title: Chloroplast DNA synthesis during the cell cycle in cultured cells of Nicotiana tabacum: inhibition by nalidixic acid and hydroxyurea.
abstract: The effects of nalidixic acid and hydroxyurea on nuclear and chloroplast DNA formation in cultured cells of Nicotiana tabacum were investigated. At low concentrations (5 and 20 micrograms/ml) nalidixic acid, an inhibitor of DNA gyrase, exhibited a greater inhibitory effect on plastid DNA synthesis than on nuclear DNA formation. Since the plastid genome is a circular double-stranded DNA, this is consistent with the proven involvement of a DNA gyrase in the replication of closed circular duplex DNA genomes in procaryotic cells. At a high concentration of nalidixic acid (50 micrograms/ml), DNA synthesis in both the plastid and nuclear compartment was rapidly inhibited. Removal of the drug from the culture medium led to the resumption of DNA synthesis in 8 h. Hydroxyurea, an inhibitor of ribonucleoside diphosphate reductase, also depresses nuclear as well as plastid DNA formation. Removal of hydroxyurea from the blocked cells leads to a burst of nuclear DNA synthesis, suggesting that the cells had been synchronized at the G1/S boundary. The recovery of plastid DNA synthesis occurs within the same time frame as that of nuclear DNA. However, whereas plastid DNA formation is then maintained at a constant rate, nuclear DNA synthesis reaches a peak and subsequently declines. These results indicate that the synthesis of plastid DNA is independent of the cell cycle events governing nuclear DNA formation in cultured plant cells.
authors.forename: S
authors.initials: S
authors.lastname: Heinhorst
authors.forename: G
authors.initials: G
authors.lastname: Cannon
authors.forename: A
authors.initials: A
authors.lastname: Weissbach
mesh_terms: D002453:Cell Cycle; D002478:Cells, Cultured; D002736:Chloroplasts / Q000378:metabolism*; D004261:DNA Replication / Q000187:drug effects*; D004270:DNA, Circular / Q000096:biosynthesis; D006918:Hydroxyurea / Q000494:pharmacology*; D009268:Nalidixic Acid / Q000494:pharmacology*; D010944:Plants / Q000235:genetics*; D010947:Plants, Toxic; D012262:Ribonucleoside Diphosphate Reductase / Q000378:metabolism; D014026:Nicotiana; D059005:Topoisomerase II Inhibitors
chemical_list: D004270:DNA, Circular; D059005:Topoisomerase II Inhibitors; D009268:Nalidixic Acid; D012262:Ribonucleoside Diphosphate Reductase; D006918:Hydroxyurea