Developmental and Structural Section
Arias, Tatiana , Williams, Joseph H. .
Embryology of Manekia naranjoana (Piperaceae) and the origin of tetrasporic, sixteen-nucleate female gametophytes in Piperales.
Piperaceae offers a unique opportunity to examine the evolution of endosperm genetic constitution, because it is exceptionally diverse in the underlying female gametophyte ontogenetic patterns that produce variation in endosperms. Within Piperaceae, Manekia is still unstudied and we report here that its female gametophyte is tetrasporic and sixteen-nucleate. However, there was considerable ontogenetic variation after polarization of the four-nucleate coenocyte, which fell into two classes: 1) bipolar or weakly bipolar organization and binucleate central cells at maturity (ca. 80 % of specimens); or 2) distinctly tetrapolar organization and tetranucleate central cells (ca. 20 % of specimens). These ontogenies and mature structures correspond to the Drusa type and Penaea type patterns, respectively. Penaea type has not been reported in Piperaceae to date. Heterochrony, heterotopy, novelties and sequence deletions have all played roles in modulating variation within Piperales. Based on comparative analysis of development, and consistent with current phylogenies, the common ancestor of Piperaceae was tetrasporic with a bipolar body plan (a plesiomorphic trait inherited from a monosporic, bipolar Polygonum type ancestor) and produced a “functionally bisporic” form of triploid endosperm derived from two megaspore descendants and a sperm. Subsequent modification of this ancestral ontogeny can account for the origin of all three other known “true” tetrasporic endosperm genetic constructs, which are formed from derivatives of all four megaspores and a sperm. These derived endosperms have higher ploidy, higher potential heterozygosity and a more stable transmission pattern, consistent with theoretical predictions.
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1 - The University of Tennessee, Ecology and Evolutionary Biology, 1406 Circle drive/319 Hesler building, Knoxville, TN, 37996, USA
2 - University of Tennessee, Department of Ecology and Evolutionary Biology, 442 Hesler Biology, Knoxville, Tennesee, 37996, USA
Female gametophyte development
Presentation Type: Oral Paper:Papers for Sections
Location: Boulevard C/Hilton
Date: Tuesday, July 10th, 2007
Time: 8:00 AM