Organelle DNA Synthesis in the Quiescent centre ofArabidopsis thaliana(Col.)

The behaviour of cell nuclei and organelle nucleoids (organelle nuclei) was studied in the root apical meristem of 3-d-old seedlings of Arabidopsis thaliana (Col.). Samples were embedded in Technovit 7100 resin, cut into thin sections and stained with 4′-6-diamidino-2-phenylindole (DAPI) for observation of DNA. DNA synthesis in cell nuclei and organelle nucleoids was investigated using the incorporation of [3H] thymidine or 5-bromo-2′-deoxyuridine (BrdU). Incorporated [3H] thymidine and BrdU were detected by microautoradiography or immunofiuorescence microscopy, respectively. Central cells and cells just above the central cells of the quiescent centre (QC) showed an extremely low activity of DNA synthesis. However, DNA synthesis occurred in at least one organelle nucleoid of all cells in the QC within 24 h. This suggests the cells in the QC are quiescent with regard to nuclear DNA synthesis, but not with regard to the organelle nucleoids.