Genetic flexibility of plant chloroplasts

The chloroplast genome is thought to be monomorphic, or genetically uniform within individual plants 1 . But a single plant cell may contain several hundred chloroplasts, each containing up to 900 copies of DNA 2 , so there is a huge potential for accumulating and maintaining mutations. I found that the chloroplast genome of common groundsel, Senecio vulgaris ,is polymorphic for a point mutation that confers resistance to triazine herbicides.Moreover, this polymorphism can vary within and among different leaves of a single plant.