Phytochromes and Cryptochromes in the Entrainment of the Arabidopsis Circadian Clock

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Science  20 Nov 1998:
Vol. 282, Issue 5393, pp. 1488-1490
DOI: 10.1126/science.282.5393.1488

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Circadian clocks are synchronized by environmental cues such as light. Photoreceptor-deficient Arabidopsis thaliana mutants were used to measure the effect of light fluence rate on circadian period in plants. Phytochrome B is the primary high-intensity red light photoreceptor for circadian control, and phytochrome A acts under low-intensity red light. Cryptochrome 1 and phytochrome A both act to transmit low-fluence blue light to the clock. Cryptochrome 1 mediates high-intensity blue light signals for period length control. The presence of cryptochromes in both plants and animals suggests that circadian input pathways have been conserved throughout evolution.

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