Photocontrol of Nuclear DNA Replication in Chattonella antiqua (Raphidophyceae)

概要

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The timing of nuclear DNA replication was examined in a synchronized cell population of a red-tide flagellate, Chattonella antiqua, using fluorescence microspectrophotometry with a DNA-specific fluorochrome, 4',6-diamidino-2-phenylindole (DAPI). Under alternating 12-h periods of light and dark (12L12D), nuclear DNA began to increase synchronously ca. 10 h after the onset of light irradiation. Even when the light-off timing of the light period or the whole span of the 12-h light period was shifted after synchronization under 12L12D cycles, the timing of the beginning of nuclear DNA replication was invariably ca. 10 h from the onset of light irradiation. When irradiation was not given, there was no increase of nuclear DNA. The conclusion reached was that light irradiation is necessary for nuclear DNA replication in Chattonella antiqua and that the timing of the replication is dependent upon only the timing of the onset of the last irradiation. In other words, a light-on signal induces the transition of cell nuclei from the G_1 into the S phase and also determines the timing of this event. When not irradiated, cells are arrested in the G_1 phase.
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