Apical control of band elongation in Antithamnion defectum (Ceramiaceae, Rhodophyta)

Abstract

Cell elongation in the Ceramiaceae typically occurs by means of one or two bands located apically and (or) basally in each cell. In axial cells of Antithamnion defectum two bands are present; however, most cell elongation occurs as a result of new wall deposition in bands at the base of each axial cell. In cells of determinate branches, only the basal band is present. In experimental conditions in which apical cells of indeterminate branches are differentially excised, location of the primary elongation band can be reestablished in relation to remaining indeterminate axes. Thus, the primary elongation band in axial cells is always basal with respect to indeterminate apical cells. When all indeterminate apices are removed, band growth becomes highly disrupted, and diffuse, irregularly located bands are formed. These results suggest that regulation of band position and elongation is through apical control.