title: Analysis of Arabidopsis with highly reduced levels of malate and fumarate sheds light on the role of these organic acids as storage carbon molecules.
abstract: While malate and fumarate participate in a multiplicity of pathways in plant metabolism, the function of these organic acids as carbon stores in C(3) plants has not been deeply addressed. Here, Arabidopsis (Arabidopsis thaliana) plants overexpressing a maize (Zea mays) plastidic NADP-malic enzyme (MEm plants) were used to analyze the consequences of sustained low malate and fumarate levels on the physiology of this C(3) plant. When grown in short days (sd), MEm plants developed a pale-green phenotype with decreased biomass and increased specific leaf area, with thin leaves having lower photosynthetic performance. These features were absent in plants growing in long days. The analysis of metabolite levels of rosettes from transgenic plants indicated similar disturbances in both sd and long days, with very low levels of malate and fumarate. Determinations of the respiratory quotient by the end of the night indicated a shift from carbohydrates to organic acids as the main substrates for respiration in the wild type, while MEm plants use more reduced compounds, like fatty acids and proteins, to fuel respiration. It is concluded that the alterations observed in sd MEm plants are a consequence of impairment in the supply of carbon skeletons during a long dark period. This carbon starvation phenotype observed at the end of the night demonstrates a physiological role of the C(4) acids, which may be a constitutive function in plants.
authors.affiliation: Botanisches Institut, Biowissenschaftliches Zentrum, Universität zu Köln, 50674 Cologne, Germany.
authors.forename: Martina B
authors.initials: MB
authors.lastname: Zell
authors.forename: Holger
authors.initials: H
authors.lastname: Fahnenstich
authors.forename: Alexandra
authors.initials: A
authors.lastname: Maier
authors.forename: Mariana
authors.initials: M
authors.lastname: Saigo
authors.forename: Elena V
authors.initials: EV
authors.lastname: Voznesenskaya
authors.forename: Gerald E
authors.initials: GE
authors.lastname: Edwards
authors.forename: Carlos
authors.initials: C
authors.lastname: Andreo
authors.forename: Frank
authors.initials: F
authors.lastname: Schleifenbaum
authors.forename: Christiane
authors.initials: C
authors.lastname: Zell
authors.forename: María F
authors.initials: MF
authors.lastname: Drincovich
authors.forename: Verónica G
authors.initials: VG
authors.lastname: Maurino
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D002734:Chlorophyll / Q000032:analysis; D002736:Chloroplasts / Q000648:ultrastructure; D005453:Fluorescence; D005650:Fumarates / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D008293:Malates / Q000378:metabolism*; D046529:Microscopy, Electron, Transmission; D010641:Phenotype; D030821:Plants, Genetically Modified / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
chemical_list: D005650:Fumarates; D008293:Malates; D002734:Chlorophyll; D002245:Carbon Dioxide; D002244:Carbon; C030298:malic acid; C032005:fumaric acid