The Dolipore/Parenthesome Septum in Modern Taxonomy

Abstract

Fungal septa are a consequence of opposing layers of wall material being deposited between opposite faces of a centripetally invaginating membrane. Septa are entire in the aquatic fungi and most of the zygomycetes, but are generally perforate in the higher fungi (Moore, 1994). It is not known how cytokinesis terminates in a central pore. Ascomycete septa are homogeneous, electron translucent; the pores have rounded edges, are of a size to allow nuclear migration, and are accompanied by one or more Woronin bodies on either side that are large enough to block the pore (Buller, 1933; Markham and Collinge, 1987). Basidiomycete septa, however, are tripartite and appear light-dark-light layered when viewed electron microscopically (e.g., Bracker and Butler, 1963). The essential compositional difference between ascomycete and basidiomycete septal morphology was first noted by Kreger-van Rij and Veenhuis (1971) and is now recognized to be a fundamental indicator of the two subkingdoms (Table 1). This dichotomy also occurs in the walls and is most useful in determining the taxonomic affinities of yeast phases where the distinction is diagnostic during budding (see Moore, 1989c; 1996b).