PD Dr. rer. nat. Christina Kühn

Profil

• Regulation und Mobilität von Saccharosetransportern

  Quelle ↗

  Förderer: DFG Sachbeihilfe Zeitraum: 03/2008 - 04/2009 Projektleitung: PD Dr. rer. nat. Christina Kühn

• SFB 429 III: Untersuchungen zu Interaktionen und Regulation von Saccharose-Transportproteinen aus Solanum tuberosum (Teilprojekt B 11)

  Quelle ↗

  Förderer: DFG Sonderforschungsbereich Zeitraum: 01/2005 - 12/2010 Projektleitung: PD Dr. rer. nat. Christina Kühn

• SPP 1530: Ein IDD Transkriptionsfaktor in der Regulation der Zucker-vermittelten Blühinduktion und Knollenbildung in Solanum tuberosum

  Quelle ↗

  Förderer: DFG Sachbeihilfe Zeitraum: 02/2015 - 06/2019 Projektleitung: PD Dr. rer. nat. Christina Kühn

• Untersuchungen zur Oligomerisierung und Regulation von Saccharosetransportproteinen in Solanum tuberosum

  Quelle ↗

  Förderer: DFG Sachbeihilfe Zeitraum: 10/2003 - 03/2005 Projektleitung: PD Dr. rer. nat. Christina Kühn

• Untersuchungen zur Regulation und Mobilität des Saccharosetransporters StSUT 1 aus Solanum tuberosum

  Quelle ↗

  Förderer: DFG Sachbeihilfe Zeitraum: 07/2005 - 08/2010 Projektleitung: PD Dr. rer. nat. Christina Kühn

• Landeskompetenzzentrum Forst Eberswalde

  PT

  50 Treffer57.3%
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    P

    57.3%
  • Entwicklung eines innovativen Kulturbegründungsverfahrens für Eichen zur Verbesserung der Wurzelentwicklung durch kompostierbare Wurzelhüllen
    P

    45.7%

• Landesbauernverband Brandenburg e.V.

  P

  27 Treffer57.0%
  • Sortenstrategien bei landwirtschaftlichen Nutzpflanzen zur Anpassung an den Klimawandel
    P

    57.0%

• Märkischer Saatgutverband Brandenburg e.V.

  P

  27 Treffer57.0%
  • Sortenstrategien bei landwirtschaftlichen Nutzpflanzen zur Anpassung an den Klimawandel
    P

    57.0%

• Landesamt für Verbraucherschutz, Landwirtschaft und Flurneuordnung Brandenburg

  P

  29 Treffer57.0%
  • Sortenstrategien bei landwirtschaftlichen Nutzpflanzen zur Anpassung an den Klimawandel
    P

    57.0%

• MSB Research, Development and Innovation gGmbH

  PT

  87 Treffer55.0%
  • FOR 5177/2: Korrelation der Leistungsfähigkeit der Lendenwirbelsäule mit klinischen Outcomes nach einer gezielten Behandlung bei Patienten mit unteren Rückenschmerzen (TP 04)
    P

    55.0%

• Bernstein Center for Computational Neuroscience Berlin

  PT

  46 Treffer54.2%
  • DFG-Sachbeihilfe: Aufmerksamkeit und sensorische Integration im aktiven Sehen von bewegten Objekten
    T

    54.2%
  • SFB 1315/2: Mechanismen und Störungen der Gedächtniskonsolidierung: Von Synapsen zur Systemebene
    P

    45.8%

• Sozio-oekonomische Panel (SOEP) am DIW Berlin

  PT

  3 Treffer54.0%
  • Verbundprojekt: Konzeption, Durchführung, Aufbereitung, Registerverknüpfung, Analyse und Datenbereitstellung bzw. Weitergabe einer repräsentativen Stichprobe „Geflüchtete Familien“ (GeFam) – Teilprojekt: Institutionelle Maßnahmen zur Arbeitsmarktintegration Geflüchteter
    P

    54.0%

• Zoologischer Garten Berlin AG

  P

  20 Treffer53.9%
  • Tiere zum Sprechen bringen. Logistik, Wissenschaft, Präsentation
    P

    53.9%

• Internationale Vereinigung der Bodenwissenschaften

  P

  11 Treffer53.8%
  • Langfristige Entwicklung der Bodenfruchtbarkeit sandiger Standorte unter dem Einfluss von ackerbaulichen Maßnahmen
    P

