title: Carbon allocation from source to sink leaf tissue in relation to flavonoid biosynthesis in variegated Pelargonium zonale under UV-B radiation and high PAR intensity.
abstract: We studied the specific effects of high photosynthetically active radiation (PAR, 400-700 nm) and ecologically relevant UV-B radiation (0.90 W m(-2)) on antioxidative and phenolic metabolism by exploiting the green-white leaf variegation of Pelargonium zonale plants. This is a suitable model system for examining "source-sink" interactions within the same leaf. High PAR intensity (1350 μmol m(-2) s(-1)) and UV-B radiation induced different responses in green and white leaf sectors. High PAR intensity had a greater influence on green tissue, triggering the accumulation of phenylpropanoids and flavonoids with strong antioxidative function. Induced phenolics, together with ascorbate, ascorbate peroxidase (APX, EC 1.11.1.11) and catalase (CAT, EC 1.11.1.6) provided efficient defense against potential oxidative pressure. UV-B-induced up-regulation of non-phenolic H2O2 scavengers in green leaf sectors was greater than high PAR-induced changes, indicating a UV-B role in antioxidative defense under light excess; on the contrary, minimal effects were observed in white tissue. However, UV-B radiation had greater influence on phenolics in white leaf sections compared to green ones, inducing accumulation of phenolic glycosides whose function was UV-B screening rather than antioxidative. By stimulation of starch and sucrose breakdown and carbon allocation in the form of soluble sugars from "source" (green) tissue to "sink" (white) tissue, UV-B radiation compensated the absence of photosynthetic activity and phenylpropanoid and flavonoid biosynthesis in white sectors.
authors: Institute for Multidisciplinary Research, University of Belgrade, Kneza Viseslava 1, 11000 Belgrade, Serbia. Electronic address: marija@imsi.rs.
authors: Marija
authors: M
authors: Vidović
authors: Institute for Multidisciplinary Research, University of Belgrade, Kneza Viseslava 1, 11000 Belgrade, Serbia. Electronic address: filkis14@hotmail.com.
authors: Filis
authors: F
authors: Morina
authors: Institute for Multidisciplinary Research, University of Belgrade, Kneza Viseslava 1, 11000 Belgrade, Serbia. Electronic address: soonjam@gmail.com.
authors: Sonja
authors: S
authors: Milić
authors: Research Unit Environmental Simulation, Helmholtz Zentrum München, Ingolstädter Landstr. 1, 85764 Neuherberg, Germany. Electronic address: andreas.albert@helmholtz-muenchen.de.
authors: Andreas
authors: A
authors: Albert
authors: Baylor University, Center for Microscopy and Imaging, One Bear Place #97046, Waco, TX 76798-7046, USA. Electronic address: Bernd_Zechmann@baylor.edu.
authors: Bernd
authors: B
authors: Zechmann
authors: Faculty of Chemistry, University of Belgrade, PO Box 51, 11001 Belgrade, Serbia. Electronic address: tosti@chem.bg.ac.rs.
authors: Tomislav
authors: T
authors: Tosti
authors: Research Unit Environmental Simulation, Helmholtz Zentrum München, Ingolstädter Landstr. 1, 85764 Neuherberg, Germany. Electronic address: bwinkler@helmholtz-muenchen.de.
authors: Jana Barbro
authors: JB
authors: Winkler
authors: Institute for Multidisciplinary Research, University of Belgrade, Kneza Viseslava 1, 11000 Belgrade, Serbia. Electronic address: sonjavel@imsi.rs.
authors: Sonja Veljović
authors: SV
authors: Jovanović
mesh_terms: D000975:Antioxidants / Q000378:metabolism; D060387:Ascorbate Peroxidases / Q000235:genetics / Q000378:metabolism; D002244:Carbon / Q000378:metabolism*; D002374:Catalase / Q000235:genetics / Q000378:metabolism; D005419:Flavonoids / Q000096:biosynthesis* / Q000235:genetics; D031314:Geraniaceae / Q000235:genetics / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D000975:Antioxidants; D005419:Flavonoids; D010940:Plant Proteins; D002244:Carbon; D006861:Hydrogen Peroxide; D060387:Ascorbate Peroxidases; D002374:Catalase
keywords: Anthocyanins; Antioxidative enzymes; Flavonoids; High light intensity; Sugar distribution; UV-B radiation; Variegation