VIEW ARTICLE

Fine Structure of the Host-Parasite Interface of Plasmodiophora brassicae in Cabbage. Paul H. Williams, Associate Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706; Sharon S. McNabola, Research Specialist, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 60:1557-1561. Accepted for publication 1 June 1970. DOI: 10.1094/Phyto-60-1557.

Under the electron microscope the parasitic stages of Plasmodiophora brassicae are surrounded by a plasmodial envelope which appears as a seven-layered boundary approximately 230 å thick comprising four uniformly spaced electron-dense layers separated by three electron-lucent layers. Densitometric tracings of glutaraldehyde-acrolein-fixed and osmium-uranium-lead-stained plasmodia within the cell and isolated from the host indicated that the inner layers of the envelope were slightly thicker and more heavily stained than the layers adjacent to the host and parasite cytoplasm. Upon extraction of the polar lipids from the envelope prior to heavy metal staining, the stained layers were comprised of globular stain deposits about 30-40 å across. After complete extraction of lipid with pyridine, the integrity of the individual layers was lost; however, the envelope persisted as a prominent boundary of stain deposits, presumably on proteinaceous components of the membranes. The envelope is viewed as two closely appressed unit membranes, each with a sectional dimension close to that of the host plasma membrane but differing in thickness from the other cytomembranes of the cell and plasmodium. Although unproven, the outer membrane of the envelope was thought to originate through the invagination of the host membrane at the time of plasmodial penetration of the cell.