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.
