EVIDENCE OF DNA-REPLICATION IN AN ARBUSCULAR MYCORRHIZAL FUNGUS IN THE ABSENCE OF THE HOST-PLANT

This study provides evidence that Gigaspora margarita replicates its nuclear DNA, even in the absence of a host plant. Three experimental approaches were used: (i) static cytofluorimetry to quantify the DNA content, (ii) pulse treatments with bromodeoxyuridine (BrdU), which is an analogue of thymidine, to reveal nuclei undergoing DNA synthesis, and (iii) ultrastructural observations to study changes in chromatin morphology during the fungal cell cycle. A slight second peak of approximately twice the value of a major peak was found by cytofluorimetry, showing that a small number of nuclei had entered in cycle during in vitro development. Nuclei which had incorporated BrdU were observed after pulses of 24 h; nuclei with condensed chromatin were also apparent at this time. The results demonstrate that G. margarita has all the metabolic pathways needed to replicate its nuclear DNA even in the absence of the host, suggesting that more complex mechanisms inhibit the extended growth in vitro of arbuscular mycorrhizal fungi.