The heterogeneous composition of mitochondrial DNA in somatic hybrid calli and the relatively simple composition of such DNA in regenerated leaves

Mitochondrial (mt) and chloroplast (ct) DNA were characterized in somatic hybrids obtained by fusion of protoplasts from two species, Nicotiana glauca and N. langsdorffii. Three and a half months after the fusion, total DNA was extracted from 50-100 mg of callus and of leaf tissue. Southern hybridization was carried out with several probes from organelle DNA. The results revealed that widespread rearrangements of mtDNA had occurred in the majority of hybrid calli. Even subclones derived from the same original hybrid callus generated different patterns of rearrangements. In contrast to our results for calli, we found that leaves contained almost a simple parental-type mtDNA, namely, that of N. langsdorffii in this experiment, and few rearrangements of mtDNA were detected. Data obtained with cob as probe distinctly showed the difference between calli and leaves. These results suggest that there may be a correlation between the organization of mtDNA in hybrids and the ability of hybrids to regenerate, since nuclear genomes of hybrids are known to be stable. Segregation of two kinds of ctDNA was observed more frequently in leaves than in calli. It was also apparent that there was no correlation between species of chloroplasts and species of mitochondria since we found a heterogeneous component of organelles.