Connexions cortex–paroi chez la cellule apicale de Sphacelaria

Abstract

The apical cell of Sphacelaria (Fucophyceae) exhibits a permanent polarized organization throughout asymmetric divisions. The apex organization was studied by immunolocalization of tubulin, vitronectin, α-actinin and β1 integrin. Microfilaments were stained directly by fluorescein phalloidin. The apex was highly organized around a patch of microfilaments densely packed at the tip, where vitronectin-like and α-actinin-like proteins colocalized. In the same area, an actin-dependent targeted secretion of sulfated polysaccharides was shown. The permanent localization of these components throughout cell elongation suggests that a cortical site involving transmembrane connections between the cytoskeleton and the extracellular matrix is required for cell polarity. A model of the organization of the tip is proposed.