XVI International Botanical Congess

Each wild type Chlamydomonas cell has one large chloroplast (cp) containing several cp-nucleoids. We have isolated Chlamydomonas mutants that contain a single, large cp-nucleoid by DNA insertional mutagenesis. We named these mutants moc (monokaryotic chloroplast). DAPI-fluorescence microscopy and microphotometry observations revealed that moc mutant cells only contain one cp-nucleoid throughout the cell division cycle, and that unequal segregation of cpDNA occurred during cp-division. Electron microscopic observation showed that a low-electron density area, which was identified as the cp-nucleus by immunoelectron microscopy using anti-DNA antibody, existed near the pyrenoid. We propose that the novel moc mutants are defective in the dispersion and segregation of cpDNA.