    53.8%

• Rothamsted Research

  P

  11 Treffer53.8%
  • Langfristige Entwicklung der Bodenfruchtbarkeit sandiger Standorte unter dem Einfluss von ackerbaulichen Maßnahmen
    P

    53.8%

• The Molecular Receptive Ranges of Human TAS2R Bitter Taste Receptors

  2009

  Chemical Senses · 1123 Zitationen · DOI

  Humans perceive thousands of compounds as bitter. In sharp contrast, only approximately 25 taste 2 receptors (TAS2R) bitter taste receptors have been identified, raising the question as to how the vast array of bitter compounds can be detected by such a limited number of sensors. To address this issue, we have challenged 25 human taste 2 receptors (hTAS2Rs) with 104 natural or synthetic bitter chemicals in a heterologous expression system. Thirteen cognate bitter compounds for 5 orphan receptors and 64 new compounds for previously identified receptors were discovered. Whereas some receptors recognized only few agonists, others displayed moderate or extreme tuning broadness. Thus, 3 hTAS2Rs together were able to detect approximately 50% of the substances used. Conversely, though 63 bitter substances activated only 1-3 receptors, 19 compounds stimulated up to 15 hTAS2Rs. Our data suggest that the detection of the numerous bitter chemicals is related to the molecular receptive ranges of hTAS2Rs.

• The Molecular Basis of Individual Differences in Phenylthiocarbamide and Propylthiouracil Bitterness Perception

  2005

  Current Biology · 699 Zitationen · DOI

• The cells and peripheral representation of sodium taste in mice

  2010

  Nature · 685 Zitationen · DOI

• Sucrose transporters of higher plants

  2010

  Current Opinion in Plant Biology · 457 Zitationen · DOI

• Macromolecular Trafficking Indicated by Localization and Turnover of Sucrose Transporters in Enucleate Sieve Elements

  1997

  Science · 453 Zitationen · DOI

  The leaf sucrose transporter SUT1 is essential for phloem loading and long-distance transport of assimilates. Both SUT1 messenger RNA (mRNA) and protein were shown to be diurnally regulated and to have high turnover rates. SUT1 protein was detected by immunolocalization in plasma membranes of enucleate sieve elements (SEs) in tobacco, potato, and tomato. Analysis by in situ hybridization showed that SUT1 mRNA localizes mainly to the SE and is preferentially associated with plasmodesmata. Antisense inhibition of SUT1 expression under control of a companion cell (CC)-specific promoter indicated synthesis of SUT1 mRNA in the CC. These results provide evidence for targeting of plant endogenous mRNA and potentially SUT1 protein through phloem plasmodesmata and for sucrose loading at the plasma membrane of SE.

• SUT2, a Putative Sucrose Sensor in Sieve Elements

  2000

  The Plant Cell · 351 Zitationen · DOI

  In leaves, sucrose uptake kinetics involve high- and low-affinity components. A family of low- and high-affinity sucrose transporters (SUT) was identified. SUT1 serves as a high-affinity transporter essential for phloem loading and long-distance transport in solanaceous species. SUT4 is a low-affinity transporter with an expression pattern overlapping that of SUT1. Both SUT1 and SUT4 localize to enucleate sieve elements of tomato. New sucrose transporter-like proteins, named SUT2, from tomato and Arabidopsis contain extended cytoplasmic domains, thus structurally resembling the yeast sugar sensors SNF3 and RGT2. Features common to these sensors are low codon bias, environment of the start codon, low expression, and lack of detectable transport activity. In contrast to LeSUT1, which is induced during the sink-to-source transition of leaves, SUT2 is more highly expressed in sink than in source leaves and is inducible by sucrose. LeSUT2 protein colocalizes with the low- and high-affinity sucrose transporters in sieve elements of tomato petioles, indicating that multiple SUT mRNAs or proteins travel from companion cells to enucleate sieve elements. The SUT2 gene maps on chromosome V of potato and is linked to a major quantitative trait locus for tuber starch content and yield. Thus, the putative sugar sensor identified colocalizes with two other sucrose transporters, differs from them in kinetic properties, and potentially regulates the relative activity of low- and high-affinity sucrose transport into sieve elements.

