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Jung B, Ludewig F, Schulz A, Meißner G, Wöstefeld N, Flügge UI, Pommerrenig B, Wirsching P, Sauer N, Koch W, Sommer F, Mühlhaus T, Schroda M, Cuin TA, Graus D, Marten I, Hedrich R, Neuhaus HE. Identification of the transporter responsible for sucrose accumulation in sugar beet taproots. NATURE PLANTS 2015; 1:14001. [PMID: 27246048 DOI: 10.1038/nplants.2014.1] [Citation(s) in RCA: 95] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2014] [Accepted: 09/24/2014] [Indexed: 05/21/2023]
Abstract
Sugar beet provides around one third of the sugar consumed worldwide and serves as a significant source of bioenergy in the form of ethanol. Sucrose accounts for up to 18% of plant fresh weight in sugar beet. Most of the sucrose is concentrated in the taproot, where it accumulates in the vacuoles. Despite 30 years of intensive research, the transporter that facilitates taproot sucrose accumulation has escaped identification. Here, we combine proteomic analyses of the taproot vacuolar membrane, the tonoplast, with electrophysiological analyses to show that the transporter BvTST2.1 is responsible for vacuolar sucrose uptake in sugar beet taproots. We show that BvTST2.1 is a sucrose-specific transporter, and present evidence to suggest that it operates as a proton antiporter, coupling the import of sucrose into the vacuole to the export of protons. BvTST2.1 exhibits a high amino acid sequence similarity to members of the tonoplast monosaccharide transporter family in Arabidopsis, prompting us to rename this group of proteins 'tonoplast sugar transporters'. The identification of BvTST2.1 could help to increase sugar yields from sugar beet and other sugar-storing plants in future breeding programs.
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Affiliation(s)
- Benjamin Jung
- Pflanzenphysiologie, University Kaiserslautern, Erwin Schrödinger Straße, D-67653 Kaiserslautern, Germany
| | - Frank Ludewig
- Biocenter Cologne, Botanical Institute II and Cluster of Excellence on Plant Sciences (CEPLAS), University of Cologne, Zülpicher Straße 47b, D-50674, Germany
| | - Alexander Schulz
- Biophysics and Molecular Plant Physiology, University Würzburg, Julius von Sachs Platz 2, D-97082 Würzburg, Germany
| | - Garvin Meißner
- Pflanzenphysiologie, University Kaiserslautern, Erwin Schrödinger Straße, D-67653 Kaiserslautern, Germany
| | - Nicole Wöstefeld
- Biocenter Cologne, Botanical Institute II and Cluster of Excellence on Plant Sciences (CEPLAS), University of Cologne, Zülpicher Straße 47b, D-50674, Germany
| | - Ulf-Ingo Flügge
- Biocenter Cologne, Botanical Institute II and Cluster of Excellence on Plant Sciences (CEPLAS), University of Cologne, Zülpicher Straße 47b, D-50674, Germany
| | - Benjamin Pommerrenig
- Molecular Plant Physiology, University Erlangen-Nuremberg, Staudtstraße 5, D-91058 Erlangen, Germany
| | - Petra Wirsching
- Molecular Plant Physiology, University Erlangen-Nuremberg, Staudtstraße 5, D-91058 Erlangen, Germany
| | - Norbert Sauer
- Molecular Plant Physiology, University Erlangen-Nuremberg, Staudtstraße 5, D-91058 Erlangen, Germany
| | - Wolfgang Koch
- KWS Saat AG, Grimsehlstr.31, D37555 Einbeck, Germany
| | - Frederik Sommer
- Molecular Biotechnology and Systems Biology, University Kaiserslautern, Paul-Ehrlich-Straße, D-67653 Kaiserslautern Germany
| | - Timo Mühlhaus
- Molecular Biotechnology and Systems Biology, University Kaiserslautern, Paul-Ehrlich-Straße, D-67653 Kaiserslautern Germany
| | - Michael Schroda
- Molecular Biotechnology and Systems Biology, University Kaiserslautern, Paul-Ehrlich-Straße, D-67653 Kaiserslautern Germany
