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Phycological Section

Kocot, Kevin M. [1], Betzelberger, Amy M. [1], Doty, Karen F. [1], Cook, Martha E. [1].

Ultrastructure and Morphology of Development in the Charophycean Green Alga Chaetosphaeridium (Coleochaetales).

Chaetosphaeridium, the sister taxon to Coleochaete, has sometimes been mistaken for a unicellular organism. Instead, it is a branched filament with an unusual developmental process in which a spherical cell divides almost parallel to its substrate, after which the lower cell bulges laterally to re-orient itself into an adjacent position. The cells of the thallus remain connected by layers of wall material. Our previous studies using calcofluor staining of cellulose showed that wall growth in the bulging cells of Chaetosphaeridium is directed growth in one part of the cell, rather than expansion along the length of the cell, and hence might be termed tip growth. With immunolocalization of tubulin we demonstrated a microtubule pattern in bulging cells that resembles that of tip growth and also reported cytokinesis by means of a phragmoplast. Our recent TEM studies confirm directed cell growth, with the position of scales from zoospores that developed into vegetative cells distinguishing between the initial cell wall and subsequent growth. TEM also reveals the presence of plasmodesmata. Preliminary studies using differential interference constrast (DIC) microscopy suggest that cell plate formation in Chaetosphaeridium, which like that of Coleochaete must accommodate a large vacuole and a single large chloroplast, could be termed polar cytokinesis as described for higher plants. Unlike in Coleochaete, however, the dividing cells of Chaetosphaeridium are spherical and the forming cell plates are oriented to accommodate the unusual mechanism of thallus development. Correlated studies using light and electron microscopy increase our understanding of growth phenomena in the Coleochaetales and may shed light on the evolution of plant growth and development.


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1 - Illinois State University, Department of Biological Sciences, Campus Box 4120, Normal, Illinois, 61790-4120, USA

Keywords:
cell division
Chaetosphaeridium
charophycean algae
Coleochaete
development
evolution
plasmodesmata.

Presentation Type: Poster
Session: 33-69
Location: Salon C, D & E - Gov Ballroom/Hilton
Date: Tuesday, August 16th, 2005
Time: 12:30 PM
Abstract ID:437


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