• Bitter Taste Receptors for Saccharin and Acesulfame K

  2004

  Journal of Neuroscience · 348 Zitationen · DOI

  Weight-conscious subjects and diabetics use the sulfonyl amide sweeteners saccharin and acesulfame K to reduce their calorie and sugar intake. However, the intrinsic bitter aftertaste, which is caused by unknown mechanisms, limits the use of these sweeteners. Here, we show by functional expression experiments in human embryonic kidney cells that saccharin and acesulfame K activate two members of the human TAS2R family (hTAS2R43 and hTAS2R44) at concentrations known to stimulate bitter taste. These receptors are expressed in tongue taste papillae. Moreover, the sweet inhibitor lactisole did not block the responses of cells transfected with TAS2R43 and TAS2R44, whereas it did block the response of cells expressing the sweet taste receptor heteromer hTAS1R2-hTAS1R3. The two receptors were also activated by nanomolar concentrations of aristolochic acid, a purely bitter-tasting compound. Thus, hTAS2R43 and hTAS2R44 function as cognate bitter taste receptors and do not contribute to the sweet taste of saccharin and acesulfame K. Consistent with the in vitro data, cross-adaptation studies in human subjects also support the existence of common receptors for both sulfonyl amide sweeteners.

• A New Subfamily of Sucrose Transporters, SUT4, with Low Affinity/High Capacity Localized in Enucleate Sieve Elements of Plants

  2000

  The Plant Cell · 316 Zitationen · DOI

  A new subfamily of sucrose transporters from Arabidopsis (AtSUT4), tomato (LeSUT4), and potato (StSUT4) was isolated, demonstrating only 47% similarity to the previously characterized SUT1. SUT4 from two plant species conferred sucrose uptake activity when expressed in yeast. The K(m) for sucrose uptake by AtSUT4 of 11.6 +/- 0.6 mM was approximately 10-fold greater than for all other plant sucrose transporters characterized to date. An ortholog from potato had similar kinetic properties. Thus, SUT4 corresponds to the low-affinity/high-capacity saturable component of sucrose uptake found in leaves. In contrast to SUT1, SUT4 is expressed predominantly in minor veins in source leaves, where high-capacity sucrose transport is needed for phloem loading. In potato and tomato, SUT4 was immunolocalized specifically to enucleate sieve elements, indicating that like SUT1, macromolecular trafficking is required to transport the mRNA or the protein from companion cells through plasmodesmata into the sieve elements.

