A COMPARATIVE ULTRASTRUCTURAL-STUDY OF ENDOPHYTIC BASIDIOMYCETES IN THE PARASITIC ACHLOROPHYLLOUS HEPATIC CRYPTOTHALLUS-MIRABILIS AND THE CLOSELY ALLIED PHOTOSYNTHETIC SPECIES ANEURA-PINGUIS (METZGERIALES)

This ultrastructural study of two closely related liverworts with cont rasting modes of nutrition reveals very similar interactions with endo phytic dikaryotic basidiomycetes. In both hepatics, collected from a v ariety of sites, the fungus is confined to specific regions of the gam etophyte thallus, and hyphal contact with the substratum is via the rh izoids. The colonization cycle comprises a growth phase when the fungu s forms large intracellular coils, host cytoplasm proliferates and the starch content of the plastids decreases, followed by senescence when the hyphae die back and aggregate into large masses. Repeated coloniz ation cycles are frequent. Young hyphae contain abundant glycogen and sometimes amyloid deposits in Cryptothallus. In terms of dolipore subs tructure, hyphal dimensions, highly characteristic multilayered walls, absence of clamp connections, and die mode of hyphal degeneration, th e endophyte in Cryptothallus is virtually identical to that in Aneura from alpine sites but very different from the fungus in Aneura from sa nd dunes and a chalk pit. It is suggested that Cryptothallus evolved f rom an Aneura-like ancestor through association with a fungal saprophy te of waterlogged peaty soils. Differences in dolipore morphology in t he ectomycorrhizal fungus of Betula roots growing in association with Cryptothallus indicate that these two hosts do not share the same fung us. Remarkable similarities between the fungal associations in Cryptot hallus and Aneura and orchidaceous mycorrhizae include the same coloni zation cycle, absence of polyphosphate granules, and separation of the host plasma membrane from thin-walled, exclusively intracellular hyph ae by a prominent interfacial matrix.