| | - Tracey Ann Cuin
- Biophysics and Molecular Plant Physiology, University Würzburg, Julius von Sachs Platz 2, D-97082 Würzburg, Germany
| | - Dorothea Graus
- Biophysics and Molecular Plant Physiology, University Würzburg, Julius von Sachs Platz 2, D-97082 Würzburg, Germany
| | - Irene Marten
- Biophysics and Molecular Plant Physiology, University Würzburg, Julius von Sachs Platz 2, D-97082 Würzburg, Germany
| | - Rainer Hedrich
- Biophysics and Molecular Plant Physiology, University Würzburg, Julius von Sachs Platz 2, D-97082 Würzburg, Germany
| | - H Ekkehard Neuhaus
- Pflanzenphysiologie, University Kaiserslautern, Erwin Schrödinger Straße, D-67653 Kaiserslautern, Germany
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Functional characterization of a putative disaccharide membrane transporter in crustacean intestine. J Comp Physiol B 2014; 185:173-83. [DOI: 10.1007/s00360-014-0876-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Revised: 11/07/2014] [Accepted: 11/11/2014] [Indexed: 10/24/2022]
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Niland S, Schmitz K. Sugar Transport into Storage Tubers ofStachys sieboldiiMiq.: Evidence for Symplastic Unloading and Stachyose Uptake into Storage Vacuoles by an H+-Antiport Mechanism*. ACTA ACUST UNITED AC 2014. [DOI: 10.1111/j.1438-8677.1995.tb00827.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Klemens PA, Patzke K, Deitmer J, Spinner L, Le Hir R, Bellini C, Bedu M, Chardon F, Krapp A, Neuhaus HE. Overexpression of the vacuolar sugar carrier AtSWEET16 modifies germination, growth, and stress tolerance in Arabidopsis. PLANT PHYSIOLOGY 2013; 163:1338-52. [PMID: 24028846 PMCID: PMC3813654 DOI: 10.1104/pp.113.224972] [Citation(s) in RCA: 174] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2013] [Accepted: 09/11/2013] [Indexed: 05/18/2023]
Abstract
Here, we report that SUGARS WILL EVENTUALLY BE EXPORTED TRANSPORTER (SWEET16) from Arabidopsis (Arabidopsis thaliana) is a vacuole-located carrier, transporting glucose (Glc), fructose (Fru), and sucrose (Suc) after heterologous expression in Xenopus laevis oocytes. The SWEET16 gene, similar to the homologs gene SWEET17, is mainly expressed in vascular parenchyma cells. Application of Glc, Fru, or Suc, as well as cold, osmotic stress, or low nitrogen, provoke the down-regulation of SWEET16 messenger RNA accumulation. SWEET16 overexpressors (35SPro:SWEET16) showed a number of peculiarities related to differences in sugar accumulation, such as less Glc, Fru, and Suc at the end of the night. Under cold stress, 35SPro:SWEET16 plants are unable to accumulate Fru, while under nitrogen starvation, both Glc and Fru, but not Suc, were less abundant. These changes of individual sugars indicate that the consequences of an increased SWEET16 activity are dependent upon the type of external stimulus. Remarkably, 35SPro:SWEET16 lines showed improved germination and increased freezing tolerance. The latter observation, in combination with the modified sugar levels, points to a superior function of Glc and Suc for frost tolerance. 35SPro:SWEET16 plants exhibited increased growth efficiency when cultivated on soil and showed improved nitrogen use efficiency when nitrate was sufficiently available, while under conditions of limiting nitrogen, wild-type biomasses were higher than those of 35SPro:SWEET16 plants. Our results identify SWEET16 as a vacuolar sugar facilitator, demonstrate the substantial impact of SWEET16 overexpression on various critical plant traits, and imply that SWEET16 activity must be tightly regulated to allow optimal Arabidopsis development under nonfavorable conditions.
