Organelle DNA Synthesis before Cell Nuclear Replication is Essential for Subsequent Cell Propagation

Abstract

Elevation of intra-cellular organelle DNA levels due to preferential synthesis of organelle DNAs before cell multiplication is generally observed in meristematic cells of higher plants, such as those in apical meristems and cultured cells. We analyzed the physiological significance of this phenomena using cultured tobacco cell BY-2 as a model system for cell multiplication in plants. Cultured tobacco cell BY-2 multiplied approximately 50-fold in a week in normal culture medium. However, when nalidixic acid, which inhibits prokaryotic DNA gyrase, was added to the culture, synthesis of organelle DNA was selectively inhibited and cell multiplication was arrested. This indicates that the synthesis of organelle DNAs is a prerequisite for cell multiplication. To quantitatively clarify the effect of the elevation of organelle DNA levels on the capacity for cell proliferation, cells with various organelle DNA levels were prepared by preculturing cells for various lengths of time in culture medium which contained aphidicolin, a specific inhibitor of eukaryotic DNA polymerase a, and then transferring them to culture medium which contained nalidixic acid. Their growth rates in the absence of further organelle DNA synthesis were monitored. A correlation was observed between intra-cellular organelle DNA levels and the capacity of the cells to proliferate, indicating that intra-cellular organelle DNA levels limited the capacity for cell proliferation.