Germination of Glomus mosseae Spores: Procedure and Ultrastructural Analysis

Abstract

We analyzed structures produced by the germinated spores of Glomus mosseae. Freshly isolated spores germinated (0%-80%) within 14 d at 22 C on sterile, Hoagland's agar-coated coverslips and produced branching intrahyphal proliferation with occasional septa and secondary spores. Hyphae contained mitochondria, lipid droplets, and numerous elongated nuclei with nucleoli. Hyphal walls represented multiple wall layering from invasion of old empty walls by new hyphae. Direct germination was seen in spores incubated near corn roots growing in sand/liquid nutrient culture. This is the first report of intrahyphal proliferation occurring in non-host-associated vesicular arbuscular mycorrhizae (VAM) and of direct germination occurring in G. mosseae. Bacterium-like organelles (BLOs) were present in two other VAM species analyzed ultrastructurally. Occasional imperforate septa were observed. Secondary spores, produced by hyphal branches most proximal to the primary spore, contained nuclei, mitochondria, BLOs, lipid droplets, and vacuoles and had walls similar to that of the hypha. Unlike the two previous ultrastructural studies of VAM, no membrane-bound crystals were seen in 14-d-old G. mosseae hyphae or secondary spores.