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Etxeberria E, Pozueta-Romero J, Gonzalez P. In and out of the plant storage vacuole. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2012; 190:52-61. [PMID: 22608519 DOI: 10.1016/j.plantsci.2012.03.010] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Revised: 03/15/2012] [Accepted: 03/29/2012] [Indexed: 05/08/2023]
Abstract
The plant storage vacuole is involved in a wide variety of metabolic functions a great many of which necessitate the transport of substances across the tonoplast. Some solutes, depending on the origin, have to cross the plasma membrane as well. The cell is equipped with a complex web of transport systems, cellular routes, and unique intracellular environments that support their transport and accumulation against a concentration gradient. These are capable of processing a diverse nature of substances of distinct sizes, chemical properties, and origins. In this review we describe the various mechanism involved in solute transport into the vacuole of storage cells with special emphasis placed on solutes arriving through the apoplast. Transport of solutes from the cytosol to the vacuole is carried out by tonoplast-bound ABC transporters, solute/H(+) antiporters, and ion channels whereas transport from the apoplast requires additional plasma membrane-bound solute/H(+) symporters and fluid-phase endocytosis. In addition, and based on new evidence accumulated within the last decade, we re-evaluate the current notion of extracellular solute uptake as partially based on facilitated diffusion, and offer an alternative interpretation that involves membrane bound transporters and fluid-phase endocytosis. Finally, we make several assertions in regards to solute export from the vacuole as predicted by the limited available data suggesting that both membrane-bound carriers and vesicle mediated exocytosis are involved during solute mobilization.
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Affiliation(s)
- Ed Etxeberria
- University of Florida/IFAS, Department of Horticultural Sciences, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred, FL 33850, USA.
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Yamamoto H, Suzuki M, Suga Y, Fukui H, Tabata M. Participation of an active transport system in berberine-secreting cultured cells of Thalictrum minus. PLANT CELL REPORTS 1987; 6:356-359. [PMID: 24248844 DOI: 10.1007/bf00269559] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/1987] [Revised: 07/07/1987] [Indexed: 06/02/2023]
Abstract
The release of the benzylisoquinoline alkaloid berberine from cultured cells of Thalictrum minus into the medium proved to be temperature-dependent and was suppressed by such inhibitors of the plasma membrane-bound ATPase as vanadate and diethylstilbestrol. These results indicate that berberine is secreted through an energy-requiring process located in the plasma membrane of berberine-producing T. minus cells. This is the first finding that a secondary metabolite of plant cell culture is secreted by an active transport system.
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Affiliation(s)
- H Yamamoto
- Faculty of Pharmaceutical Sciences, Kyoto University, Yoshida, Sakyo-ku, 606, Kyoto, Japan
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Hopp W, Seitz HU. The uptake of acylated anthocyanin into isolated vacuoles from a cell suspension culture of Daucus carota. PLANTA 1987; 170:74-85. [PMID: 24232844 DOI: 10.1007/bf00392383] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/1986] [Accepted: 09/03/1986] [Indexed: 06/02/2023]
Abstract
Anthocyanin-containing vacuoles were isolated from protoplasts of a cell suspension culture of Daucus carota. The vacuoles were stable for at least 2 h as demonstrated by the fact that they showed no efflux of anthocyanin. The uptake of radioactively labelled anthocyanin was time-dependent with a pH optimum at 7.5, and could be inhibited by the protonophore carbonylcyanide m-chlorophenylhydrazone. Furthermore, the transport was specific, since vacuoles from other plant species showed no uptake of labelled anthocyanin, and strongly depended on acylation with sinapic acid, as deacylated glycosides were not taken up by isolated vacuoles. Hence, it is suggested that the acylation of anthocyanin, which is also required for the stabilization of colour in vacuoles, is important for transport, and that acylated anthocyanin is transported by a selective carrier and might be trapped by a pH-dependent conformational change of the molecule inside the acid vacuolar sap.
