Ordered septin filaments are paired, align parallel to the cell growth axis, and are dynamic. (A) A. gossypii cells expressing Cdc12-conGFP4 were treated with the septin filament stabilizing drug FCF. The mean GFP dipole orientation in septin fibers was found to be perpendicular to the fiber axis. Cell outlines are shown in white. Bar, 1 µm. (B) A. gossypii cells (AG127) were treated for 3 h with FCF and processed for TEM. A typical filament and a magnified section are displayed. Brackets point to the measured width and periodicity of a population of septin filaments gathered from many different sections accompanied by standard deviations (statistics are given in Table S1). PM, plasma membrane; CW, cell wall. (C) An immunolabeled section of SHS1-6HA–expressing cells (AG296) in which septins have been localized using an anti-HA primary and a 10-nm gold conjugated secondary antibody. Arrowheads point to gold particles. Bar, 100 nm. (D) A. gossypii cells expressing Cdc12-conGFP4 or Cdc3-conGFP exhibit GFP dipoles oriented parallel to the cell cortex when imaged in cross section (xz plane). Cell outlines are shown in white. Bars, 1 µm. (E) A septin ring in A. gossypii expressing Cdc12-conGFP4 was analyzed, photobleached and analyzed, and allowed to recover before repeat of analysis. The recovered signal is ordered and reports the same GFP dipole orientation (perpendicular to the cell growth axis) as the starting ring. Bar, 1 µm.