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Electron microscope study of a mycelial mutant of Ustilago hordei (Pers.) Lagerh. Stein, Carla Winnifred


A mutant mycelial colony of Ustilago hordei (Pers.) Lagerh.' was studied by light and electron microscopy to compare its general morphology with results obtained from earlier cytological studies. Its ultrastructure is also compared with that of other fungi. The results obtained from light microscopy generally agree with those from earlier work. Cells of the mycelia are very long, irregular in length, and contain numerous mitochondria and one to several nuclei. Electron microscopy reveals the walls of the mycelial cells to be single layered fibrillar structures. In apical regions all the characteristic organelles are present. The elongate mitochondria have plate-like cristae that lie parallel to the long axis of the mitochondri and the outer bounding membrane is often thicker than the inner one; these two features of the mitochondria are both unusual. Endoplasmic reticulum is sparse. Branch hyphae and septae are not present. In differentiated areas there is an increase in the number of vesicles and larger vacuoles. Mitochondria undergo rather unique changes whereby concentric lamellae are formed in a bulge of outer mitochondrial membrane. These concentric lamellae are engulfed by vacuoles in which the lamellae appear to be transformed into tubular bodies. At some point these vacuoles fuse with the plasma membrane and release their contents into the space between the plasma membrane and the cell wall. The vacuoles seem to act as lysosomes. Branch hyphae and septae are present. Degenerate regions are very vacuolated and contain many membranous structures. Few organelles are present. Mitochondria are distorted and their cristae swollen or absent. Dictyosomes and lomasomes are not present throughout the hyphae.

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