Actin rings in cytokinesis of apical cells in red algae

Abstract

Actin rings are demonstrated for the first time in florideophyte red algae in Audouinella botryocarpa (Acrochaetiales) and Tiffaniella snyderae and Griffithsia pacifica (Ceramiales). Rings formed a complete circle in the peripheral cytoplasm prior to the development of the septum by furrowing. In the uninucleate A. botryocarpa, ring formation precedes mitosis. In all species F-actin initially has a diffuse to longitudinal alignment throughout the cell. The actin realigns and then contracts to form a dense actin ring. Following cell division, aggregations of actin are maintained along the transverse wall in at least G. pacifica and A. botryocarpa, and a dense ring of actin was observed around a pit plug in T. snyderae. The occurrence of actin rings in cell division of members of the Acrochaetiales and Ceramiales is consistent with ultrastructural observations on red algal unicells and suggests that actin rings are part of the ancestral cytokinetic mechanism in red algae. Keywords: actin rings, cell division, cytokinesis, cytoskeleton, microfilaments, Rhodophyta.