does not occur in the seedless (nonseed) land plants. These data indicate that despite the large
size of ginkgo gametes and the taxonomic separation between pteridophytes and Ginkgo biloba, similar proteins in gametes of both groups perform similar functions and are therefore homologous among these plants. Moreover,
the presence of acetylated tubulin in bands of microtubules may be a characteristic shared with more derived non-flagellated
sperm of other conifers and angiosperms.
Correspondence and reprints: Southern Weed Science Research Unit, USDA Agricultural Research Service, P.O. Box 350, Stoneville,
MS 38776, U.S.A. |
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Keywords: | : Centrin Acetylated tubulin Spermatogenous cell Land plant evolution |
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