Ribosylated forms of the plant hormones cytokinins (CKs) are the dominant CK species translocated over long distances. The irreplaceable role of root-to-shoot translocated trans-zeatin riboside in the mediation of shoot development implies the existence of a yet-uncharacterized CK riboside-specific membrane transport system. In this work, we report significant differences in the kinetics of the membrane transport of CK nucleobases and ribosides and the overall affinity of membrane-bound carriers towards the two CK forms. We further characterize the membrane transport of CK nucleobases and ribosides mediated by Arabidopsis EQULIBRATIVE NUCLEOSIDE TRANSPORTER 3 (AtENT3) in tobacco BY-2 cells. Combining experimental data with computational modelling, we show that residues Tyr61 and Asp129, which are conserved among plant ENTs but not among ENTs from other species, are necessary for CK binding and that their mutation abolishes the ability of AtENT3 to transport CKs. Finally, we show that changes in AtENT3 have different effects on the concentrations of trans-zeatin riboside throughout Arabidopsis plants and on the overall CK concentrations in roots, implying that AtENT3 participates in both the long- and the short-distance transport of CKs.

Department of Experimental Plant Biology Faculty of Science Charles University Viničná 5 Prague 128 44 Czechia

Laboratory of Functional Genomics and Proteomics National Centre for Biomolecular Research Faculty of Science Masaryk University Brno 611 37 Czechia

Laboratory of Growth Regulators Faculty of Science of Palacký University and Institute of Experimental Botany of the Czech Academy of Sciences Šlechtitelů 27 Olomouc CZ 77900 Czechia

Laboratory of Hormonal Regulations in Plants Institute of Experimental Botany of the Czech Academy of Sciences Rozvojová 263 Prague 165 00 Czechia

Mendel Centre for Plant Genomics and Proteomics Central European Institute of Technology Masaryk University Brno 625 00 Czechia

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Abraham  M, Alekseenko  A, Bergh  C, et al.  2024. GROMACS 2023.5 source code. Zenodo. 10.5281/zenodo.11104849 DOI

Abraham  MJ, Murtola  T, Schulz  R, Páll  S, Smith  JC, Hess  B, Lindahl  E. 2015. GROMACS: high performance molecular simulations through multi-level parallelism from laptops to supercomputers. SoftwareX  1–2, 19–25.

Alexander  CR, Dingman  DW, Schultes  NP, Mourad  GS. 2018. The solute transport profile of two Aza-guanine transporters from the honey bee pathogen PubMed

An  G, Watson  BD, Stachel  S, Gordon  MP, Nester  EW. 1985. New cloning vehicles for transformation of higher plants. The EMBO Journal  4, 277–284. PubMed PMC

Best  RB, Zhu  X, Shim  J, Lopes  PEM, Mittal  J, Feig  M, MacKerell  AD  Jr. 2012. Optimization of the additive CHARMM all-atom protein force field targeting improved sampling of the backbone ϕ, ψ and side-chain χ PubMed PMC

Bishopp  A, Lehesranta  S, Vatén  A, Help  H, El-Showk  S, Scheres  B, Helariutta  K, Mähönen  AP, Sakakibara  H, Helariutta  Y. 2011. Phloem-transported cytokinin regulates polar auxin transport and maintains vascular pattern in the root meristem. Current Biology  21, 927–932. PubMed

Cavari  BZ, Avi-Dor  Y, Grossowicz  N. 1967. Effect of carbonyl cyanide PubMed PMC

Chang  L, Ramireddy  E, Schmülling  T. 2015. Cytokinin as a positional cue regulating lateral root spacing in PubMed PMC

Clough  SJ, Bent  AF. 1998. Floral dip: a simplified method for PubMed

Corbesier  L, Prinsen  E, Jacqmard  A, Lejeune  P, Van Onckelen  H, Périlleux  C, Bernier  G. 2003. Cytokinin levels in leaves, leaf exudate and shoot apical meristem of PubMed

Cornelius  S, Traub  M, Bernard  C, Salzig  C, Lang  P, Möhlmann  T. 2012. Nucleoside transport across the plasma membrane mediated by equilibrative nucleoside transporter 3 influences metabolism of PubMed

Culos  D, Watanabe  M. 1983. The effect of carbonyl cyanide PubMed

Cunarro  J, Weiner  MW. 1975. Mechanism of action of agents which uncouple oxidative phosphorylation: direct correlation between protoncarrying and respiratory-releasing properties using rat liver mitochondria. Biochimica et Biophysica Acta – Bioenergetics  387, 234–240. PubMed

Curtis  MD, Grossniklaus  U. 2003. A gateway cloning vector set for high-throughput functional analysis of genes in planta. Plant Physiology  133, 462–469. PubMed PMC

Davière  J-M, Achard  P. 2013. Gibberellin signaling in plants. Development  140, 1147–1151. PubMed

De Rybel  B, Adibi  M, Breda  AS, et al.  2014. Integration of growth and patterning during vascular tissue formation in PubMed

Delbarre  A, Muller  P, Imhoff  V, Guern  J. 1996. Comparison of mechanisms controlling uptake and accumulation of 2,4-dichlorophenoxy acetic acid, naphthalene-1-acetic acid, and indole-3-acetic acid in suspension-cultured tobacco cells. Planta  198, 532–541. PubMed

Dello Ioio  R, Galinha  C, Fletcher  AG, et al.  2012. A PHABULOSA/cytokinin feedback loop controls root growth in PubMed

Dobránszki  J, Mendler-Drienyovszki  N. 2014. Cytokinin-induced changes in the chlorophyll content and fluorescence of PubMed

Dobrev  PI, Kamínek  M. 2002. Fast and efficient separation of cytokinins from auxin and abscisic acid and their purification using mixed-mode solid-phase extraction. Journal of Chromatography: A  950, 21–29. PubMed

Essmann  U, Perera  L, Berkowitz  ML, Darden  T, Lee  H, Pedersen  LG. 1995. A smooth particle mesh Ewald method. The Journal of Chemical Physics  103, 8577–8593.

