title: Endogenous circadian rhythms in pigment composition induce changes in photochemical efficiency in plant canopies.
abstract: There is increasing evidence that the circadian clock is a significant driver of photosynthesis that becomes apparent when environmental cues are experimentally held constant. We studied whether the composition of photosynthetic pigments is under circadian regulation, and whether pigment oscillations lead to rhythmic changes in photochemical efficiency. To address these questions, we maintained canopies of bean and cotton, after an entrainment phase, under constant (light or darkness) conditions for 30-48 h. Photosynthesis and quantum yield peaked at subjective noon, and non-photochemical quenching peaked at night. These oscillations were not associated with parallel changes in carbohydrate content or xanthophyll cycle activity. We observed robust oscillations of Chl a/b during constant light in both species, and also under constant darkness in bean, peaking when it would have been night during the entrainment (subjective nights). These oscillations could be attributed to the synthesis and/or degradation of trimeric light-harvesting complex II (reflected by the rhythmic changes in Chl a/b), with the antenna size minimal at night and maximal around subjective noon. Considering together the oscillations of pigments and photochemistry, the observed pattern of changes is counterintuitive if we assume that the plant strategy is to avoid photodamage, but consistent with a strategy where non-stressed plants maximize photosynthesis.
authors.affiliation: Department of Plant Biology and Ecology, University of the Basque Country (UPV/EHU), 48080, Bilbao, Spain.
authors.forename: José Ignacio
authors.identifier: http://orcid.org/0000-0001-6498-975X
authors.initials: JI
authors.lastname: García-Plazaola
authors.affiliation: Department of Plant Biology and Ecology, University of the Basque Country (UPV/EHU), 48080, Bilbao, Spain.|Institute of Botany, University of Innsbruck, A6020, Innsbruck, Austria.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Fernández-Marín
authors.affiliation: Department of Crop and Forest Sciences-AGROTECNIO Center, Universitat de Lleida, 25198, Lleida, Spain.|Departamento de Botánica, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Casilla 160-C, Concepción, Chile.
authors.forename: Juan Pedro
authors.initials: JP
authors.lastname: Ferrio
authors.affiliation: Department of Crop and Forest Sciences-AGROTECNIO Center, Universitat de Lleida, 25198, Lleida, Spain.
authors.forename: Josu G
authors.initials: JG
authors.lastname: Alday
authors.affiliation: Department of Environmental Sciences - Botany, University of Basel, Schönbeinstrasse 6, 4056, Basel, Switzerland.
authors.forename: Günter
authors.initials: G
authors.lastname: Hoch
authors.affiliation: Ecotron Européen de Montpellier, CNRS, UPS-3248, Montferrier-sur-Lez, France.
authors.forename: Damien
authors.initials: D
authors.lastname: Landais
authors.affiliation: Ecotron Européen de Montpellier, CNRS, UPS-3248, Montferrier-sur-Lez, France.|Centre d'Ecologie Fonctionnelle et Evolutive, CEFE-CNRS, UMR-5175, Université de Montpellier - Université Paul Valéry - EPHE, 1919 route de Mende, F-34293, Montpellier Cedex 5, France.
authors.forename: Alexandru
authors.initials: A
authors.lastname: Milcu
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Richmond, 2753, New South Wales, Australia.
authors.forename: David T
authors.initials: DT
authors.lastname: Tissue
authors.affiliation: Department of Crop and Forest Sciences-AGROTECNIO Center, Universitat de Lleida, 25198, Lleida, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Voltas
authors.affiliation: Swiss Federal Institute for Forest, Snow and Landscape Research, 8903, Birmensdorf, Switzerland.|Institute for Landscape Biogeochemistry, Leibniz-Centre for Agricultural Landscape Research (ZALF), 15374, Müncheberg, Germany.
authors.forename: Arthur
authors.initials: A
authors.lastname: Gessler
authors.affiliation: Ecotron Européen de Montpellier, CNRS, UPS-3248, Montferrier-sur-Lez, France.
authors.forename: Jacques
authors.initials: J
authors.lastname: Roy
authors.affiliation: Department of Crop and Forest Sciences-AGROTECNIO Center, Universitat de Lleida, 25198, Lleida, Spain.|Hawkesbury Institute for the Environment, Western Sydney University, Richmond, 2753, New South Wales, Australia.
authors.forename: Víctor
authors.initials: V
authors.lastname: Resco de Dios
mesh_terms: D050260:Carbohydrate Metabolism; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D002940:Circadian Rhythm / Q000502:physiology*; D003368:Gossypium / Q000502:physiology*; D027805:Phaseolus / Q000502:physiology*; D010788:Photosynthesis / Q000502:physiology*; D010860:Pigments, Biological / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism
chemical_list: D010860:Pigments, Biological; D002734:Chlorophyll; C037184:chlorophyll b; D000077194:Chlorophyll A
keywords: chlorophyll a/b; electron transport; photosynthesis; stomata