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Affiliation(s)
- W Hopp
- Auf der Morgenstelle 1, Institut für Biologie I der Universität, D-7400, Tübingen, Federal Republic of Germany
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Deus-Neumann B, Zenk MH. Accumulation of alkaloids in plant vacuoles does not involve an ion-trap mechanism. PLANTA 1986; 167:44-53. [PMID: 24241730 DOI: 10.1007/bf00446367] [Citation(s) in RCA: 34] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/1985] [Indexed: 06/02/2023]
Abstract
Alkaloid uptake into vacuoles isolated from a Fumaria capreolata L. cell suspension culture was investigated. The uptake is carrier-mediated as shown by its substrate saturation, its sensitivity to metabolic inhibitors and especially by its exclusive preference for the (S)-forms of reticuline and scoulerine while the (R)-enantiomers which do not occur in this plant species were strictly discriminated. The carrier has a high affinity for (S)-reticuline with a K m=0.3 μM. The rate of alkaloid uptake was 6 pmol·h(-1)·μl(-1) vacuole, and 0.03 mg alkaloid·mg(-1) vacuolar protein were taken up. Transport was stimulated five-to seven-fold by ATP and was inhibited by the ATPase inhibitors N,N'-dicyclohexylcarbodiimide and 4-4'-diisothiocyanatostilbene-2,2' disulfonic acid, as well as by the protonophore carbonyl cyanide m-chlorophenylhydrazone. A number of alkaloids did not compete with labelled (S)-reticuline for uptake into vacuoles. The uptake system is absolutely specific for alkaloids indigenous to the plant from which the vacuoles were isolated. Slight modifications of the topography of an alkaloid molecule even with full retention of its electrical charge results in its exclusion. Alkaloid efflux was also shown to be mediated by a highly specific energy-dependent carrier. These results contradict the previously proposed ion-trap mechanism for alkaloid accumulation in vacuoles. A highly specific carrier-mediated and energy-dependent proton antiport system for alkaloid uptake and release is postulated.
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Affiliation(s)
- B Deus-Neumann
- Lehrstuhl Pharmazeutische Biologie, Universität München, Karlstrasse 29, D-8000, München 2, Germany
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11
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Niemietz C, Willenbrink J. The function of tonoplast ATPase in intact vacuoles of red beet is governed by direct and indirect ion effects. PLANTA 1985; 166:545-549. [PMID: 24241621 DOI: 10.1007/bf00391280] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/1985] [Accepted: 08/01/1985] [Indexed: 06/02/2023]
Abstract
The pH gradient and the electric potential across the tonoplast in mechanically isolated beetroot vacuoles has been studied by following the uptake of [(14)C]methylamine and [(14)C]triphenyl-methylphosphoniumchloride. In response to Mg-ATP, the vacuolar interior is acidified by 0.8 units. This strong acidification is accompanied by a slight hyperpolarization of the membrane potential, which is probably caused by a proton diffusion potential. In preparations where only a small acidification (0.4 units) occurred, the membrane potential was depolarized by the addition of Mg-ATP. Different monovalent cations and anions were tested concerning their effect on the pH gradient and ATPase activity in proton-conducting tonoplasts. Chloride stimulation and NO 3 (-) inhibition were clearly present. The observed decline of the pH gradient upon the addition of Na(+) salts is probably caused by an Na(+)/H(+) antiport system.
