Bryological and Lichenological Section/ABLS
Mansouri, Katayoun , Renzaglia, Karen S. .
Studies of plasmodesmata in geometrically diverse apical cells of bryophytes.
Across bryophytes, there are four distinct apical cell geometries that are responsible for growth of the gametophyte: lenticular, tetrahedral, wedge-shaped and hemidiscoid. All four types are present in the morphologically diverse liverworts, while in mosses tetrahedral cells predominate. Leafy and thalloid growth forms of both mosses and liverworts are correlated with these geometries in a way that each apical derivative (merophyte) gives rise to a leaf, leaf-like structure or portion of a thallus wing. The arrangement of these organs follows the shape of the apical cell. For example, tetrahedral cells have three cutting faces from which three rows of leaves originate in liverworts. In this study apical meristems of Pellia epiphylla and Bazzania trilobata representing two clades in liverworts with hemidiscoid and tetrahedral apical cell geometries, respectively, were examined by light, scanning and transmission electron microscopes. Both species of Takakia, an early divergent moss with a tetrahedral apical cell and irregular leaf-like appendages (phyllids), were examined as well. General cytological features of apical cells and their immediate derivatives were documented for each taxon. In addition, plasmodesmatal ultrastructure and density were recorded for apical cell and merophyte walls. Only simple plasmodesmata and no secondary, H-shaped or branched plasmodesmata were observed. In all species, plasmodesmatal density is greatest in apical cell walls, even though cell divisions often are infrequent in the apical cell. The density in apical cells is also higher than in any recently formed walls within developing merophytes; this suggests the decrease in plasmodesmata is not due solely to the cell wall expansion that occurs during differentiation. Thus, regardless of geometry, apical cells in bryophytes contain abundantly more plasmodesmata than derivatives, supporting the concept that this cell not only produces merophytes but also is responsible for coordinating morphogenetic events through symplastic connections.
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1 - Southern Illinois University Carbondale, Plant Biology, Life Science II 459, Carbondale, IL, 62901, USA
2 - Southern Illinois University, Department of Plant Biology, 1125 Lincoln Drive, Carbondale, Illinois, 62901-6509, USA
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Magpie B/Cliff Lodge - Level B
Date: Monday, July 27th, 2009
Time: 4:00 PM