MICROSPECTROPHOTOMETRIC MEASUREMENT OF NUCLEAR DEOXYRIBONUCLEIC ACID CONTENT IN TWO MYXOMYCETES

Abstract

Spore formation in Didymium iridis (Ditmar) Fries and Didymium nigripes (Link) Fries is generally preceded by both divisions of meiosis in the developing sporangium, and at the time of cleavage the spores are haploid with the 1C deoxyribonucleic acid (DNA) content. Synthesis of DNA begins soon after spore delimitation and the mature spores are in the haploid 2C category.The plasmodial nuclei were found to have twice the DNA content of the myxamoebae and the mature spores, hence karyogamy must precede plasmodial formation. The myxamoebal and plasmodial nuclei appear to have a very rapid rate of DNA synthesis, with an extended G2 phase of development; consequently myxamoebae are generally in the haploid 2C category and the plasmodial nuclei in the diploid 4C category.In D. iridis the opposite mating types have different amounts of nuclear DNA, and the arithmetical sum of the mean DNA content of the mating types is equal to the mean DNA content of the plasmodial nuclei.In D. nigripes grown on a medium containing 2% w/v glucose a large percentage of uninucleate amoeboid cells have a DNA content equal to that of the plasmodial nuclei. These cells are presumed to be zygotes.