Localization of β (1 → 3) glucans in spore and hyphal walls of fungi in the Glomales

Abstract

Endomycorrhizal fungi in Glomales have been classified as Zygomycetes, which generally have chitin and chitosan as cell wall components. Preliminary evidence suggested that the wall of at least one Glomus species possessed β (1 → 3) glucan polymers. A wider range of taxa representative of each of the four genera in Glomales were analyzed for presence or absence of β (1 → 3) glucans using indirect immunolabelling with commercial monoclonal and polyclonal antibodies specific for β (1 → 3) oligoglucosides. These structural polysaccharides were present in selected Glomus and Acaulospora species, but they were not detected in Gigaspora or Scutellospora species. The β (1 → 3) glucan polymers were localized in the inner wall of external hyphae and germ tubes, as well as in the spore wall. The presence of chitin was confirmed in all genera. The distribution of β (1 → 3) glucans among genera suggests that vesicular-arbuscular fungi in the suborder Glomineae (Glomus and Acaulospora) may represent, as Entomophthorales, an outlying group in the Zygomycetes with uncertain phylogenetic relationships. Only arbuscular fungi in Gigasporineae (Gigaspora and Scutellospora) would remain firmly placed in the Zygomycetes.

Key Words:

• β (1 → 3) glucans
• Glomales
• phylogeny
• walls