title: Toward the storage metabolome: profiling the barley vacuole.
abstract: While recent years have witnessed dramatic advances in our capacity to identify and quantify an ever-increasing number of plant metabolites, our understanding of how metabolism is spatially regulated is still far from complete. In an attempt to partially address this question, we studied the storage metabolome of the barley (Hordeum vulgare) vacuole. For this purpose, we used highly purified vacuoles isolated by silicon oil centrifugation and compared their metabolome with that found in the mesophyll protoplast from which they were derived. Using a combination of gas chromatography-mass spectrometry and Fourier transform-mass spectrometry, we were able to detect 59 (primary) metabolites for which we know the exact chemical structure and a further 200 (secondary) metabolites for which we have strong predicted chemical formulae. Taken together, these metabolites comprise amino acids, organic acids, sugars, sugar alcohols, shikimate pathway intermediates, vitamins, phenylpropanoids, and flavonoids. Of the 259 putative metabolites, some 12 were found exclusively in the vacuole and 34 were found exclusively in the protoplast, while 213 were common in both samples. When analyzed on a quantitative basis, however, there is even more variance, with more than 60 of these compounds being present above the detection limit of our protocols. The combined data were also analyzed with respect to the tonoplast proteome in an attempt to infer specificities of the transporter proteins embedded in this membrane. Following comparison with recent observations made using nonaqueous fractionation of Arabidopsis (Arabidopsis thaliana), we discuss these data in the context of current models of metabolic compartmentation in plants.
authors.affiliation: Max-Planck-Institute for Molecular Plant Physiology, 14476 Potsdam, Germany.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Tohge
authors.forename: Magali Schnell
authors.initials: MS
authors.lastname: Ramos
authors.forename: Adriano
authors.initials: A
authors.lastname: Nunes-Nesi
authors.forename: Marek
authors.initials: M
authors.lastname: Mutwil
authors.forename: Patrick
authors.initials: P
authors.lastname: Giavalisco
authors.forename: Dirk
authors.initials: D
authors.lastname: Steinhauser
authors.forename: Maja
authors.initials: M
authors.lastname: Schellenberg
authors.forename: Lothar
authors.initials: L
authors.lastname: Willmitzer
authors.forename: Staffan
authors.initials: S
authors.lastname: Persson
authors.forename: Enrico
authors.initials: E
authors.lastname: Martinoia
authors.forename: Alisdair R
authors.initials: AR
authors.lastname: Fernie
mesh_terms: D002853:Chromatography, Liquid; D016000:Cluster Analysis; D008401:Gas Chromatography-Mass Spectrometry; D053263:Gene Regulatory Networks / Q000235:genetics; D001467:Hordeum / Q000378:metabolism*; D053858:Metabolic Networks and Pathways / Q000235:genetics; D055442:Metabolome; D055432:Metabolomics / Q000379:methods*; D011523:Protoplasts / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D014617:Vacuoles / Q000378:metabolism*