Ultrastructure of Septa in Tieghemiomyces californicus

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Abstract
Septa in the sporangiophore of T. californicus, as revealed by light, scanning and transmission electron microscopy, comprise a crosswall with a flared, lenticular central pore region which encloses an electron-dense biumbonate plug. On each side of the septum and closely associated with the central plug, is an amorphous, electron-dense, globose body lacking a bounding membrane. The crosswall consists of a central, sometimes stratified, electron-lucent layer overlain by an electron-dense layer. Septa in the vegetative hypha are structurally similar. The sporangiophore is liberated through rupture of a subseptal annular zone of weakness below the sporulating branches on the main, vertical axis of the sporangiophore. The septal complexes remaining in the disrupted sporangiophores serve to maintain the colony of the parasite in a functional state upon the host by preventing the mass egress of cytoplasm. The fine structure of the septum in T. californicus is fundamentally similar to that found in the vegetative hypha of Dimargaris cristalligena and the sporangiophore of Dimargaris verticillata and Dispira cornuta, which supports the use of this character as diagnostic of the Dimargaritales.