HEAVY MITOCHONDRIAL-DNA IN HIGHER-PLANTS

Synthesis of a heavy (rho = 1.713-1.729 g/cm3) fraction of mitochondrial DNA (H-mtDNA) in the absence Of synthesis of nuclear DNA has been found in all studied plant species from various taxonomic groups of archegoniates (Bryophyta, Pteridophyta, and Gymnospermae) and angiosperms (Monocots and Dicots). The synthesis of H-mtDNA is inhibited by ethidium bromide. H-mtDNA is the main fraction (greater-than-or-equal-to 90%) of the total newly synthesized DNA in differentiated cells of plant organs. The buoyant densities of H-mtDNAs in CsCl density gradients area 0.012-0.031 g/cm3 higher than those of nuclear DNAs. H-mtDNA of all higher plants studied contain N6-methyladenine [ML(A) = 100.m6A/(m6A + A) = 0.3-1.0] but not 5-methylcytosine residues. The biological functions of H-mtDNA in plants are unknown.