Abstract
Loss of chloroplast DNA and concomitant chloroplast replication were examined in Euglena gracilis Z grown photoheterotrophically in the presence of 50 μg/ml of nalidixic acid (NAL), a potent inhibitor of DNA replication. Staining with DNA-specific sensitive fluorochrome 4', 6-diamidino-2-phenylindole (DAPI) revealed that the Euglena chloroplast contains 30 or more DNA regions (nucleoids) and that NAL induced the loss of chloroplast nucleoids in a large chloroplast population within 2-3 generations after its addition. No chloroplast nucleoids were detectable in 73 % of the chloroplasts isolated from cells treated with NAL for 72 h. Although the chlorophyll content per cell markedly decreased and the chloroplast DNA was depleted, cell divi-sion and chloroplast replication were scarcely inhibited, at least within 96 h after the addition of NAL.
These results show that chloroplast replication is not affected by the inhibi-tion of replication of chloroplast DNA. They also suggest that chloroplasts are able to replicate several times after nucleoids are no longer detectable by the DAPI method.
