A gene modifying mitochondrial malate dehydrogenase isozymes in Sorghum (Gramineae)

Malate dehydrogenase (MDH) isozymes extracted from dark-grown seedlings of Sorghum species are encoded by at least two genes with their products localized in the mitochondria (mt) and one gene with its products localized in the cytosol. In homozygous genotypes, the three mt-MDH isozymes represent two homodimers and an intergenic heterodimer. For some plants of S. virgatum and S. aethiopicum, the three mt-MDH isozymes migrate about 3 mm faster (more anodally) when electrophoresed on starch gels. The F1's of plants with normal and fast mt-MDHs had normal migration; the F2's segregate 3:1 for normal to fast migration. It is suggested that a single gene, Mmm (mt-MDH modifier), controls this modification of normal migration and that fast migration occurs when the recessive allele (mmm-m) is homozygous. The designation, Mmm, is borrowed from Zea mays, in which a similar gene has been described.