• Sugar transporters in plants and in their interactions with fungi

  2012

  Trends in Plant Science · 297 Zitationen · DOI

• S3-Leitlinie „Magenkarzinom” -

  2011

  Zeitschrift für Gastroenterologie · 284 Zitationen · DOI

  Inhalt 1. Informationen zu dieser Leitlinie 462 1.1. Herausgeber 462 1.1.1. Federführende Fachgesellschaft 462 1.1.2. Kontakt 462 1.1.3. Verfügbare Dokumente zur Leitlinie 462 1.2. Besonderer Hinweis 462 1.3. Autoren dieser Leitlinie 462 1.4. Ziele des Leitlinienprogramms Onkologie 462 2. Einführung 463 2.1. Geltungsbereich und Zweck 463 2.1.1. Zielsetzung und Fragestellung 463 2.1.2. Adressaten 464 2.1.3. Verbreitung u. Implementierung d. Leitlinien 464 2.1.4. Finanzierung der Leitlinie und Darlegung möglicher Interessenskonflikte 464 2.1.5. Gültigkeitsdauer u. Aktualisierungsverfahren 465 2.2. Grundlagen der Methodik 465 2.2.1. Schema der Evidenzgraduierung nach Oxford 465 2.3. Verwendete Abkürzungen 466 3. Konsentierte und abgestimmte Empfehlungen 466 3.1. Risikofaktoren 466 3.1.1. Helicobacter pylori 466 3.1.2. Weitere Risikofaktoren 467 3.2. Risikogruppen 468 3.2.1. Familiäres Risiko 468 3.2.2. Hereditäres nonpolypöses kolorektales Karzinom (HNPCC) 469 3.3. Screening und Prävention 470 3.3.1. Screening 470 3.3.2. Prävention 471 3.4. Primärdiagnostik 472 3.4.1. Endoskopische Untersuchung 472 3.4.2. Staging 472 3.4.3. Histologie 472 3.5. Staging 473 3.5.1. Ultraschalldiagnostik 473 3.5.2. Röntgendiagnostik 474 3.5.3. Laparoskopie 475 3.5.4. Laborchemische Parameter 476 3.6. Histopathologie 476 3.7. Endoskopische Therapie 477 3.7.1. Resektion 477 3.7.2. Rezidiv 479 3.7.3. Komplikationen 479 3.7.4. Nachsorge 479 3.8. Chirurgische Therapie 479 3.8.1. Resektion 479 3.8.2. Rezidiv 483 3.8.3. Definitive Radiochemotherapie 483 3.9. Multimodale Therapie 483 3.9.1. Perioperative Chemotherapie 483 3.9.2. Präoperative Radiochemotherapie 488 3.9.3. Präoperative Antikörper-Therapie 488 3.9.4. Restaging nach neoadjuvanter Therapie 488 3.9.5. Postoperative Therapie 489 3.9.6. Adjuvante Therapiekonzepte 491 3.10. Tumorgerichtete palliative Therapie 493 3.10.1. Medikamentöse Tumortherapie 493 3.10.2. Vorgehen bei Tumoren ohne HER-2-Überexpression 494 3.10.3. Vorgehen bei HER-2-überexprimierenden/-amplifizierenden Tumoren 498 3.10.4. Zweit-Chemotherapie 498 3.11. Weitere palliative Situationen u. deren Therapie 499 3.11.1. Palliative Therapieoptionen 499 3.11.2. Therapie der Tumorblutung 500 3.11.3. Palliative operative Therapie 500 3.11.4. Chemotherapie-refraktärer maligner Aszites 500 3.12. Supportive Maßnahmen 501 3.12.1. Fatigue-Syndrom 501 3.12.2. Zusammenfassung weiterer Maßnahmen 501 3.13. Ernährung 505 3.13.1. Allgemeine Entscheidungshilfen 505 3.13.2. Präoperative Ernährungstherapie 506 3.13.3. Postoperative Ernährungstherapie 507 3.13.4. Ernährung unter Chemotherapie oder Strahlentherapie 507 3.13.5. Ernährung in der Sterbephase 509 3.14. Nachsorge und Rehabilitation 509 3.14.1. Lebensqualität 509 3.14.2. Substitutionen nach Gastrektomie 509 3.14.3. Rehabilitationsmaßnahmen 509 3.14.4. Bestimmung von Tumormarkern 510 3.15. Psychoonkologie 510 3.15.1. Patientennahes Informationsmanagement 510 3.15.2. Lebensqualität 510 3.15.3. Psychoonkologische Betreuung 511 3.16. Komplementäre Therapie 512 3.16.1. Abgestimmte Empfehlungen 512 3.16.2. Weitere Hinweise der Arbeitsgruppe zur komplementären Therapie 514 4. Qualitätsindikatoren 515 Literatur 517

• RNA Interference of LIN5 in Tomato Confirms Its Role in Controlling Brix Content, Uncovers the Influence of Sugars on the Levels of Fruit Hormones, and Demonstrates the Importance of Sucrose Cleavage for Normal Fruit Development and Fertility  

  2009

  PLANT PHYSIOLOGY · 272 Zitationen · DOI

  Abstract It has been previously demonstrated, utilizing intraspecific introgression lines, that Lycopersicum Invertase5 (LIN5), which encodes a cell wall invertase, controls total soluble solids content in tomato (Solanum lycopersicum). The physiological role of this protein, however, has not yet been directly studied, since evaluation of data obtained from the introgression lines is complicated by the fact that they additionally harbor many other wild species alleles. To allow a more precise comparison, we generated transgenic tomato in which we silenced the expression of LIN5 using the RNA interference approach. The transformants were characterized by an altered flower and fruit morphology, displaying increased numbers of petals and sepals per flower, an increased rate of fruit abortion, and a reduction in fruit size. Evaluation of the mature fruit revealed that the transformants were characterized by a reduction of seed number per plant. Furthermore, detailed physiological analysis revealed that the transformants displayed aberrant pollen morphology and a reduction in the rate of pollen tube elongation. Metabolite profiling of ovaries and green and red fruit revealed that metabolic changes in the transformants were largely confined to sugar metabolism, whereas transcript and hormone profiling revealed broad changes both in the hormones themselves and in transcripts encoding their biosynthetic enzymes and response elements. These results are discussed in the context of current understanding of the role of sugar during the development of tomato fruit, with particular focus given to its impact on hormone levels and organ morphology.

