Viability of Physarum polycephalum spores and ploidy of plasmodial nuclei

Area of Science:

• Cell Biology
• Mycology
• Genetics

Background:

• The slime mold Physarum polycephalum, when carrying the mth mating-type allele, can form plasmodia without mating.
• These haploid plasmodia typically produce mostly inviable spores upon sporulation.

Purpose of the Study:

• To investigate the origin of viable spores from haploid P. polycephalum plasmodia.
• To determine if viable spores result from meiotic or mitotic divisions.

Main Methods:

• Microfluorometric measurement of DNA content in individual nuclei.
• Induction of homozygous diploid plasmodia via heat shock.

Main Results:

• A correlation was observed between viable spore fraction and the proportion of rare diploid nuclei within haploid plasmodia.
• Heat-shock-induced homozygous diploid plasmodia exhibited a dramatic increase in spore viability.

Conclusions:

• Viable spores in mth plasmodia are likely produced through meiosis.
• The mth allele does not inherently affect sporulation; diploidy is crucial.
• A small, ubiquitous population of diploid nuclei in haploid plasmodia is the primary source of viable haploid spores.