Summary
The spore wall in the smut fungus Entorrhiza has been investigated, with particular reference to layer 3. The wall is stratified into four layers, numbered 1–4 from the outside to inside of the wall. Layer 3 has a lamellated or striated organization, depending on the type of specimen preparation used for examination. In this study, thin sectioning and freeze-etching methods were used in transmission electron microscopy. Layer 3 is approximately 50 nm thick and is the narrowest layer of the wall. Thin sections viewed at high magnification show a lamellated organization, consisting of alternate electron dense and translucent spaces. Usually between 16–20 lamellae form the layer, with a lamella having a thickness of about 1–2 nm. At high resolution, each electron dense lamella is resolved as a row of closely packed subunits, approximately 1.5 nm in diameter. The electron translucent lamellae probably represent mainly lipoidal material, which is extracted during specimen preparation. In freeze-etch preparations layer 3 is termed the “striated layer”. Fracturing exposes face views of the layer, which at low magnification has a wrinkled appearance. At high magnification, layer 3 has a structure consisting of an irregular mosaic of striations. The striations in each area of the mosaic are arranged parallel, and regularly spaced 11–13 nm apart. Each area of the mosaic is separated from an adjacent area by a small step; this represents where the plane of fracture changed to a different level within layer 3. Fracturing probably occurs in the lipoidal region of the layer, corresponding to the electron translucent lamellae seen in thin section. At high magnification, the striations are resolved into subunit-like particles, approximately 1–2 nm in diameter. Layer 3 is believed to form an impervious region in the spore wall. Layer 3 in Entorrhiza closely resembles the “partition layer” reported in spores of other Tilletiaceae. This demonstration of a common wall layer strengthens the relationship between Entorrhiza and the rest of the Tilletiaceae. Entorrhiza is the only smut that forms galls on host roots.
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Fineran, B.A. A lamellated striated layer in the spore wall of the smut fungus Entorrhiza (Ustilaginales). Protoplasma 173, 58–69 (1993). https://doi.org/10.1007/BF01378862
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DOI: https://doi.org/10.1007/BF01378862