The ultrastructure of Olpidium brassicae. I. Formation of sporangia

Abstract

The ultrastructure of Olpidium brassicae was observed in epidermal cells of lettuce roots from 8 h after inoculation with zoospores until the thalli matured, at 72 h. In early stages of growth the thallus is completely surrounded by the host cytoplasm and separated from it by the thallus ectoplast. A thallus wall begins to form after 36 h and consists of three layers. The thallus contains the usual organelles, a nucleus (many nuclei after about 24 h), mitochondria, ribosomes, and lipid globules. Membrane-bounded structures, the multivesicular bodies, occur throughout the life cycle and are thought to be involved in synthesis of glycogen and lipid, and at a later stage in cleavage of the thallus protoplasm into zoospore protoplasts. One kinetosome in each zoospore protoplast produces a flagellum that is pushed into the cleavage vacuole. An exit tube originates from a bulge in the thallus wall and is closed by an elaborate plug.

The ultrastructure of Olpidium brassicae. II. Zoospores

“…since they carry viruses to healthy plants. This report on the ultrastructure of 0. brassicae zoospores extends previous observations on the Observations development of the thallus (17).…”

“…Also present are a series of structures of variable appearance (Figs. 9-12) that seem to be homologous with the multivesicular bodies observed in thalli (17). They have a single membrane surrounding an area consisting of a varying number of small vesicles.…”

“…A kinetosome, a centriole, and a rhizoplast complete the kinetid, which is deMaterials and Methods scribed in detail below. At one side of the 0. brassicae was grown and maintained as previously axoneme the zoospore body has a lobe which is described (17). Zoospores were discharged into tap water Seen only in longitudinal perpendicular or 0.05 M glycine and fixed within 15 minutes of dis-to a plane running through the kinetosome and charge by either of two methods.…”

The Fine Structure of Germinating Resting Spores of Olpidium brassicae.

“…Zoosporangia and resting spores develop in the epidermal and cortical cells of plant roots following infection of the cells by zoospores. While the ultrastructure of zoospores and zoosporangia of 0. brassicae has been studied in detail (Temmink and Campbell, 1968, 1969a, 1969bLesemann andFuchs, 1970a, 1970b;Temmink, 1971), information concerning the resting spore formation and germination at the ultrastructural level has been limited (Hiruki and Alderson,1976;Hiruki, 1987Hiruki, , 1990. This paper reports the results of observations on the fine structure of germinating resting spores of 0. brassicae by scanning and transmission electron microscopy.…”

Epidemiología y variabilidad patogénica del virus del mosaico del pepino dulce (Pepino mosaic virus). Nuevas enfermedades asociadas a su presencia (torrao o cribado)

“…The thallus becomes embedded in the host cytoplasm and later develops into either a thin-walled zoosporangium or a thick-walled stellate resting spore. When mature, zoosporangia release zoospores through exit tubers and the life cycle is repeated (Campbell, 1996;Temmink and Campbell, 1968).…”