| dc.description |
Two types of clocks, i.e., the circadian oscillator and the hourglass mechanism, which under continuous light and darkness respectively control the mutually inverse temporal changes in the activities of Cyt-NAD-GPD and Chl-NADP-GPD of Lemna gibba G3, were studied. Both clocks controlled the apparent Km values, not the Vmax values, of the GPD reactions for their substrate and coenzymes. A red light pulse inserted 3 hr after the onset of the dark period eliminated the sigmoidal changes in darkness, but evoked rhythmical changes which otherwise did not occur in continuous darkness. Thus, the photosynthetic rhythm, if present, would not sustain the GPD rhythms. This effect of a red light pulse was not nullified by a subsequent far red light pulse. A far red light pulse given at the 3rd hour of an extended dark period made conspicuous the sigmoidal changes in activity of GPDs in the dark period, and its effect was nullified by a subsequent red light pulse, suggesting that phytochrome is involved in the hourglass mechanism. |
