Modification Of Mitochondrial DNA Research Articles

Mitochondrial DNA modifications associated with cytoplasmic male sterility in rice

Mitochondrial DNA was isolated from fertile and cytoplasmic male sterile lines of rice. Restriction analysis showed specific modifications in the male sterile cytoplasm. In addition to the major mitochondrial DNA, three small plasmid-like DNA molecules were detected by agarose gel electrophoresis in both cytoplasms. An additional molecule was specifically found in the sterile cytoplasm. These mitochondrial DNA modifications support the hypothesis of the mitochondrial inheritance of the cytoplasmic male sterility in rice.

Effects of mutagenic treatment by ethidium bromide on cellular and mitochondrial phenotype

The phenotypic consequences of quantitative mutagenesis by ethidium bromide (EB) have been investigated. When starved cells (2 × 10 7/ml in phosphate buffer) of Saccharomyces cerevisiae are treated with 20 μg EB/ml for 150 min, they generate respiration deficient cytoplasmic petite ( p −) clones to the extent of greater than 98%. Phenotypically such a population of EB-induced cells (EBIC) growing in the absence of the mutagen is initially respiration sufficient but loses its capability of growth on a nonfermentable carbon source (e.g., lactate) within 2–3 mass doublings. In contrast EBIC are capable of continued and sustained growth on galactose, a fermentable but weakly repressing carbon source. Under all these conditions the initial phenotypic lesion appears to be confined to the inner mitochondrial membrane and is manifested by an inability of elaborating cytochrome oxidase activity and cytochromes a· a 3 + . These results are explained in terms of an EB-induced modification of mitochondrial DNA which makes impossible the continued transcription of a gene product(s) essential for the functions just described.