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After incubation of etiolated wheat seedlings in the presence of [8‐14C]adenine the radioactive N 6‐methyladenine (m6A) has been detected in the newly synthesized mitochondrial DNA (mtDNA) (ML = 100·m6A/(m6A+A)=0.4–0.6). This DNA is a low molecular mass (7.7 S) fraction of the mtDNA population. The detection of N 6‐methyladenine in the mtDNA of wheat seedlings indicates the presence of adenine DNA methylase in mitochondria of higher plants. The presence of m6A in plant mtDNAs makes them distinct from animal mtDNAs in which, as we know, this additional base has not been found.

On incubation of 7‐day‐old wheat seedlings in the presence of [3H]thymidine, the radioactivity incorporated into coleoptile DNA is found to be localized mainly (>95%) in the fraction of heavy mitochondrial DNA (H‐mt DNA: ϱ = 1.716 gm/cm3). Upon long (48–72 h) incubation of cut‐off seedlings in water, the amount of this DNA shows a dramatic increase corresponds to about 10% of the total coleoptile DNA. H‐mtDNA is represented by open circular molecules with a contour length varying from 0.12 to 0.6μm. The functional role of this DNA is still unknown.

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