Amoebae Of Physarum Polycephalum Research Articles

Viability of Physarum polycephalum spores and ploidy of plasmodial nuclei.

Amoebae of Physarum polycephalum carrying the mth mating-type allele may differentiate into plasmodia in the absence of mating. Such plasmodia are haploid and, upon sporulation, produce mainly inviable spores. We have asked whether the viable spores arise from meiotic or mitotic divisions. Using a microfluorometric measurement of the deoxyribonucleic acid content of individual nuclei, we found the fraction of viable spores to be correlated with the proportion of rare, diploid nuclei containing in the generally haploid plasmodium. When homozygous diploid plasmodia were created by heat shocking, spore viability increased dramatically. We suggest that viable spores are produced via meiosis in mth plasmodia, that the mth allele has no effect on sporulation per se, and that the normal source of viable haploid spores is a small fraction of diploid nuclei ubiquitous in haploid plasmodia.

Defined and semi-defined media for the growth of amoebae of Physarum polycephalum.

Amoebae of the true slime mould Physarum polycephalum were cultured in two fully-defined liquid media containing amino acids, glucose, three vitamins and a buffered salts solution. Absolute requirements were demonstrated for methionine, haematin, thiamine and biotin, all of which were known to be specific requirements of the plasmodial stage. Methods are described for large-scale culture in three semi-defined media.

The amoebal cell of Physarum polycephalum: Colony formation and growth

Two stages of colony growth were observed during microscopic studies of Physarum polycephalum amoebae. During the first stage, “spreading growth,” the colony is composed of dispersed single cells. During the second stage, “aggregate growth,” most of the active cells in a colony are aggregated in a ring at the colony boundary. Measurements of cell movement as a function of bacterial concentration indicate that, during both spreading and aggregate growth, cell movements are not affected by changes in bacterial concentration but that the transition from spreading to aggregate growth occurs earlier on plates with lower bacterial concentrations. These results indicate that autonomous characteristics of the amoebae are more important for the determination of colony form than local variations in the concentrations of nutrients. The genetic determination of colony form is demonstrated by the existence of mutants that display specific alterations in colony morphology. Because the aggregate rings of these mutants move at an increased rate, mutant clones appear as variant sectors of wild-type colonies. The increased rate of mutant ring movement suggests that this selection method may be a useful technique for isolating mutant myxamoebae with defects in movement and behavior.