RT Journal Article SR Electronic T1 Phytochromes and Cryptochromes in the Entrainment of the Arabidopsis Circadian Clock JF Science JO Science FD American Association for the Advancement of Science SP 1488 OP 1490 DO 10.1126/science.282.5393.1488 VO 282 IS 5393 A1 Somers, David E. A1 Devlin, Paul F. A1 Kay, Steve A. YR 1998 UL http://science.sciencemag.org/content/282/5393/1488.abstract AB 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.