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Affiliation(s)
- C Niemietz
- Botanisches Institut, Lehrstuhl III, Universität zu Köln, Gyrhofstrasse 15, D-5000, Köln 41, Federal Republic of Germany
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Rataboul P, Alibert G, Boller T, Boudet AM. Intracellular transport and vacuolar accumulation of o-coumaric acid glucoside in Melitolus alba mesophyll cell protoplasts. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 1985. [DOI: 10.1016/0005-2736(85)90389-x] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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13
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Kaiser G, Heber U. Sucrose transport into vacuoles isolated from barley mesophyll protoplasts. PLANTA 1984; 161:562-8. [PMID: 24253927 DOI: 10.1007/bf00407090] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/1984] [Accepted: 03/08/1984] [Indexed: 05/24/2023]
Abstract
Sucrose transport has been investigated in vacuoles isolated from barley mesophyll protoplasts. Rates of sucrose transfer across the tonoplast were even higher in vitro than in vivo indicating that the sucrose transport system had not suffered damage during isolation of the vacuoles. Sucrose transport is carrier-mediated as shown by substrate saturation of transport and sensitivity to a metabolic inhibitor and to competitive substrates. A number of sugars, in particular maltose and raffinose, decreased uptake of sucrose. Sorbitol was slowly taken up but had no effect on sucrose transport. The SH-reagent p-chloromercuribenzene sulfonate inhibited sucrose uptake completely. The apparent Km of the carrier for sucrose uptake was 21 mM. Transport was neither influenced by ATP and pyrophosphate, with or without Mg(2+) present, nor by protonophores and valinomycin (with K(+) present). Apparently uptake was not energy dependent. Efflux experiments with preloaded vacuoles indicated that sucrose unloading from the isolated vavuoles is mediated by the same carrier which catalyses uptake. The vacuole of mesophyll cells appears to represent an intermediary storage compartment. Uptake of photosynthetic products into the vacuole during the light apparently minimizes osmotic swelling of the small cytosolic compartment of vacuolated leaf cells when photosynthetic productivity exceeds the capacity of the phloem for translocation of sugars.
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Affiliation(s)
- G Kaiser
- Lehrstuhl Botanik I der Universität, Mittlerer Dallenbergweg 64, D-8700, Würzburg, Federal Republic of Germany
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Deus-Neumann B, Zenk MH. A highly selective alkaloid uptake system in vacuoles of higher plants. PLANTA 1984; 162:250-260. [PMID: 24253097 DOI: 10.1007/bf00397447] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/1984] [Accepted: 06/15/1984] [Indexed: 06/02/2023]
Abstract
Vacuoles were isolated from different plant cell cultures and the transport mechanism for alkaloid uptake at the tonoplast membrane, as well as the compartmentation of enzymes and products inside the cells were investigated. While serpentine, the major alkaloid of Catharanthus roseus cells, is definitely located inside the vacuole, two key enzymes of the indole-alkaloid pathway, strictosidine synthase and a specific glucosidase, are located in the cytosol. Transport of alkaloids across the tonoplast into the vacuolar space has been characterized as an active, engergy-requiring mechanism, which is sensitive to the temperature and pH of the surrounding medium, stimulated by K(+) and Mg(2+), and inhibited by N,N'-dicyclohexylcarbodiimid and Cu(2+). The alkaloids accumulate inside the vacuoles against a concentration gradient, and the uptake system is specific for alkaloids indigenous to the plant from which the vacuoles have been isolated.
