Abstract
Although electron microscopy techniques allow visualization of each individual plastid genome, it is not applicable to observe hundreds or thousands of such molecules at once. We tested YOYO-1, an intercalating fluorescence dye for DNA, for the visualization of individual plastid genomes through a fluorescence microscope. Plastids in leaves of spinach and tobacco were purified by Percoll density gradient centrifugation, and the plastid DNA was prepared by lyses of the plastids on poly-L-lysine coated slides. The YOYO-1 detected a single plastid genome as either a circular or a linear DNA molecule having between 30-40 μm in length. On the other hand, the molecules of more than 100 μm also appeared in low frequency, suggesting that multimeric conformations occurred in a subpopulation of plastid genomes. Visualization of a single gene in plastid genome is being carried out with the fluorescence in situ hybridization technique.
