Photocycle and signaling mechanisms of plant cryptochromes

Cryptochromes are flavoprotein blue light receptors that control many aspects of plant growth and development including seedling de-etiolation, elongation growth, the initiation of flowering, and entrainment of the circadian clock. Photon absorption by Arabidopsis cryptochromes cry1 and cry2 initiates electron transfer to the oxidized flavin cofactor (FADox) and formation of the presumed biological signaling state FADH°. Current literature on the nature and formation of the signaling state is reviewed, and potential novel roles for cryptochromes in oxidative stress and as magnetosensors are discussed in light of the cryptochrome photocycle.