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(American Journal of Botany. 2008;95:643-654.)
doi: 10.3732/ajb.2007210
© 2008 Botanical Society of America, Inc.
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Anatomy and Morphology

Patterns of cell division in the filamentous Desmidiaceae, close green algal relatives of land plants1

John D. Hall2,4,5, Richard M. McCourt3 and Charles F. Delwiche4

2 Cullman Program for Molecular Systematics Studies, New York Botanical Garden, Bronx, New York 10458 USA 3 Department of Botany, Academy of Natural Sciences, 1900 Benjamin Franklin Parkway, Philadelphia, Pennsylvania 19103 USA 4 Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, Maryland 20742 USA

ABSTRACT

Patterns of cell division and cross wall formation vary among the charophytes, green algae closely related to land plants. One group of charophytes, the conjugating green algae (Zygnematophyceae), is species-rich and is known to vary substantially in the mode of cell division, but the details of these cell division patterns and their phylogenetic distribution remain poorly understood. We studied cross wall development in filamentous Desmidiaceae (a clade of conjugating green algae) using differential interference contrast and fluorescence light microscopy. All strains investigated had centripetal encroachment of a septum, but with several different developmental patterns. In most cases, cell wall formation was delayed with respect to the Cosmarium-type of cell division, and the cross wall was modified considerably after deposition in a manner specific to the particular clade of filamentous desmids. These characteristics were mapped on a phylogeny estimated from a data set of two organellar genes, and the evolutionary implications of the character state distribution were evaluated. The data suggest a complex history of evolution of cell division in this lineage and also imply that Desmidium and Spondylosium are polyphyletic. These results indicate that many features of the cell shape are determined at the time of cell division in conjugating green algae.

Key Words: Desmidiaceae • cell division • coxIII • development • rbcL • septum formation • Zygnematophyceae






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