Cytoplasmic male sterility in rapeseed (Brassica napus L.) : 2. The role of a mitochondrial plasmid.

The linear mitochondrial (mt) plasmid in rapeseed occurs in normal, fertile plants, cytoplasmic male sterile (cms) lines (sterile and restored) and maintainers. To determine the role of plasmid genes in cytoplasmic male sterility the three internal Hind III fragments (78%) of the 11.3 kb plasmid were cloned, nick-translated and hybridized to electrophoretic blots of Pst I digests of chloroplast (cp) and mt DNA from normal and cms lines. There is no homology between plasmid DNA and the cp and mt genomes in any line examined nor do plasmid sequences appear to be directly involved in certain alterations of the mt genome. As well, loss of the free plasmid is not associated with integration of the plasmid DNA into the cp or mt genomes. Finally, plasmid copy number appears to be affected by nuclear genotype.