The mitochondrial genome of higher plants : mtiochondrial DNA, cytoplasmic male sterility, S cytoplasm
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Mitochondrial (mt) DNAs of higher plants have molecular weights ranging from 70-165 x 10 [superscript 6], which is by far the largest found in nature. Their native configuration is probably a covalently closed circular molecule. In some species, the entire mt genome is coded on a single molecule but in others several classes of mtDNA molecules have been indicated. The informational content of the mt genome of higher plants is poorly determined. The large size predicts that additional information is coded by these mt genomes. Evidence is presented which suggests that cytoplasmic male sterility (cms) is one of the additional traits. Sequence differences have been detected among mt DNAs isolated from plants from different cytoplasmic backgrounds. Although the sequence distinctions are of unknown consequence, it is important because it establishes that diversity exists among mt genomes within a species. Associated with mitochondria from the S cytoplasm of maize are two unique plasmid-like DNAs. Seemingly, these unique DNAs are responsible for the S type of cms as well as the unstable behavior of this cytoplasm.