The three-dimensional structure of the flagellar apparatus of Chrysosphaerella brevispina (Chrysophyceae) as viewed by high voltage electron microscopy stereo pairs

Abstract

Stereo-pair micrographs of thick sections, using high voltage electron microscopy as well as conventional electron microscopy, are used to examine the flagellar apparatus of Chrysosphaerella brevispina, a silica-scaled alga. This follows the general pattern found among the Chrysophyceae, but differs from that found among the silica-scaled Synurophyceae, providing further evidence for the separation of these two classes. A delicate rhizoplast is present in Chrysosphaerella, but it extends towards a mitochondrion and the plasma membrane rather than towards the nucleus. The R, microtubular root forms a broadly sweeping arc with numerous cytoskeletal microtubules spreading out from it. The R₂ root consists of two microtubules that pass over the chloroplast on the left side of the cell. The R₃ and R₄ microtubular roots form antiparallel loops around and under the short flagellum. The R₄ root originates on the anterior surface of the short flagellum. The R₃ root originates near the axis of the basal bodies on the right side of the cell. At its origin, the root consists of six microtubules arranged in a trough-like cluster; one microtubule separates from the cluster and loops around and under the short flagellum, probably terminating on the upper surface of the basal body of the short flagellum. Of the remaining five microtubules, three extend only a short distance. The other two loop under the short flagellum and curve back to the basal bodies, one passing under the basal bodies and coiling on the anterior surface of the nucleus.