GEOSIPHON-PYRIFORME, AN ENDOSYMBIOTIC ASSOCIATION OF FUNGUS AND CYANOBACTERIA - THE SPORE STRUCTURE RESEMBLES THAT OF ARBUSCULAR MYCORRHIZAL (AM) FUNGI
A. Schussler et al., GEOSIPHON-PYRIFORME, AN ENDOSYMBIOTIC ASSOCIATION OF FUNGUS AND CYANOBACTERIA - THE SPORE STRUCTURE RESEMBLES THAT OF ARBUSCULAR MYCORRHIZAL (AM) FUNGI, Botanica acta, 107(1), 1994, pp. 36-45
The zygomycete Geosiphon pyriforme is the only known endocyanosis of a
fungus. The Nostoc spp. filaments are included in photosynthetically
active and nitrogen fixing, multinucleated bladders, which grow on the
soil surface. The spores of the fungus are white or slightly brownish
. They are about 250 mum in diameter and develop singly on hyphal ends
or, less frequently, intercalarly. The wall of the spores consists of
a thin innermost layer, a laminated inner layer with a thickness of a
bout 10-13 mum, and an evanescent outer layer. The laminated layer is
composed of helicoidally arranged microfibrils, and is separated from
the evanescent outer layer by a thin electron-dense sub-layer. Polaris
ation microscopy indicates the occurrence of chitin. Shape and wall ul
trastructure of the Geosiphon spores and their cytoplasm resemble that
of Glomus spores, but are different from that of other genera of the
Glomales and Endogonales. Germination occurs by a single thick hyphal
outgrowth directly through the spore wall. Like various AM forming fun
gi, Geosiphon pyriforme contains endocytic bacteria-like organisms, wh
ich are not surrounded by a host membrane. Our observations indicate t
hat Geosiphon is a potential AM fungus.