Sporangia from haploid plasmodia generate spores with low fertility, and it is assumed that viable spores develop from meiosis of rare diploid nuclei in the otherwise haploid P.
This enables easier genetic analysis of plasmodial traits that would otherwise require backcrossing to achieve homozygosity for analysis of recessive mutations in diploids. polycephalum plasmodia can occur without the fusion of amoebae, resulting in haploid plasmodia that are morphologically indistinguishable from the more typical diploid form. In laboratory strains carrying a mutation at the matA mating-type locus, the differentiation of P. The life cycle is completed when haploid amoebae of different mating types fuse to form a diploid zygote that then develops by growth and nuclear division in the absence of cytokinesis into the multinucleate plasmodium. Upon exposure to moist nutrient conditions, the spores develop into amoebae, or, in aqueous suspension, into flagellates. Meiosis occurs during spore development, resulting in haploid dormant spores. When exposed to light, the starving plasmodium differentiates irreversibly into sporangia that are distinguished from other Physarum species by their multiple heads (hence polycephalum). In the dark, the plasmodium typically differentiates reversibly into a dormant “sclerotium” (the same term is used for dormant forms of fungal mycelia, but the myxomycete sclerotium is a very different structure). When the plasmodium is starved, it has two alternative developmental pathways. polycephalum as a model organism to study the cell cycle, or more specifically the nuclear division cycle. When nutrients are provided uniformly, the nuclei in the plasmodium divide synchronously, accounting for the interest in using P. Like amoebae, the plasmodium can consume whole microbes, but also readily grows axenically in liquid cultures, nutrient agar plates and on nutrient-moistened surfaces. While nutrients are available, the network-shaped plasmodium can grow to a foot or more in diameter. The plasmodium is typically diploid and propagates via growth and nuclear division without cytokinesis, resulting in the macroscopic multinucleate syncytium in other words, a large single cell with multiple nuclei. When immersed in water, amoebae differentiate reversibly into flagellated cells, which involves a major reorganization of the cytoskeleton. Under conditions of starvation or desiccation, the amoebae differentiate reversibly into dormant spores with cell walls. Axenic culture of amoebae was achieved through selection of mutants capable of axenic growth. In the laboratory amoebae are grown on lawns of live or dead Escherichia coli on nutrient agar plates, where they can multiply indefinitely. Amoebae are microorganisms, typically haploid, that live primarily in the soil, where they phagocytose bacteria. The two vegetative cell types, amoebae and plasmodia, differ markedly in morphology, physiology and behavior.
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