DNA Copy Number and Localization, Plastid Genome, Intermolecular Recombination, Flipping, Single Copy Region, Natural Leaf cell

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	DNA Copy Number and Localization - Multiple copies of the plastid genome are found in each cell and in each plastid as well. The amount of DNA per plastid varies with the stage of leaf and chloroplast development. Proplastids with as few as 22 copies of DNA have been reported, whereas chloroplasts in general contain 200 to 300 DNA molecules. The polyploid nature of the plastid genome is even more striking when one considers leaf cells.
In pea, barley and spinach each natural leaf cell contains 9,000 to 13,000 copies of plastid DNA dispersed in 40 to 120 plastids. The very high effective ploidy of the chloroplast genome means that a significant fraction of the total DNA in a cell as much as 30% if the nuclear genome is small may be of chloroplast origin. This means that rbcL, a single copy plastid gene which encodes the large subunit of Rubisco, is present in about 10,000 copies in a mesophyll cell.