title: Light quality modulates metabolic synchronization over the diel phases of crassulacean acid metabolism.
abstract: Temporal compartmentation of carboxylation processes is a defining feature of crassulacean acid metabolism and involves circadian control of key metabolic and transport steps that regulate the supply and demand for carbon over a 24h cycle. Recent insights on the molecular workings of the circadian clock and its connection with environmental inputs raise new questions on the importance of light quality and, by analogy, certain photoreceptors for synchronizing the metabolic components of CAM. The present work tested the hypothesis that optimal coupling of stomatal conductance, net CO2 uptake, and the reciprocal turnover of carbohydrates and organic acids over the diel CAM cycle requires both blue and red light input signals. Contrasting monochromatic wavelengths of blue, green, and red light (i.e. 475, 530, 630nm) with low fluence rates (10 μmol m(-2) s(-1)) were administered for 16 hours each diel cycle for a total treatment time of 48 hours to the obligate CAM bromeliad, Aechmea 'Maya'. Of the light treatments imposed, low-fluence blue light was a key determinant in regulating stomatal responses, organic acid mobilization from the vacuole, and daytime decarboxylation. However, the reciprocal relationship between starch and organic acid turnover that is typical for CAM was uncoupled under low-fluence blue light. Under low-fluence red or green light, the diel turnover of storage carbohydrates was orchestrated in line with the requirements of CAM, but a consistent delay in acid consumption at dawn compared with plants under white or low-fluence blue light was noted. Consistent with the acknowledged influences of both red and blue light as input signals for the circadian clock, the data stress the importance of both red and blue-light signalling pathways for synchronizing the metabolic and physiological components of CAM over the day/night cycle.
authors.affiliation: Faculty of Engineering Technology, Department of Microbial and Molecular systems, Bioengineering Technology TC, KU Leuven Campus Geel, Kleinhoefstraat 4, B-2440 Geel, Belgium johan.ceusters@kuleuven.be.
authors.forename: Johan
authors.initials: J
authors.lastname: Ceusters
authors.affiliation: School of Biology, Newcastle Institute for Research on Sustainability, Devonshire Building, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6407, USA.
authors.forename: Anne M
authors.initials: AM
authors.lastname: Borland
authors.affiliation: School of Biology, Newcastle Institute for Research on Sustainability, Devonshire Building, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK.
authors.forename: Tahar
authors.initials: T
authors.lastname: Taybi
authors.affiliation: Faculty of Engineering Technology, Department of Microbial and Molecular systems, Bioengineering Technology TC, KU Leuven Campus Geel, Kleinhoefstraat 4, B-2440 Geel, Belgium.
authors.forename: Mario
authors.initials: M
authors.lastname: Frans
authors.affiliation: Faculty of Bioscience Engineering, Department of Biosystems, Division of Crop Biotechnics, KU Leuven, Willem De Croylaan 42, B-3001 Heverlee, Belgium.
authors.forename: Christof
authors.initials: C
authors.lastname: Godts
authors.affiliation: Faculty of Bioscience Engineering, Department of Biosystems, Division of Crop Biotechnics, KU Leuven, Willem De Croylaan 42, B-3001 Heverlee, Belgium.
authors.forename: Maurice P
authors.initials: MP
authors.lastname: De Proft
mesh_terms: D031229:Bromeliaceae / Q000235:genetics / Q000502:physiology / Q000528:radiation effects*; D002245:Carbon Dioxide / Q000378:metabolism*; D057906:Circadian Clocks; D006863:Hydrogen-Ion Concentration; D008027:Light; D019764:Phosphoenolpyruvate Carboxykinase (ATP) / Q000235:genetics / Q000378:metabolism; D010730:Phosphoenolpyruvate Carboxylase / Q000235:genetics / Q000378:metabolism; D010788:Photosynthesis; D018515:Plant Leaves / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D054046:Plant Stomata / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D018526:Plant Transpiration; D015398:Signal Transduction; D014867:Water / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D014867:Water; D002245:Carbon Dioxide; D010730:Phosphoenolpyruvate Carboxylase; D019764:Phosphoenolpyruvate Carboxykinase (ATP)
keywords: CAM; PEPC; PEPCK; carbohydrate; gas exchange; light quality; titratable acidity.