FLAGELLAR APPARATUS AND STRIATED RHIZOPLAST OF ZOOSPORE OF OLPIDIUM-BRASSICAE

The flagellar apparatus and its associated structures of the zoospore of O. brassicae are described and compared with observations of other zoospores of the uniflagellate Phycomycetes. The zoospore of O. brassicae is shown to have an extensive cone-shaped rhizoplast fused to both the functional and the vestigial kinetosomes. Three-dimensional reconstructions were made of the kinetosomal region. The vestigial kinetosome differs from the functional, as it only has triplet bundles of microtubules and it lacks a system of props. The proximal termination of the central pair of flagellar microtubules occurs within the axoneme. No terminal plate is observed. The occurrence of dictyosomes in the Chytridiales, Monoblepharidales and Hyphochytriales is discussed and it is concluded that a dictyosome may be present in the encysting zoospore and the maturing zoosporangium of O. brassicae but only vestiges of a dictyosome are found in the free-swimming zoospore.