ANALYSIS OF THE CELL-CYCLE IN AN ARBUSCULAR MYCORRHIZAL FUNGUS BY FLOW-CYTOMETRY AND BROMODEOXYURIDINE LABELING

The cell cycle of an arbuscular mycorrhizal fungus, Glomus versiforme, was determined by flow cytometric analysis of nuclei isolated from spores and mycorrhizal roots of leek, and by immunogold staining after bromodeoxyuridine (BrdU) uptake by DNA. The aims of our work were to establish: (i) whether there are changes in ploidy during fungal growth and morphogenesis, (ii) when and where the cell cycle is activated. Our results demonstrate that nuclei isolated from quiescent spores of G. versiforme are arrested in the G0/G1 phase (99.2%), whereas fungal nuclei from mycorrhizal roots are in the synthetic (S) (10.1%) and G2/M phase (3.9%). Nuclei undergoing DNA synthesis were detected in situ after BrdU uptake. Labelled nuclei were observed in intercellular hyphae and in large arbuscular trunks. This paper demonstrates that colonization of an arbuscular mycorrhizal fungus is linked to activation of its cell cycle.