Fig. 2. Mitochondrial uptake of different DNA substrates. (A) Single-strand DNA is not taken up by plant mitochondria. The labeled linear maize 2.3 kb plasmid was incubated in its native form (Nat) or heat- denatured form (Denat) in the presence of potato mitochondria (Imp). Incubation time for uptake was 30 min. Aliquots of the initial native or denatured DNA probe were also loaded on the gel (Cont), showing the migration of the double-strand (ds2.3PL) or single-strand (ss2.3PL) plasmid. The migration shift of the incorporated DNA versus the initial probe was due to the presence of the bulk of the mitochondrial nucleic acids, as shown by mixing a probe aliquot with a nucleic acid sample obtained from an import assay run without substrate. (B) DNA uptake is not sequence specific. Labeled linear DNA corresponding to the pBluescript vector (BLSc), the A.thaliana threonyl-tRNA synthetase (ThrRS), the maize 2.3 kb plasmid cloned in pBluescript (BLSc 2.3PL), as well as labeled circular pBluescript DNA (BLSc circ), were incubated in the presence of potato mitochondria (Imp). Incubation time for uptake was 30 min. Aliquots of the initial DNA probes were also loaded on the gel (Cont). The size and migration of the probes are indicated.