Chloroplast replication in synchronously dividing Euglena gracilis

Chloroplast replication was studied in Euglena gracilis Klebs, strain Z, synchronized by appropriate light-dark cycles. The chloroplasts divide synchronously, at the time of cytokinesis, but with a tighter synchrony than cell division itself. The chloroplasts within one cell are not noticeably better synchronized than those in the whole population. Chloroplast replication and cell division could not be separated by resetting the time of the light-dark cycle which induces the synchrony. These results are discussed for their implications concerning the mechanisms of integrating cell and plastid division.