title: Ultraviolet B radiation enhances a phytochrome-B-mediated photomorphogenic response in Arabidopsis.
abstract: Ultraviolet B radiation (UV-B, 290-315 nm) can cause damage and induce photomorphogenic responses in plants. The mechanisms that mediate the photomorphogenic effects of UV-B are unclear. In etiolated Arabidopsis seedlings, a daily exposure to 2.5 h of UV-B enhanced the cotyledon opening response induced by a subsequent red light (R) pulse. An R pulse alone, 2.5 h of UV-B terminated with a far-red pulse, or 2.5 h of continuous R caused very little cotyledon opening. The enhancing effect of UV-B increased with fluence rate up to approximately 7.58 micromol m(-2) s(-1); at higher fluence rates the response to UV-B was greatly reduced. The phyA, phyA cry1, and cry1 cry2 mutants behaved like the wild type when exposed to UV-B followed by an R pulse. In contrast, phyB, phyB cry1, and phyB phyA mutants failed to open the cotyledons. Thus, phytochrome B was required for the cotyledon opening response to UV-B --> R treatments, whereas phytochrome A and cryptochromes 1 and 2 were not necessary under the conditions of our experiments. The enhancing effect of low doses of UV-B on cotyledon opening in uvr1 uvr2 and uvr1 uvr3 mutants, deficient in DNA repair, was similar to that found in the wild type, suggesting that this effect of UV-B was not elicited by signals derived from UV-B-induced DNA lesions (cyclobutane pyrimidine dimers and 6-4 photoproducts). We conclude that low doses of UV-B, perceived by a receptor system different from phytochromes, cryptochromes, or DNA, enhance a de-etiolation response that is induced by active phytochrome B.
authors.affiliation: Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura, Consejo Nacional de Investigaciones Científicas y Técnicas, Avenida San Martín 4453, C1417 DSE Buenos Aires, Argentina.
authors.forename: H E
authors.initials: HE
authors.lastname: Boccalandro
authors.forename: C A
authors.initials: CA
authors.lastname: Mazza
authors.forename: M A
authors.initials: MA
authors.lastname: Mazzella
authors.forename: J J
authors.initials: JJ
authors.lastname: Casal
authors.forename: C L
authors.initials: CL
authors.lastname: Ballaré
mesh_terms: D017360:Arabidopsis / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects*; D029681:Arabidopsis Proteins; D018548:Cotyledon / Q000528:radiation effects; D009024:Morphogenesis; D010786:Photoreceptor Cells; D010834:Phytochrome / Q000378:metabolism*; D051939:Phytochrome B; D014157:Transcription Factors; D014466:Ultraviolet Rays
chemical_list: D029681:Arabidopsis Proteins; C497952:PHYB protein, Arabidopsis; D014157:Transcription Factors; D010834:Phytochrome; D051939:Phytochrome B