Plasmodium formation without change in nuclear DNA content inPhysarum polycephalum

Abstract

The Colonia isolate of Physarum polycephalum produces plasmodia within amoebal clones. Wheals demonstrated genetically that amoebae of the C50 strain of this isolate, when crossed with heterothallic amoebae, yielded recombinant progeny. He concluded that nuclear fusion and meiosis occurred in these crosses and suggested that nuclear fusion was also involved in plasmodia formation in clones. He thus designated the strain 'homothallic'.In the present work genetic evidence is presented which indicates that the Colonia strain CL, when crossed with heterothallic strains, also yields recombinant progeny and thus undergoes nuclear fusion and meiosis. Microdensitometric measurements of nuclear DNA content are reported which indicate that CL amoebae are haploid like heterothallic amoebae, and crossed plasmodia are diploid. However, clonally formed CL plasmodia were found to have the same G 2 nuclear DNA content as CL amoebae. This observation excludes the possibility of nuclear fusion when plasmodia form within clones of CL amoebae and therefore the strain cannot be homothallic. Two alternatives, apogamy and coalescence, are proposed as the most likely mechanisms for clonal plasmodium formation in strain CL.

Pyrimidine Metabolism in Microplasmodia of Physarum polycephalum

“…The strain CL has recently been shown to be haploid in both the amoeba1 and plasmodia1 stages of the life cycle [9]. Stock cultures were kept in standard semi-defined …”

Non-synchronous Degradation of Centrioles during Mating in Physarum polycephalum.

“…This is accompanied by the loss of centrioles, which also results in the loss of amoebo-flagellate transformation. There are some mutant strains which omit several of these mating steps, i.e., cell fusion, karyogamy and formation of diploid cell nuclei, by forming plasmodia directly from a single amoeba genotype (Anderson et al 1976, Cooke andDee 1974). This phenomenon is known as amoebal-plasmodial transition as opposed to plasmodium formation through mating.…”

Plasmodium development in the myxomycete Physarum polycephalum: genetic control and cellular events

“…The third mating-type gene, m a t A (Dee, 1960, has no effect on amoebal fusion but controls subsequent development of the fusion cell (Youngman e t al., 1981). When two amoebae carrying the same matA allele fuse, development is blocked before nuclear fusion.…”