The blue light receptor cryptochrome 1 can act independently of phytochrome A and B in Arabidopsis thaliana

Blue light responses in higher plants can be mediated not only by specific blue light receptors, but also by the red/far-red photoreversible phytochro me system. The question of interdependence between these photoreceptors has been debated over many years. The availability of Arabidopsis mutants for the blue light receptor CRY1 and for the two major phytochromes phyA and ph yB allows a reinvestigation of this question. The analysis of photocontrol of seed germination, inhibition of hypocotyl growth and anthocyanin accumul ation clearly demonstrates that (i) phyA shows a strong control in blue lig ht responses especially at low fluence rates; (ii) phyB mediated induction reactions can be reversed by subsequent blue light irradiations; and (iii) CRY1 mediates blue light controlled inhibition of hypocotyl growth only at fluence rates higher than 5 mu mol m(-2)s(-1) and independently of phytochr ome A and B.