STATUS OF NUCLEAR DIVISION IN ARBUSCULAR MYCORRHIZAL FUNGI DURING IN-VITRO DEVELOPMENT

The number of nuclei in spores and along hyphae of an arbuscular mycor rhizal fungi Gigaspora margarita was measured in digital images of flu orescence arising from mithramycin stained cultures. Typical dormant s pores (250 mum diameter) contained 2000 nuclei. Eight hundred nuclei w ere mobilized during the first 3 days of germination. The number of nu clei in the spores nearly returned to the initial number after 22 days of hyphal growth. The average relative DNA content in the nuclei of d ormant spores and in the nuclei of spores incubated for 22 days was co mparable, as judged from fluorescence intensity, Hyphal elongation occ urred with 460 nuclei per cm under a special set of in vitro condition s that promote extensive hyphal growth of arbuscular mycorrhizal fungi . We found an average total of 26 000 hyphal nuclei per germinating sp ore after 22 days. The specific DNA polymerase alpha inhibitor aphidic olin did not inhibit spore germination but it rapidly reduced the rate of hyphal growth and arrested growth after 4 days. No nuclei were pro duced de novo during this time. These results demonstrate that G. marg arita replicates nuclear DNA and undergoes nuclear division when grown in vitro even in the absence of a plant host.