PHYTOCHROMES AND CRYPTOCHROMES IN THE ENTRAINMENT OF THE ARABIDOPSIS CIRCADIAN CLOCK

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