| Popis: |
Electron-microscope studies demonstrate that presporangial cells (hypnospores) of the fungus Dermocystidium marinum are characterized by an apparent lack of mitochondria, by a cell wall homogeneous with respect to electron density, and by an electron-light nucleus. In precleavage sporangia, morphogenesis of mitochondria appears to occur from myelin figures, the cell walls acquire a three-layered appearance, and the nuclei become electron-dense with evidences of condensed chromatin. A discharge pore and tube are formed by rupture of the cell wall and subsequent unfolding of the tube from the innermost part of the cell wall. The pore is blocked by a plug which is a thickened section of the inner cell wall. Sporulation proceeds by successive bipartition of the protoplast involving alternating karyokinesis and cytokinesis. The nuclear membrane persists during karyokinesis. The process terminates with the formation of billagellated planonts, enclosed by two unit membranes. Evaginations of one or both of the membranes form a row of tinsels along one side of the anterior flagellum. Golgi bodies and a previously undescribed, electrondense body are found next to the planont nucleus. D. marinum is concluded to be a member of the Saprolegniales on the basis of planont morphology and previously described stages. |
