Structural differences between two types of basidiomycete septal pore caps.
The septal pore cap (SPC) of Trichosporon sporotrichoides CBS 8245 is vesicular-tubular, connected with flat-tubular endoplasmic reticulum (ER), and stains densely with zinc/iodine/osmium tetroxide, as does the ER. The SPC of Schizophyllum commune CBS 340.81 is more complex, about 600 nm in diameter, with perforations of 80-120 nm diameter, and stains less densely with zinc/iodine/osmium tetroxide than the ER. In high-pressure frozen and freeze-substituted hyphae of T. sporotrichoides the ER is present parallel to the dolipore septa, and electron-dense material occurs opposite the septal pore channel; the SPC rarely showed smooth vesicular-tubular membranes, suggesting that this is an ephemeral function of the SPC. The SPC of S. commune has a smooth outer and inner membrane, which enclose a matrix with a palisade-like substructure. A thin layer of electron-dense material covers the inner surface of the SPC of S. commune, from which beaded filamentous structures connect the SPC and the pore-occluding material. These filamentous structures may maintain the intracellular position of the SPC and possibly play a role in plugging the septal pore channel. The septal pore swellings of T. sporotrichoides contain more 1,6-beta-glucan than the septum, and intracellular glucans are also present near the septal pore channel. This cytosolic 1,6-beta-glucan in T. sporotrichoides may serve as a matrix to keep the tubular membranous structures of the SPC together. In contrast, 1,6-beta-glucan is not observed in the SPC and in the pore-occluding material of S. commune, and hyphal septa of this species show less labelling of 1,6-beta-glucan than the septal swelling. The evolutionary transition from simple to more complex types of SPCs may have resulted in a requirement for different components to maintain the morphological integrity and cell biological function.
Yeast Division of the Centraalbureau voor SchimmelculturesJulianalaan 67, 2628 BC DelftThe Netherlands.|Department of Molecular Cell Biology, EMSA, Utrecht UniversityPadualaan 8, 3584 CH UtrechtThe Netherlands.
Wally H
WH
Müller
Centre for Fungal Cell Wall Research, Institute of Molecular Cell Biology, University of Amsterdam1098 SM AmsterdamThe Netherlands.
Roy C
RC
Montijn
Department of Molecular Cell Biology, EMSA, Utrecht UniversityPadualaan 8, 3584 CH UtrechtThe Netherlands.
Bruno M
BM
Humbel
Department of Plant Cytology and Morphology, Agricultural University of WageningenArboretumlaan 4, 6703 BD WageningenThe Netherlands.
Adriaan C
AC
van Aelst
Department of Molecular Cell Biology, EMSA, Utrecht UniversityPadualaan 8, 3584 CH UtrechtThe Netherlands.
Eline J M C
EJMC
Boon
Department of Molecular Cell Biology, EMSA, Utrecht UniversityPadualaan 8, 3584 CH UtrechtThe Netherlands.
Theo P
TP
van der Krift
Yeast Division of the Centraalbureau voor SchimmelculturesJulianalaan 67, 2628 BC DelftThe Netherlands.
Teun
T
Boekhout
D001487:Basidiomycota / Q000648:ultrastructure*; D005615:Freezing; D005936:Glucans / Q000032:analysis; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D009993:Osmium Tetroxide; D012567:Schizophyllum / Q000648:ultrastructure; D013194:Staining and Labeling; D014250:Trichosporon / Q000648:ultrastructure
D005936:Glucans; D009993:Osmium Tetroxide