A heteroplasmic state induced by protoplast fusion is a necessary condition for detecting rearrangements in Nicotiana mitochondrial DNA.

Mitochondrial DNA (mtDNA) restriction patterns were studied in mutant, cybrid and somatic hybrid plants regenerated from Nicotiana protoplasts.It has been shown that neither components of the culture media used for protoplast culture and plant regeneration, nor the antibiotics streptomycin and lincomycin used for the mutant selection induced alterations in the mtDNA. No rearrangements were detected in the mtDNA of plants derived from homoplasmic fusions where the mtDNA of the parents was identical as judged by mtDNA restriction patterns.There were rearrangements, however, in the mtDNA of each of the cybrid plants derived from heteroplasmic fusions. Restriction patterns generated by BamHI and SalI restriction endonucleases were different from those of both parents, and were composed of parental and non-parental fragments.