DAPI-DNA staining of cytological sections for rosette leaves. (A-C) First rosette leaf from a 9-day-old plant. (D-F) First rosette leaf from a 31-day-old plant. (G-I) Senescent rosette leaf from a 45-day-old plant. Leaves were sectioned by hand and immediately fixed with glutaraldehyde. Chlorophyll autofluorescence (A, D, G), DAPI-DNA staining (B, E, H), and merged images (C, F, I) are shown. These images are representative of 9–10 microscopic fields from mid-leaf sections of the leaves. Images of autofluorescence and DAPI-DNA staining were recorded at the same exposure times for all samples. The large circular and elliptical intensely DAPI-stained objects correspond to nuclei. The DNA content in mitochondria is much less than in plastids for Arabidopsis , so it is likely that none of the DAPI staining in these images corresponds to mitochondria. White bar in (I), 10 μm, applies to all panels. White arrows indicate chloroplasts that have been magnified 2.9-fold and displayed in the insets shown in the bottom right corners of B, C and E, F.