THE STRUCTURE OF MITOCHONDRIAL-DNA FROM THE LIVERWORT, MARCHANTIA-POLYMORPHA

The structure of mitochondrial DNA (mtDNA) from cultured cells of the liverwort, Marchantia polymorpha, was analyzed by pulsed-field gel ele ctrophoresis (PFGE) and moving pictures of the fluorescently labeled m olecules. Previous electron microscopic analysis with this liverwort r evealed a unique property among land plants: mtDNA circles of only one size, that of the 186 kb genome, with no subgenomic circles. Most of the mtDNA was immobile in PFGE and contained complex structures, large r than the genome size with a bright fluorescent node and multiple att ached fibers. The mobile mtDNA was mostly linear molecules in monomeri c to pentameric lengths of the unit genome that increased following mu ng bean nuclease digestion, with a corresponding decrease in the immob ile fraction. From 0 to 5% of the mtDNA was found as circular molecule s the size of the genome and its oligomers; no subgenome-sized circles were present. Radiolabeling revealed that mtDNA synthesis began soon after transfer of cells to fresh medium and most newly replicated mtDN A was immobile; the circular form of the genome was not rapidly labele d. (C) 1998 Academic Press Limited.