Mitochondrial nature of newly synthesized DNA in aging coleoptiles of etiolated wheat shoots

: In mature ageing coleoptiles as well as in cut-off etiolated wheat shoots exhausted by incubation in H2O nuclear DNA (nDNA) synthesis does not occur. However, the synthesis of another DNA is continued under these conditions. The parameters of this DNA (e. g. buoyant density, rho = 1.716 g/cm3, and composition - 56 mol.% GC) differs from those of nDNA (rho = 1.700 g/cm3, 44 mol.% GC). The newly synthesized DNA is non-methylated and metabolically stable. It is not sensitive to cycloheximide (20 micrograms/ml) but is markedly inhibited by ethidium bromide (2-10 micrograms/ml). The synthesis of this DNA is localized in the mitochondria, thus indicating that in ageing coleoptiles and exhausted wheat shoots all the newly synthesized DNA is of mitochondrial origin.