Net synthesis of chloroplast DNA throughout the synchronized vegetative cell-cycle of Chlamydomonas.

The accumulation of chloroplast and nuclear DNAs during the 12 h light and 12 h dark synchronized vegetative cell-cycle of Chlamydomonas reinhardtii was monitored by the direct optical quantification of these DNAs in the analytical ultracentrifuge. Net synthesis of nuclear DNA was sharply discontinuous and this synthesis occurred during the first 6 h of the dark period. In contrast, the net synthesis of chloroplast DNA appeared continuous throughout the cell-cycle. The rate of this accumulation, however, was greatest in the dark period.