Diversity in meiotic spindle origin and determination of cytokinetic planes in sporogenesis of complex thalloid liverworts (Marchantiopsida) |
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Authors: | Roy C Brown Betty E Lemmon Masaki Shimamura |
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Institution: | (1) Department of Biology, University of Louisiana-Lafayette, Lafayette, LA 70504-2451, USA;(2) Department of Biological Science, Graduate School of Science, Hiroshima University, Kagamiyama Higashi-Hiroshima, 739-8526, Japan |
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Abstract: | As the earliest divergent land plants, bryophytes (mosses, hornworts, and liverworts) provide insight into the evolution of
the unique plant process of sporogenesis by which meiosis results in heavy walled spores. New immunohistochemical data on
microtubules and γ-tubulin in four genera of complex thalloid liverworts combined with previously published data on another
four genera demonstrate grades in the evolution of spindle organization in meiosis. We have discovered that all recognized
forms of microtubule organizing centers (MTOCs) in plant cells (plastid MTOCs, spheroid cytoplasmic MTOCs, polar organizers,
and nuclear envelope MTOCs) occur in organization of the meiotic spindle of complex thalloid liverworts. In addition, all
aspects of pre-meiotic preparation for quadripartitioning of the sporocyte into a tetrad of spores occur, with the exception
of pre-meiotic wall precursors found in certain simple thalloids. The preparation includes morphogenetic plastid migration,
cortical bands of microtubules that mark future cytokinetic planes in pre-meiosis, quadrilobing of the cytoplasm during meiotic
prophase, and quadripolar microtubule systems that are transformed into functionally bipolar metaphase I spindles. Quadripolar
spindle origin is typical of bryophyte sporogenesis even though the MTOCs involved may differ. However, in certain crown taxa
of complex thalloids the spindle develops with no traces of quadripolarity and placement of intersporal walls is determined
after meiosis, as is typical of higher plants. |
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Keywords: | |
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