COMPARATIVE MEASUREMENTS OF NUCLEAR DNA IN A HETEROTHALLIC AND A SELF‐FERTILE ISOLATE OF THE MYXOMYCETE, DIDYMIUM IRIDIS

Abstract

Comparative measurements were made of the nuclear Feulgen‐DNA content of a heterothallic and a self‐fertile isolate of the myxomycete Didymium iridis. Plasmodial nuclei of both isolates contain the diploid amount of DNA. The replicated diploid (4C) values for the heterothallic and the self‐fertile isolates are 5.66 and 5.95, respectively. Myxamoebae, however, are quite dissimilar in their nuclear DNA content. Those of the heterothallic isolates, Honduran 1–2 (A1) and Panamanian 2–4 (A7), have mean values of 3.81 and 3.69, whereas myxamoebae of the self‐fertile Philippine‐1 isolate were found to have a mean value of 6.07. Myxamoebae of the Ph‐1 isolate are, therefore, at the same ploidy level as the Ph‐1 Plasmodium. Mean DNA values for Ph‐1 sporangial nuclei were in category 4C. Measurement of the DNA content of mitotic metaphases in sporangia at T = 6 hr confirmed that the mean DNA content of both Ph‐1 myxamoebae and plasmodial nuclei is equivalent to 4C. It is concluded that nuclear phase alternance is lacking in the Ph‐1 isolate and that the Plasmodium of this isolate develops by apogamy.