title: Action spectrum for cryptochrome-dependent hypocotyl growth inhibition in Arabidopsis.
abstract: Cryptochrome blue-light photoreceptors are found in both plants and animals and have been implicated in numerous developmental and circadian signaling pathways. Nevertheless, no action spectrum for a physiological response shown to be entirely under the control of cryptochrome has been reported. In this work, an action spectrum was determined in vivo for a cryptochrome-mediated high-irradiance response, the blue-light-dependent inhibition of hypocotyl elongation in Arabidopsis. Comparison of growth of wild-type, cry1cry2 cryptochrome-deficient double mutants, and cryptochrome-overexpressing seedlings demonstrated that responsivity to monochromatic light sources within the range of 390 to 530 nm results from the activity of cryptochrome with no other photoreceptor having a significant primary role at the fluence range tested. In both green- and norflurazon-treated (chlorophyll-deficient) seedlings, cryptochrome activity is fairly uniform throughout its range of maximal response (390-480 nm), with no sharply defined peak at 450 nm; however, activity at longer wavelengths was disproportionately enhanced in CRY1-overexpressing seedlings as compared with wild type. The action spectrum does not correlate well with the absorption spectra either of purified recombinant cryptochrome photoreceptor or to that of a second class of blue-light photoreceptor, phototropin (PHOT1 and PHOT2). Photoreceptor concentration as determined by western-blot analysis showed a greater stability of CRY2 protein under the monochromatic light conditions used in this study as compared with broad band blue light, suggesting a complex mechanism of photoreceptor activation. The possible role of additional photoreceptors (in particular phytochrome A) in cryptochrome responses is discussed.
authors.affiliation: Universite Paris VI, Tour 53 E 5, Casier 156, 4, Place Jussieu, 75252 Paris cedex 05, France. ahmad@ccr.jussieu.fr
authors.forename: Margaret
authors.initials: M
authors.lastname: Ahmad
authors.forename: Nicholas
authors.initials: N
authors.lastname: Grancher
authors.forename: Mary
authors.initials: M
authors.lastname: Heil
authors.forename: Robert C
authors.initials: RC
authors.lastname: Black
authors.forename: Baldissera
authors.initials: B
authors.lastname: Giovani
authors.forename: Paul
authors.initials: P
authors.lastname: Galland
authors.forename: Danielle
authors.initials: D
authors.lastname: Lardemer
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000254:growth & development* / Q000528:radiation effects; D029681:Arabidopsis Proteins; D001683:Biological Clocks / Q000502:physiology; D015153:Blotting, Western; D002455:Cell Division / Q000187:drug effects / Q000528:radiation effects; D002940:Circadian Rhythm / Q000502:physiology; D056931:Cryptochromes; D003624:Darkness; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins / Q000235:genetics / Q000378:metabolism*; D018546:Hypocotyl / Q000187:drug effects / Q000254:growth & development* / Q000528:radiation effects; D008027:Light; D009154:Mutation; D017956:Photoreceptor Cells, Invertebrate; D010834:Phytochrome / Q000378:metabolism; D051942:Phytochrome A; D011724:Pyridazines / Q000494:pharmacology; D043562:Receptors, G-Protein-Coupled; D015398:Signal Transduction / Q000502:physiology; D013053:Spectrophotometry / Q000379:methods
chemical_list: D029681:Arabidopsis Proteins; C538962:CRY1 protein, Arabidopsis; D056931:Cryptochromes; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins; C497973:PHYA protein, Arabidopsis; D051942:Phytochrome A; D011724:Pyridazines; D043562:Receptors, G-Protein-Coupled; C119828:cry protein, Drosophila; D010834:Phytochrome; C008677:norflurazone