INVESTIGATION OF PLANT ORGANELLAR DNAS BY PULSED-FIELD GEL-ELECTROPHORESIS

Mitochondrial (mt) DNAs from several higher-plant species (Arabidopsis thaliana, Beta vulgaris, Brassica hirta, Chenopodium album, Oenothera berteriana, Zea mays) were separated by pulsed-field gel electrophore sis (PFGE). Hybridization of the separated DNA with mtDNA-specific pro bes revealed an identical distribution of mtDNA sequences in all cases : part of the DNA formed a smear of linear molecules migrating into th e gel, the rest remained in the well. Hybridization signals in the com pression zone of the gels disappeared after RNase or alkaline treatmen t. It was shown that the linear molecules are not products of unspecif ic degradation by nucleases. All plastid (pt) DNA from leaves of Nicot iana tabacum remained in the well after PFGE. Separation of linear mon omers and oligomers of the chloroplast chromosomes of N. tabacum was a chieved by mild DNase treatment of the well-bound DNA. DNase treatment of well-bound mtDNA, however, generated a smear of linear molecules. PtDNA from cultured cells of C. album was found after PFGE to be partl y well-bound, and partly separated into linear molecules with sizes of monomeric and oligomeric chromosomes. The ease with which it was poss ible to detect large linear molecules of plastid DNA indicates that sh earing forces alone can not explain the smear of linear molecules obta ined after PFGE of mtDNA. The results are discussed in relation to the structural organization of the mt genome of higher plants.