title: phyB-1 sorghum maintains responsiveness to simulated shade, irradiance and red light: far-red light.
abstract: The sorghum [Sorghum bicolor (L.) Moench] phyB-1 mutant exhibits a constitutive shade-avoidance phenotype including excessive shoot elongation. It was previously shown that this mutant also overproduces ethylene. Although phytochrome B (phyB) is assumed to be the pigment most important in sensing and transducing shade signals, the sorghum phyB-1 mutant still responds to light signals characteristic of shade. Specifically, it was determined that the leaf blade : leaf sheath elongation of phyB-1 is responsive to red : far red (R : FR), but this response is opposite that of wild type (WT). Reducing the photosynthetic photon flux density (PPFD) strongly reduced the leaf blade : leaf sheath of WT but did not affect phyB-1, demonstrating a role for phyB in sensing PPFD. Using light-emitting diode (LED) lighting, it was found that WT ethylene production was increased with low R : FR while PPFD had no effect. Conversely, phyB-1 ethylene production increased only with high PPFD, high R : FR which was the treatment resulting in the least ethylene production by WT. Elevated ethylene production inhibits shoot elongation, but may contribute to shade avoidance by reducing leaf blade : leaf sheath elongation. Ethylene responses to light treatments designed to promote or reduce phytochrome A (phyA) activity, and the analysis of PHYA levels in the two cultivars suggests that phyA could be involved in transducing shade signals in light-grown sorghum. Responses potentially tranduced by phyA are elevated in phyB-1 which also over-expresses PHYA.
authors.affiliation: Department of Soil and Crop Sciences, Texas A&M University, College Station, TX 77843-2474, USA. sfinlayson@tamu.edu
authors.forename: Scott A
authors.initials: SA
authors.lastname: Finlayson
authors.forename: Dirk B
authors.initials: DB
authors.lastname: Hays
authors.forename: Page W
authors.initials: PW
authors.lastname: Morgan
mesh_terms: D005030:Ethylenes / Q000378:metabolism; D008027:Light; D051942:Phytochrome A / Q000378:metabolism; D051939:Phytochrome B / Q000235:genetics / Q000502:physiology*; D018515:Plant Leaves / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D015398:Signal Transduction / Q000235:genetics; D045868:Sorghum / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects
chemical_list: D005030:Ethylenes; D051942:Phytochrome A; D051939:Phytochrome B; C036216:ethylene