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.

Cytophotometric Measurement of Nuclear Dna in Seven Heterothallic Isolates of Didymium Iridis, a Myxomycete

“…Therefore, myxamoebae are typically in the G 2 phase of the mitotic interphase, with the G 1 phase being very brief or totally absent. An extended G~phase, resulting in a population of haploid cells predominantly in class 2C has been reported elsewhere (Therrien, 1966;Mohberg and Rusch, 1971;Yemma and Therrien, 1972). The mean DNA content of the plasmodial nuclei is in all cases in category 4C.…”

“…Data are presented as frequency histograms, with the number of nuclei on the ordinate and the DNA content on the abscissa. In this investigation a relative DNA content of 0.32 is equivalent to approximately 0.2 pg of DNA (Therrien, 1966). Swift's (1950) designations, C, 2C, 4C, are used to describe nuclear DNA content.…”

Nuclear Dna Content of Myxamoebae and Plasmodia in Six Non‐heterothallic Isolates of a Myxomycete, Didymium Iridis

“…IN A RECENT SURVEY of 27 isolates of Didymium iridis (Collins, 1976), it was shown that 11 have mating types and 16 do not. From the data presented, those in the first category are cleary sexual (heterothallic), but among the 16 which can complete their life cycle in single-myxamoeba-derived cultures, it was not determined whether the isolates are sexual (homothallic) or non-sexual (apogamic).…”

“…On the other hand an apogamic isolate would not display alternation of haploid and diploid generations, so the DNA level in both myxamoebal and plasmodial nuclei should be the same. Furthermore, since the characteristic nuclear DNA value for several heterothallic isolates of D. iridis are known Yemma, 1974, 1975;Collins and Therrien, 1976) these were used as a standard against which we compared our new findings.…”

“…It was necessary to modify the procedures somewhat for the California 1 isolate because it sporulates prior to forming a large, vigorous plasmodium and also after it forms one. Spores were first germinated on 2 % plain agar, then the myxamoebae transferred to 10 ml of PBS (Therrien and Yemma, 1975) in sterile 125 ml screw-cap Erlenmeyer flasks. E. coli was added to the PBS with the final concentration of the bacteria adjusted to 10 9/ml.…”