Heterogeneity of circular mitochondrial DNA molecules from sugar beet with normal and male sterile cytoplasms.

Mitochondrial (mt) DNAs from normal (N) and male sterile (S) cytoplasms of sugar beet have been isolated and investigated by electron microscopy. The results showed that mtDNA was composed of a heterogeneous population of circular molecules. Their contour lengths varied from 0.28 to 51 micron, but unlike in the case of maize, a large difference was not observed in the distribution of molecular classes greater than 1.0 micron between N and S cytoplasms of sugar beet. On the other hand, N and S cytoplasms were shown to contain their own characteristic combinations of small circular mtDNA species with lengths between 0.28 micron and 0.6 micron. Mitochondrial DNAs from various sources of male-sterile cytoplasms were analyzed by agarose gel electrophoresis to determine the extent of cytoplasmic variation. Additional low molecular weight DNA bands appeared in all male-sterile lines examined, and as a result, three distinctive banding patterns were recognized. These data are in general agreement with those based upon restriction endonuclease digestion of mt and chloroplast DNAs and the genetic analysis of fertility restoration in test crosses.