• Sucrose transporter LeSUT1 and LeSUT2 inhibition affects tomato fruit development in different ways

  2005

  The Plant Journal · 268 Zitationen · DOI

  Sucrose transporters of higher plants belong to a large gene family. At least four different sucrose transporters are known in Solanaceous plants, although their function remains to be elucidated in detail. The isolation of LeSUT1 and LeSUT2from Lycopersicon esculentum has been described earlier. Whereas SUT1 is supposed to be the main phloem loader of sucrose in Solanaceae, the role of SUT2 remains a matter of debate. A transgenic approach was taken to evaluate the potential functions of SUT2/SUC3 proteins in sucrose transport or sensing. Expression of LeSUT1 and LeSUT2 was inhibited independently in transgenic tomato plants, using the antisense technique, in order to analyse their specific functions. Although the phloem-specific inhibition of LeSUT1 antisense plants showed a phenotype consistent with an essential role in phloem loading, constitutive LeSUT2 antisense inhibition exclusively affected tomato fruit and seed development. Neither LeSUT1, nor the LeSUT2 antisense plants were able to produce normal tomato fruits; however, it is likely that independent mechanisms underlie these phenomena. While phloem loading was blocked in LeSUT1 antisense plants, the fertility of fruits was reduced in LeSUT2 antisense plants. A detailed physiological analysis of these plants established a role for SUT2 in pollen tube growth and thus assigned a physiological role for SUT2.

• Sucrose Transporter StSUT4 from Potato Affects Flowering, Tuberization, and Shade Avoidance Response

  2007

  PLANT PHYSIOLOGY · 252 Zitationen · DOI

  Sucrose (Suc) transporters belong to a large gene family. The physiological role of SUT1 proteins has been intensively investigated in higher plants, whereas that of SUT4 proteins is so far unknown. All three known Suc transporters from potato (Solanum tuberosum), SUT1, SUT2, and SUT4, are colocalized and their RNA levels not only follow a diurnal rhythm, but also oscillate in constant light. Here, we examined the physiological effects of transgenic potato plants on RNA interference (RNAi)-inactivated StSUT4 expression. The phenotype of StSUT4-RNAi plants includes early flowering, higher tuber production, and reduced sensitivity toward light enriched in far-red wavelength (i.e. in canopy shade). Inhibition of StSUT4 led to tuber production of the strict photoperiodic potato subsp. andigena even under noninductive long-day conditions. Accumulation of soluble sugars and Suc efflux from leaves of transgenic plants are modified in StSUT4-RNAi plants, leading to modified Suc levels in sink organs. StSUT4 expression of wild-type plants is induced by gibberellins and ethephon, and external supply of gibberellic acid leads to even more pronounced differences between wild-type and StSUT4-RNAi plants regarding tuber yield and internode elongation, indicating a reciprocal regulation of StSUT4 and gibberellins.

• Transport of cytokinins mediated by purine transporters of the PUP family expressed in phloem, hydathodes, and pollen of <i>Arabidopsis</i>

  2003

  The Plant Journal · 249 Zitationen · DOI

  Nucleobases and derivatives like cytokinins and caffeine are translocated in the plant vascular system. Transport studies in cultured Arabidopsis cells indicate that adenine and cytokinin are transported by a common H+-coupled high-affinity purine transport system. Transport properties are similar to that of Arabidopsis purine transporters AtPUP1 and 2. When expressed in yeast, AtPUP1 and 2 mediate energy-dependent high-affinity adenine uptake, whereas AtPUP3 activity was not detectable. Similar to the results from cell cultures, purine permeases (PUP) mediated uptake of adenine can be inhibited by cytokinins, indicating that cytokinins are transport substrates. Direct measurements demonstrate that AtPUP1 is capable of mediating uptake of radiolabeled trans-zeatin. Cytokinin uptake is strongly inhibited by adenine and isopentenyladenine but is poorly inhibited by 6-chloropurine. A number of physiological cytokinins including trans- and cis-zeatin are also efficient competitors for AtPUP2-mediated adenine uptake, suggesting that AtPUP2 is also able to mediate cytokinin transport. Furthermore, AtPUP1 mediates transport of caffeine and ribosylated purine derivatives in yeast. Promoter-reporter gene studies point towards AtPUP1 expression in the epithem of hydathodes and the stigma surface of siliques, suggesting a role in retrieval of cytokinins from xylem sap to prevent loss during guttation. The AtPUP2 promoter drives GUS reporter gene activity in the phloem of Arabidopsis leaves, indicating a role in long-distance transport of adenine and cytokinins. Promoter activity of AtPUP3 was only found in pollen. In summary, three closely related PUPs are differentially expressed in Arabidopsis and at least two PUPs have properties similar to the adenine and cytokinin transport system identified in Arabidopsis cell cultures.

