Preparation of tomato nuclei for proteomic analysis. (a) Micrographs showing representative nuclear fractions from tomato fruits after 4′,6-diamidino-2-phenylindole (DAPI) staining. The phase-contrast micrograph and the fluorescence micrograph of the nuclei are presented. Scale bar, 25 μm. (b) Western blot analysis of the different purification fractions with antibodies directed against histone H3, UDP-glucose pyrophosphorylase (UGPase), and photosystem II reaction centre protein D1 (PsbA). T, total protein extract; S1, supernatant fraction from centrifugation at 3,000 × g; S2, supernatant fraction after 1% Triton X-100 treatment and centrifugation; S3, supernatant fraction from sucrose density centrifugation; N, nuclear protein extract.