title: Effects of natural intensities of visible and ultraviolet radiation on epidermal ultraviolet screening and photosynthesis in grape leaves.
abstract: Grape (Vitis vinifera cv Silvaner) vine plants were cultivated under shaded conditions in the absence of ultraviolet (UV) radiation in a greenhouse, and subsequently placed outdoors under three different light regimes for 7 d. Different light regimes were produced by filters transmitting natural radiation, or screening out the UV-B (280-315 nm), or screening out the UV-A (315-400 nm) and the UV-B spectral range. During exposure, synthesis of UV-screening phenolics in leaves was quantified using HPLC: All treatments increased concentrations of hydroxycinnamic acids but the rise was highest, reaching 230% of the initial value, when UV radiation was absent. In contrast, UV-B radiation specifically increased flavonoid concentrations resulting in more than a 10-fold increase. Transmittance in the UV of all extracted phenolics was lower than epidermal UV transmittance determined fluorimetrically, and the two parameters were curvilinearly related. It is suggested that curvilinearity results from different absorption properties of the homogeneously dissolved phenolics in extracts and of the non-homogeneous distribution of phenolics in the epidermis. UV-B-dependent inhibition of maximum photochemical yield of photosystem II (PSII), measured as variable fluorescence of dark-adapted leaves, recovered in parallel to the buildup of epidermal screening for UV-B radiation, suggesting that PSII is protected against UV-B damage by epidermal screening. However, UV-B inhibition of CO(2) assimilation rates was not diminished by efficient UV-B screening. We propose that protection of UV-B inactivation of PSII is observed because preceding damage is efficiently repaired while those factors determining UV-B inhibition of CO(2) assimilation recover more slowly.
authors.affiliation: Lehrstuhl für Botanik II, Universität Würzburg, Julius-von-Sachs-Platz 3, D-97082 Würzburg, Germany.
authors.forename: C A
authors.initials: CA
authors.lastname: Kolb
authors.forename: M A
authors.initials: MA
authors.lastname: Käser
authors.forename: J
authors.initials: J
authors.lastname: Kopecký
authors.forename: G
authors.initials: G
authors.lastname: Zotz
authors.forename: M
authors.initials: M
authors.lastname: Riederer
authors.forename: E E
authors.initials: EE
authors.lastname: Pfündel
mesh_terms: D002109:Caffeic Acids / Q000302:isolation & purification / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D002734:Chlorophyll / Q000528:radiation effects*; D003373:Coumaric Acids / Q000302:isolation & purification / Q000378:metabolism; D005453:Fluorescence; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008954:Models, Biological; D010636:Phenols / Q000302:isolation & purification / Q000378:metabolism; D010788:Photosynthesis / Q000528:radiation effects*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000528:radiation effects; D045332:Photosystem II Protein Complex; D019441:Plant Epidermis / Q000528:radiation effects; D018515:Plant Leaves / Q000528:radiation effects; D014466:Ultraviolet Rays; D027843:Vitis / Q000528:radiation effects*
chemical_list: D002109:Caffeic Acids; D003373:Coumaric Acids; D045342:Light-Harvesting Protein Complexes; D010636:Phenols; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D002245:Carbon Dioxide