• The H+-Sucrose Cotransporter NtSUT1 Is Essential for Sugar Export from Tobacco Leaves1

  1998

  PLANT PHYSIOLOGY · 242 Zitationen · DOI

  In many species translocation of sucrose from the mesophyll to the phloem is carrier mediated. A sucrose/H+-symporter cDNA, NtSUT1, was isolated from tobacco (Nicotiana tabacum) and shown to be highly expressed in mature leaves and at low levels in other tissues, including floral organs. To study the in vivo function of NtSUT1, tobacco plants were transformed with a SUT1 antisense construct under control of the cauliflower mosaic virus 35S promoter. Upon maturation, leaves of transformants expressing reduced amounts of SUT1 mRNA curled downward, and strongly affected plants developed chloroses and necroses that led to death. The leaves exhibited impaired ability to export recently fixed 14CO2 and were unable to export transient starch during extended periods of darkness. As a consequence, soluble carbohydrates accumulated and photosynthesis was reduced. Autoradiographs of leaves show a heterogenous pattern of CO2 fixation even after a 24-h chase. The 14C pattern does not change with time, suggesting that movement of photosynthate between mesophyll cells may also be impaired. The affected lines show a reduction in the development of the root system and delayed or impaired flowering. Taken together, the effects observed in a seed plant (tobacco) demonstrate the importance of SUT1 for sucrose loading into the phloem via an apoplastic route and possibly for intermesophyll transport as well.

• A New Family of High-Affinity Transporters for Adenine, Cytosine, and Purine Derivatives in Arabidopsis

  2000

  The Plant Cell · 226 Zitationen · DOI

  In many organisms, including plants, nucleic acid bases and derivatives such as caffeine are transported across the plasma membrane. Cytokinins, important hormones structurally related to adenine, are produced mainly in root apices, from where they are translocated to shoots to control a multitude of physiological processes. Complementation of a yeast mutant deficient in adenine uptake (fcy2) with an Arabidopsis cDNA expression library enabled the identification of a gene, AtPUP1 (for Arabidopsis thaliana purine permease1), belonging to a large gene family (AtPUP1 to AtPUP15) encoding a new class of small, integral membrane proteins. AtPUP1 transports adenine and cytosine with high affinity. Uptake is energy dependent, occurs against a concentration gradient, and is sensitive to protonophores, potentially indicating secondary active transport. Competition studies show that purine derivatives (e.g., hypoxanthine), phytohormones (e.g., zeatin and kinetin), and alkaloids (e.g., caffeine) are potent inhibitors of adenine and cytosine uptake. Inhibition by cytokinins is competitive (competitive inhibition constant K(i) = 20 to 35 microM), indicating that cytokinins are transported by this system. AtPUP1 is expressed in all organs except roots, indicating that the gene encodes an uptake system for root-derived nucleic acid base derivatives in shoots or that it exports nucleic acid base analogs from shoots by way of the phloem. The other family members may have different affinities for nucleic acid bases, perhaps functioning as transporters for nucleosides, nucleotides, and their derivatives.

• The human taste receptor hTAS2R14 responds to a variety of different bitter compounds

