Comparison of the structural forms of cpDNA molecules from different tissues. EtBr-stained cpDNA from young (A, D, G; 9-day-old first and second rosette leaves), intermediate (B, E, H; entire 20-day-old shoots), and mature (C, F, I; third rosette leaf of a 31-day-old plant) was visualized by fluorescence microscopy and characterized by structural class. (A-C) Class I structures: complex forms consisting of a network of connected fibers or fibers connected to a large, dense core. (D-F) Class II structures: complex forms with a greater number of disconnected fibers than connected fibers. (G-I) Class III structures: disconnected fibers without a complex form. Values at the bottom left corner represent the number of molecules in a particular structural class out of the total number of structures observed for each tissue. The scale bar shown in (I) applies to all images.