Ultrastructure of Septa in Dimargaris cristalligena R. K. Benjamin

Summary: The fine structure of the septum in the vegetative hypha of the mycoparasite Dimargaris cristalligena is described. The cross-wall, continuous with the inner electron-lucent layer of the hyphal wall, bears a central pore with a flared margin occupied by a biumbonate electron-dense plug. A globose body, surrounded by a zone of ribosome-free cytoplasm, is situated next to the septal pore on each side of the cross-wall. In the neck of the haustorium, a globose body is normally observed only on that side of the septal pore next to the appressorium. Globose bodies appear structureless; they are electron-dense when fixed in potassium permanganate and of variable electron density in aldehyde-osmium fixations. Cytoplasmic continuity is maintained through the septal pore by the plasmalemma. In the sporangiophore and sporiferous branchlets, the septal plug bears an upper globose pro-tuberance and a lower obconic one. The hyphal septum in Tiegherniomyces californicus is ultrastructurally similar to that of D. cristalligena. The possible functional and taxonomic significance of such septa is indicated.