  2004

  Biochemical and Biophysical Research Communications · 223 Zitationen · DOI

• Companion cell‐specific inhibition of the potato sucrose transporter SUT1

  1996

  Plant Cell & Environment · 179 Zitationen · DOI

  ABSTRACT In many plants, translocation of sucrose from mesnsophyll to phloem for long‐distance transport is carrier‐mediated. The sucrose H + ‐symporter gene SUT1 from potato is expressed at high levels in the phloem of mature, exporting leaves and at lower levels in other organs. Inhibition of SUT1 by expression of an antisense gene in companion cells under control of the rolC promoter leads to accumulation of high amounts of soluble and insoluble carbohydrates in leaves and inhibition of photosynthesis. The distribution of in situ localized starch does not correspond with areas of reduced photosynthesis as shown by fluorescence imaging. Dissection of antisense effects on sink and source organs by reciprocal grafts shows that inhibition of transporter gene expression in leaves is sufficient to produce chlorosis in leaves and reduced tuber yield. In contrast to the arrest of plasmodesmal development found in plants that express yeast invertase in the apoplast, in mature leaves of sucrose transporter antisense plants plasmodesmata are branched and have median cavities. These data strongly support an apoplastic mode of phloem loading in potato, in which the sucrose transporter located at the plasma membrane of the sieve element/companion cell complex represents the primary route for sugar uptake into the long‐distance translocation pathway.

• Protein–Protein Interactions between Sucrose Transporters of Different Affinities Colocalized in the Same Enucleate Sieve Element

  2002

  The Plant Cell · 162 Zitationen · DOI

  Suc represents the major transport form for carbohydrates in plants. Suc is loaded actively against a concentration gradient into sieve elements, which constitute the conduit for assimilate export out of leaves. Three members of the Suc transporter family with different properties were identified: SUT1, a high-affinity Suc proton cotransporter; SUT4, a low-affinity transporter; and SUT2, which in yeast is only weakly active and shows features similar to those of the yeast sugar sensors RGT2 and SNF3. Immunolocalization demonstrated that all three SUT proteins are localized in the same enucleate sieve element. Thus, the potential of Suc transporters to form homooligomers was tested by the yeast-based split-ubiquitin system. The results show that both SUT1 and SUT2 have the potential to form homooligomers. Moreover, all three Suc transporters have the potential to interact with each other. As controls, a potassium channel and a monosaccharide transporter, expressed in the plasma membrane, did not interact with the SUTs. The in vivo interaction between the functionally different Suc transporters indicates that the membrane proteins are capable of forming oligomeric structures that, like mammalian Glc transporter complexes, might be of functional significance for the regulation of transport.

• Photochemical processes, carbon assimilation and RNA accumulation of sucrose transporter genes in tomato arbuscular mycorrhiza

  2011

  Journal of Plant Physiology · 159 Zitationen · DOI

• The Sucrose Transporter <i>StSUT1</i> Localizes to Sieve Elements in Potato Tuber Phloem and Influences Tuber Physiology and Development,

  2003

  PLANT PHYSIOLOGY · 151 Zitationen · DOI

  The sucrose (Suc) H(+)-cotransporter StSUT1 from potato (Solanum tuberosum), which is essential for long-distance transport of Suc and assumed to play a role in phloem loading in mature leaves, was found to be expressed in sink tubers. To answer the question of whether SUT1 serves a function in phloem unloading in tubers, the promoter was fused to gusA and expression was analyzed in transgenic potato. SUT1 expression was unexpectedly detected not in tuber parenchyma but in the phloem of sink tubers. Immunolocalization demonstrated that StSUT1 protein was present only in sieve elements of sink tubers, cells normally involved in export of Suc from the phloem to supply developing tubers, raising the question of the role of SUT1 in tubers. SUT1 expression was inhibited by antisense in transgenic potato plants using a class I patatin promoter B33, which is primarily expressed in the phloem of developing tubers. Reduced SUT1 expression in tubers did not affect aboveground organs but led to reduced fresh weight accumulation during early stages of tuber development, indicating that in this phase SUT1 plays an important role for sugar transport. Changes in Suc- and starch-modifying enzyme activities and metabolite profiles are consistent with the developmental switch in unloading mechanisms. Altogether, the findings may suggest a role of SUT1 in retrieval of Suc from the apoplasm, thereby regulating the osmotic potential in the extracellular space, or a direct role in phloem unloading acting as a phloem exporter transferring Suc from the sieve elements into the apoplasm.