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Affiliation(s)
- B Deus-Neumann
- Lehrstuhl Pharmazeutische Biologie der Universität, Karlstrasse 29, D-8000, München 2, Germany
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Solute accumulation by grape pericarp cells II. Studies with protoplasts and isolated vacuoles. ACTA ACUST UNITED AC 1984. [DOI: 10.1016/s0015-3796(84)80074-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Peter Gogarten J, Bentrup FW. Fluxes and compartmentation of 3-O-methyl-D-glucose in Riccia fluitans : Hexose carrier in the plasmalemma has one substrate-binding site. PLANTA 1983; 159:423-431. [PMID: 24258295 DOI: 10.1007/bf00392078] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/1983] [Accepted: 06/20/1983] [Indexed: 06/02/2023]
Abstract
In thalli of the aquatic liverwort, Riccia fluitans, 3-O-methyl-D-glucose (3-OMG) is not metabolized. Intracellular compartmentation, accumulation and transmembrane fluxes of 3-OMG have been determined by compartmental analysis. A novel set of equations has been derived to extend this method to non-steady-state conditions of constant but unequal unidirectional fluxes. Efflux kinetics with 3-OMG and L-glucose revealed two intracellular flux compartments, presumably cytoplasm and vacuole; an additional quickly exchanging compartment (half-time approx. 1 min) has been assigned to the apoplast. With 1 mM 3-OMG given externally, cytoplasmic 3-OMG concentration (c c) attains a quasi-steady state of about 10 mM lasting for >100 h, whereas the presumed vacuolar concentration (c v) rises steadily, but does not reach flux equilibrium even after two weeks (c v=46 mM). After 24 h incubation with 0.03 mM 3-OMG, c c=1 mM approx., and c v=3 mM approx., thus indicating accumulation by active hexose transport at both the plasmalemma and tonoplast. External D-glucose, but no D-mannitol, competitively inhibits 3-OMG uptake (cis-inhibition) and stimulates 3-OMG efflux at the plasmalemma by a factor up to 2.5. This trans-stimulation saturates half-maximally at 1.5 mM D-glucose. It clearly indicates a hexose carrier in the plasmalemma with one substrate-binding site for D-glocose and 3-OMG, alternately exposed to the cytoplasmic and outside compartment. The extent of the measured trans-stimulation can only be explained, if in the transport cycle the translocation of the empty substrate-binding site across the plasmalemma is rate-limiting.
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Affiliation(s)
- J Peter Gogarten
- Institut für Botanik I der Universität, Senckenbergstrasse 17-21, D-6300, Giessen, Federal Republic of Germany
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Sauter JJ. Efflux and Reabsorption of Sugars in the Xylem II. Seasonal Changes in Sucrose Uptake in Salix. ACTA ACUST UNITED AC 1983. [DOI: 10.1016/s0044-328x(83)80007-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Kaeser W. Ultrastructure of Storage Cells in Jerusalem Artichoke Tubers (Helianthus tuberosus L.) Vesicle Formation During Inulin Synthesis. ACTA ACUST UNITED AC 1983. [DOI: 10.1016/s0044-328x(83)80084-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/30/2022]
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Doll S, Hauer R. Determination of the membrane potential of vacuoles isolated from red-beet storage tissue : Evidence for an electrogenic ATPase. PLANTA 1981; 152:153-8. [PMID: 24302383 DOI: 10.1007/bf00391187] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/1980] [Accepted: 02/02/1981] [Indexed: 05/23/2023]
Abstract
The membrane potential of isolated vacuoles of red beet (Beta vulgaris L.) was estimated using several methods. The quenching of the fluorescence of the cyanine dyes 3,3'-diethylthiodicarbocyanine iodide (DiS-C2-(5)) and 3,3'-dipropylthiodicarbocyanine iodide (DiS-C3-(5)) in vacuoles indicated a transmembrane potential difference, negative inside at low external potassium concentrations. The Δψ was found to be-55 mV with two other methods, the distribution of (204)T1(+) in the presence of valinomycin and the distribution of the lipophilic cation triphenylmethylphosphonium. Uncouplers reduced this value to-35 mV. High external potassium concentrations, comparable to cytosolic values, abolished the membrane potential almost completely. The addition of 1 mM Tris-Mg(2+)-ATP markedly hyperpolarized the membrane to-75 mV. This effect was prevented by inhibitors of the ATPase activity located in isolated vacuole membranes.
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Affiliation(s)
- S Doll
- Botanisches Institut der Universität, Gyrhofstraße 15, D-5000, Köln 41, Federal Republic of Germany
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