HEAVY MITOCHONDRIAL-DNA IN HIGHER-PLANTS

Synthesis of a heavy (rho = 1.713-1.729 g/cm3) fraction of mitochondri al DNA (H-mtDNA) in the absence Of synthesis of nuclear DNA has been f ound in all studied plant species from various taxonomic groups of arc hegoniates (Bryophyta, Pteridophyta, and Gymnospermae) and angiosperms (Monocots and Dicots). The synthesis of H-mtDNA is inhibited by ethid ium 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 a rea 0.012-0.031 g/cm3 higher than those of nuclear DNAs. H-mtDNA of al l higher plants studied contain N6-methyladenine [ML(A) = 100.m6A/(m6A + A) = 0.3-1.0] but not 5-methylcytosine residues. The biological fun ctions of H-mtDNA in plants are unknown.