Enzyme activities of the internal hyphae and germinated spores of an arbuscular mycorrhizal fungus, Gigaspora margarita Becker & Hall

SUMMARY A method for isolation of metabolically active internal hyphae from arbuscular mycorrhizas of onion (Allium cepa) is described. Roots of onion plants colonized by Gigaspora margarita were treated with a digestion solution containing cellulase and pectinase for 1 h at 30 °C, then homogenized with a Waring blender at low speed. The internal hyphae were collected from the homogenate by centrifugation on a discontinuous gradient of Percoll, then purified further by filtration. Enzyme histo chemical staining showed that the collected internal hyphae had active succinate dehydrogenase (SDH), alkaline and acid phosphatases (ALP, ACP). Specific activities (protein basis) of several enzymes in a crude extract of the internal hyphae were compared to those of axenically germinated spores of G. margarita. The specific activities of hexokinase, and of the enzymes involved in phosphate metabolism (ALP, ACP) and the TCA cycle (SDH, malate dehydrogenase) were much greater in the internal hyphae than in the germinated spores. The specific activity of phosphofructokinase was similar in both. By contrast, the specific activity of glucose‐6‐phosphate dehydrogenase was higher in the germinated spores. The metabolic change from non‐symbiotic to symbiotic status of the fungus is discussed in relation to these results.