Variable abundance of a mitochondrial DNA fragment in cultured tobacco cells

The relative abundance of a cloned 4.5 kilobase (kb) pair mitochondrial DNA sequence in two suspension cultures of tobacco (Nicotiana tabacum cv Turkish samsun and Nicotiana tabacum NT-1) has been examined. This sequence is 70-fold reduced in NT-1 relative to Turkish samsun; the reduction is correlated with an increase in supercoiled mitochondrial DNA. This sequence does not hybridize with mitochondrial DNA from watermelon, maize, or Saccharomyces cerevisiae, nor with several cloned mitochondrial genes and is thus probably not a gene. It may represent most of the plant mitochondrial genome thought to be non-essential for mitochondrial function. The sequence complexity of supercoiled mitochondrial DNA from NT-1 cells is about one-third that found for the entire mitochondrial genome and does not include the cytochrome oxidase subunit II gene.