EVIDENCE FOR A HAPLOID LIFE-CYCLE IN VOLVARIELLA-VOLVACEA FROM MICROSPECTROPHOTOMETRIC MEASUREMENTS AND OBSERVATIONS OF NUCLEAR BEHAVIOR

Fluorescence microspectrophotometric measurements of 4,6'-diamidino-2-phenylindole-stained nuclei at different developmental stages of Volvariella volvacea were made and analysed statistically. A uninucleate spore germinated to a mycelial mat of multinucleate simple-septate hyphae, which aggregated to form fruiting bodies of multinucleate tissues. Nuclei in a hyphal compartment were irregular in shape and size and asynchronous in nuclear phase. A hymenial initial without clamp connection was uninucleate. The hymenium at the button stage was composed of multinucleate cystidia and uni- to hi-nucleate cells, suggesting the insertion of basidia into the hymenium at later stages or arrest of basidial development at this stage. Typical meiotic figures were observed in basidia, and anucleate basidia remained after spore discharge. Together with the measurement made with nuclei of a single spore isolate, the changes in DNA contents provided direct evidence for a haploid life-cycle with the transient diploid stage limited to prophase I, at which meiotic DNA synthesis took place, in basidia of V. volvacea.