Changes in sugar beet mitochondrial DNA induced during callus stage

The organization of mitochondrial DNA was studied in seed-derived plants of sugar beet, Beta vulgaris L., and compared with the structure of DNA isola ted from calli propagated in vitro. Tissues representing three genotypes (d iploid male sterile, diploid maintainer and diploid fertile) were maintaine d under in vitro conditions for different periods before the DNA was analys ed. Restriction fragment length polymorphism with BamHI and XhoI enzymes, a nd Southern hybridization with atpA and atp6 homologous probes were used. H ybridization experiments showed conspicuous differences in the organization of both genes in long-term callus cultures (2 years or older). The novel o rganization of mitochondrial DNA in the calli of the male sterile genotype showed an additional 3.9 kb fragment after hybridization with the atp6, and 7.9 kb and 3.5 kb bands after hybridization with atpA. In the fertile geno type, changes in mitochondrial DNA structure were manifested in the disappe arance of a 2.1 kb fragment after probing with atpA. Alterations induced in the mitochondrial genome of the male sterile line showed unique features i n mtDNA rearrangements.