Structural differences between two types of basidiomycete septal pore caps

Abstract

The septal pore cap (SPC) of Trichosporon sporotrichoides CBS 8245 is vesiculartubular, connected with flat-tubular endoplasmic reticulum (ER), and stains densely with zinc/iodine/osmium tetroxide, as does the ER. The SPC of Schizophy//um commune CBS 340.81 is more complex, about 600 nm in diameter, with perforations of 80-120 nm diameter, and stains less densely with zincliodinelosmium 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 5. 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. Eporotrichoides contain more 1,6-/?=glucan than the septum, and intracellular glucans are also present near the septal pore channel. This cytosolic 1,6-/&glucan in T. Jporotrichoides may serve as a matrix to keep the tubular membranous structures of the SPC together. In contrast, 1,6-Pglucan 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-/&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.

Septal Pore Cap Protein SPC18, Isolated from the Basidiomycetous Fungus Rhizoctonia solani , Also Resides in Pore Plugs

“…Mycelia were high-pressure frozen and freeze-substituted (36). Sections of about 90 nm and 350 nm were contrasted with 4% (wt/vol) aqueous uranyl acetate (Merck) for 10 min and with 0.4% (wt/vol) aqueous lead citrate (Merck) for 2 min (54).…”

“…The Agaricomycotina fungi, on the other hand, are characterized by septa that are flared toward the pore, forming a barrel-shaped structure, the dolipore, and are associated with SPCs (9,17,21,35,37,39). The endoplasmic reticulum (ER) is connected at the base of the SPC, thus suggesting that the SPC is a subdomain of the ER (9,18,36). The ultrastructure of SPCs has been studied extensively, and based on these observations, several functions of the SPC have been proposed.…”

Physiological Significance of Network Organization in Fungi

“…In N. crassa, the septal pores are open, and the cytoplasm and all organelles, including nuclei, show dramatic flow rates through interconnected networks (33). Other species, such as many filamentous basidiomycetes, have complex structures at the septa that allow cytoplasmic and presumably some organellar transfer but which restrict nuclear mixing (46). Additionally, some basidiomycete species can form multihyphal aggregates, termed cords or rhizomorphs, that show some tissue differentiation, with larger-vessel hyphae acting as conduits for long-distance transport (14,32).…”

Field‐emission scanning electron microscopy of the internal cellular organization of fungi

“…Furthermore, fractured cells at the periphery of the globules were difficult to view with the SEM because the fungal hypha charged and moved during imaging. These problems were successfully overcome by growing fungi between PCTE filters on agar medium in Petri dishes (Müller et al 1998a(Müller et al , 1998b. Fixation and postfixation of fungi allowed us to cut the colony into segments for freeze-fracturing.…”

“…Several plant tissues have also been subjected to internal visualization, including the alga Euglena (Guttman 1971), chloroplasts (Barnes and Blackmore 1984a, b), and roots (Van Aelst and Wilms 1988;Vesk et al 1994Vesk et al , 1996. By contrast, only a few studies reported on fungal material, such as interactions with host tissues , formation of arthrospores (Barrera 1983), and septal pore caps in basidiomycetes (Lisker et al 1975;Müller et al 1994Müller et al , 1995Müller et al , 1998aMüller et al , b, 1999.…”