• Members of RTP and REEP Gene Families Influence Functional Bitter Taste Receptor Expression

  2006

  Journal of Biological Chemistry · 134 Zitationen · DOI

  Functional characterization of chemosensory receptors is usually achieved by heterologous expression in mammalian cell lines. However, many chemoreceptor genes, including bitter taste receptors (TAS2Rs), show only marginal cell surface expression. Usually, these problems are circumvented by using chimeric receptors consisting of "export tags" and the receptor sequence itself. It seems likely that chemoreceptor cells express factors for cell surface targeting of native receptor molecules in vivo. For TAS2Rs, however, such factors are still unknown. The present study investigates the influence of RTP and REEP proteins on the functional expression of human TAS2Rs in heterologous cells. We expressed hTAS2Rs in HEK 293T cells and observed dramatic differences in responsiveness to agonist stimulation. By immunocytochemistry we show accumulation of the bitter beta-glucopyranoside receptor hTAS2R16 in the Golgi compartment. Coexpression of RTP and REEP proteins changed the responses of some hTAS2Rs upon agonist stimulation, which is likely due to efficient cell surface localization as demonstrated by cell surface biotinylation experiments. The coimmunoprecipitation of hTAS2R16 and RTP3 or RTP4 suggests that the mechanism by which these cofactors influence hTAS2R16 function might involve direct protein-protein interaction. Finally, expression analyses demonstrate RTP and REEP gene expression in human circumvallate papillae and testis, both of which are sites of TAS2R gene expression.

• The sucrose transporter Sl<scp>SUT</scp>2 from tomato interacts with brassinosteroid functioning and affects arbuscular mycorrhiza formation

  2014

  The Plant Journal · 120 Zitationen · DOI

  Mycorrhizal plants benefit from the fungal partners by getting better access to soil nutrients. In exchange, the plant supplies carbohydrates to the fungus. The additional carbohydrate demand in mycorrhizal plants was shown to be balanced partially by higher CO2 assimilation and increased C metabolism in shoots and roots. In order to test the role of sucrose transport for fungal development in arbuscular mycorrhizal (AM) tomato, transgenic plants with down-regulated expression of three sucrose transporter genes were analysed. Plants that carried an antisense construct of SlSUT2 (SlSUT2as) repeatedly exhibited increased mycorrhizal colonization and the positive effect of plants to mycorrhiza was abolished. Grafting experiments between transgenic and wild-type rootstocks and scions indicated that mainly the root-specific function of SlSUT2 has an impact on colonization of tomato roots with the AM fungus. Localization of SISUT2 to the periarbuscular membrane indicates a role in back transport of sucrose from the periarbuscular matrix into the plant cell thereby affecting hyphal development. Screening of an expression library for SlSUT2-interacting proteins revealed interactions with candidates involved in brassinosteroid (BR) signaling or biosynthesis. Interaction of these candidates with SlSUT2 was confirmed by bimolecular fluorescence complementation. Tomato mutants defective in BR biosynthesis were analysed with respect to mycorrhizal symbiosis and showed indeed decreased mycorrhization. This finding suggests that BRs affect mycorrhizal infection and colonization. If the inhibitory effect of SlSUT2 on mycorrhizal growth involves components of BR synthesis and of the BR signaling pathway is discussed.

• A Comparison of the Sucrose Transporter Systems of Different Plant Species

  2003

  Plant Biology · 117 Zitationen · DOI

  Abstract: The sucrose uptake behaviour of many different plant species is characterised by the presence of at least two components with distinct kinetic properties. These include at least one high‐affinity and one low‐affinity transport system. All known sucrose transporters from higher plants fall into one of three large subfamilies, according to phylogenetic analysis. Apparently, the largest subfamily, the SUT1 subfamily, exclusively consists of high‐affinity sucrose transporters from dicotyledons, whereas none of the transporters from monocotyledonous plants groups within this subfamily. The other two subfamilies of sucrose transporter‐like proteins are either low‐affinity transporter or putative sucrose‐sensing proteins. Most of the known sucrose transporters from monocotyledons are closely related to the SUT2 subfamily and include high‐affinity transporters, suggesting a different evolutionary origin of dicotyledonous and monocotyledonous sucrose transporter gene families.

• Three TAS2R Bitter Taste Receptors Mediate the Psychophysical Responses to Bitter Compounds of Hops (Humulus lupulus L.) and Beer

  2009

  Chemosensory Perception · 114 Zitationen · DOI

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Name

PD Dr. rer. nat. Christina Kühn

Titel

PD Dr. rer. nat.

Fakultät

Lebenswissenschaftliche Fakultät

Institut

Institut für Biologie

Arbeitsgruppe

Pflanzenphysiologie I

Telefon

+49 30 2093-98342

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26.4.2026, 01:08:10