Inheritance of plasmodial valine requirement inPhysarum polycephalum

Abstract

SUMMARYA defined medium forPhysarum polycephalumplasmodia has been devised containing glutamic acid, glycine, methionine, biotin, thiamine, glucose, salts and haematin, which supports good growth on agar plates of many different strains. Tests on this medium have revealed a requirement for valine in some plasmodia formed by homothallic progeny (mthapt-l+) from the crossa(mt1apt-l+) ×APT1(mthapt-l−). The valine requirement was also inherited among heterothallic progeny of this cross and its segregation was followed in several heterothallic crosses. To explain the results it is proposed that valine synthesis requires the presence of dominant alleles at either of two unlinked loci and that only plasmodia homozygous for recessive alleles at both loci are valine dependent. In some crosses studied only one pair of alleles is segregating and valine requirement thus provides a useful genetic marker, and the first reported nutritional marker inP. polycephalum. The value of crosses withapt−mutants for both the detection and analysis of plasmodial markers is demonstrated and discussed.