A gene conferring actidione resistance and abnormal morphology onPhysarum polycephalumplasmodia

SUMMARY Plasmodia of P. polycephalum homozygous and heterozygous for a mutation ( act ) which confers resistance to actidione on the haploid amoebal stage have been tested for resistance to actidione in liquid semidefined medium. Growth of homozygous resistant ( act/act ) plasmodia determined by protein or pigment assay was inhibited less by actidione than growth of homozygous-sensitive or heterozygous plasmodia. The mutant ( act ) is therefore recessive but, contrary to a previous report, confers resistance on homozygous plasmodia. The same mutation affects the morphology of homozygous ( act/act ) plasmodia on agar medium, causing slow growth, fragmentation and excessive sliminess.