title: Phenylalanine is required to promote specific developmental responses and prevents cellular damage in response to ultraviolet light in soybean (Glycine max) during the seed-to-seedling transition.
abstract: UV-radiation elicits a suite of developmental (photomorphogenic) and protective responses in plants, but responses early post-germination have received little attention, particularly in intensively bred plants of economic importance. We examined germination, hypocotyl elongation, leaf pubescence and subcellular responses of germinating and/or etiolated soybean (Glycine max (L.) Merr.) seedlings in response to treatment with discrete wavelengths of UV-A or UV-B radiation. We demonstrate differential responses of germinating/young soybean seedlings to a range of UV wavelengths that indicate unique signal transduction mechanisms regulate UV-initiated responses. We have investigated how phenylalanine, a key substrate in the phenylpropanoid pathway, may be involved in these responses. Pubescence may be a key location for phenylalanine-derived protective compounds, as UV-B irradiation increased pubescence and accumulation of UV-absorbing compounds within primary leaf pubescence, visualized by microscopy and absorbance spectra. Mass spectrometry analysis of pubescence indicated that sinapic esters accumulate in the UV-irradiated hairs compared to unirradiated primary leaf tissue. Deleterious effects of some UV-B wavelengths on germination and seedling responses were reduced or entirely prevented by inclusion of phenylalanine in the growth media. Key effects of phenylalanine were not duplicated by tyrosine or tryptophan or sucrose, nor is the specificity of response due to the absorbance of phenylalanine itself. These results suggest that in the seed-to-seedling transition, phenylalanine may be a limiting factor in the development of initial mechanisms of UV protection in the developing leaf.
authors.affiliation: Department of Plant Science and Landscape Architecture University of Maryland, College Park, Maryland, United States of America.
authors.forename: Joe H
authors.initials: JH
authors.lastname: Sullivan
authors.affiliation: Molecular, Cell and Developmental Program, Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois, United States of America.
authors.forename: DurreShahwar
authors.initials: D
authors.lastname: Muhammad
authors.affiliation: Molecular, Cell and Developmental Program, Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois, United States of America.
authors.forename: Katherine M
authors.initials: KM
authors.lastname: Warpeha
mesh_terms: D010649:Phenylalanine / Q000378:metabolism*; D018515:Plant Leaves / Q000254:growth & development*; D036226:Seedlings / Q000254:growth & development*; D012639:Seeds / Q000254:growth & development*; D013025:Glycine max / Q000254:growth & development*; D014466:Ultraviolet Rays / Q000009:adverse effects*
chemical_list: D010649:Phenylalanine