Chloroplast DNA of Acetabularia mediterranea: Cell cycle related changes in distribution

Chloroplast DNA (cpDNA) distribution in the giant unicellular, uninucleate alga Acetabularia mediterranea was analyzed with the DNA-specific fluorochrome 4'6-diamidino-2-phenylindole (DAPI) at various stages of the cell cycle. The number of chloroplasts exhibiting DNA/DAPI fluorescence changes during the cell's developmental cycle: (1) all chloroplasts in germlings contain DNA; (2) the number of plastids with DNA declines during polar growth of the vegetative cell; (3) it increases again prior to the transition from the vegetative to the generative phase; (4) several nucleoids of low fluorescence intensity are present in the chloroplasts of the gametes. The temporal distribution of the number of chloroplasts with DNA appears to be linked to the different mode of chloroplast division and growth during the various stages of development. The chloroplast cycle in relation to the cell cycle is discussed.