Girke  C, Daumann  M, Niopek-Witz  S, Möhlmann  T. 2014. Nucleobase and nucleoside transport and integration into plant metabolism. Frontiers in Plant Science  5, 443. PubMed PMC

Goddard  TD, Huang  CC, Meng  EC, Pettersen  EF, Couch  GS, Morris  JH, Ferrin  TE. 2018. UCSF ChimeraX: meeting modern challenges in visualization and analysis. Protein Science  27, 14–25. PubMed PMC

Hess  B. 2008. P-LINCS: a parallel linear constraint solver for molecular simulation. Journal of Chemical Theory and Computation  4, 116–122. PubMed

Heytler  PG. 1963. Uncoupling of oxidative phosphorylation by carbonyl cyanide phenylhydrazones. I. Some characteristics of m-CI-CCP action on mitochondria and chloroplasts. Biochemistry  2, 357–361. PubMed

Hirose  N, Makita  N, Yamaya  T, Sakakibara  H. 2005. Functional characterization and expression analysis of a gene, PubMed PMC

Hirose  N, Takei  K, Kuroha  T, Kamada-Nobusada  T, Hayashi  H, Sakakibara  H. 2008. Regulation of cytokinin biosynthesis, compartmentalization and translocation. Journal of Experimental Botany  59, 75–83. PubMed

Hošek  P, Kubeš  M, Laňková  M, Dobrev  PI, Klíma  P, Kohoutová  M, Petrášek  J, Hoyerová  K, Jiřina  M, Zažímalová  E. 2012. Auxin transport at cellular level: new insights supported by mathematical modelling. Journal of Experimental Botany  63, 3815–3827. PubMed PMC

Hu  Y, Shani  E. 2023. Cytokinin activity—transport and homeostasis at the whole plant, cell, and subcellular levels. New Phytologist  239, 1603–1608. PubMed

Humphrey  W, Dalke  A, Schulten  K. 1996. VMD: visual molecular dynamics. Journal of Molecular Graphics  14, 33–38, 27–28. PubMed

Incarbone  M, Bradamante  G, Pruckner  F, et al.  2023. Salicylic acid and RNA interference mediate antiviral immunity of plant stem cells. Proceedings of the National Academy of Sciences, USA  120, e2302069120. PubMed PMC

Jamruszka  T, Banasiak  J, Pawela  A, et al.  2024. DOI

Jarzyniak  K, Banasiak  J, Jamruszka  T, Pawela  A, Donato  MD, Novák  O, Geisler  M, Jasiński  M. 2021. Early stages of legume–rhizobia symbiosis are controlled by ABCG-mediated transport of active cytokinins. Nature Plants  7, 428–436. PubMed

Jumper  J, Evans  R, Pritzel  A, et al.  2021. Highly accurate protein structure prediction with AlphaFold. Nature  596, 583–589. PubMed PMC

Karbanova  S, Sorf  A, Jiraskova  L, Lalinska  A, Ptackova  Z, Staud  F, Cerveny  L. 2020. PubMed

Katoh  K, Standley  DM. 2013. MAFFT multiple sequence alignment software version 7: improvements in performance and usability. Molecular Biology and Evolution  30, 772–780. PubMed PMC

Kim  A, Chen  J, Khare  D, Jin  J-Y, Yamaoka  Y, Maeshima  M, Zhao  Y, Martinoia  E, Hwang  J-U, Lee  Y. 2020. Non-intrinsic ATP-binding cassette proteins ABCI19, ABCI20 and ABCI21 modulate cytokinin response at the endoplasmic reticulum in PubMed PMC

Ko  D, Kang  J, Kiba  T, et al.  2014. PubMed PMC

Korobova  A, Kuluev  B, Möhlmann  T, Veselov  D, Kudoyarova  G. 2021. Limitation of cytokinin export to the shoots by nucleoside transporter ENT3 and its linkage with root elongation in Arabidopsis. Cells  10, 350. PubMed PMC

Králová  M, Kubalová  I, Hajný  J, et al.  2024. A decoy receptor derived from alternative splicing fine-tunes cytokinin signaling in PubMed

Landrein  B, Formosa-Jordan  P, Malivert  A, Schuster  C, Melnyk  CW, Yang  W, Turnbull  C, Meyerowitz  EM, Locke  JCW, Jönsson  H. 2018. Nitrate modulates stem cell dynamics in PubMed PMC

Laskowski  RA, Swindells  MB. 2011. LigPlot+: multiple ligand–protein interaction diagrams for drug discovery. Journal of Chemical Information and Modeling  51, 2778–2786. PubMed

Leibfried  A, To  JPC, Busch  W, Stehling  S, Kehle  A, Demar  M, Kieber  JJ, Lohmann  JU. 2005. WUSCHEL controls meristem function by direct regulation of cytokinin-inducible response regulators. Nature  438, 1172–1175. PubMed

Lemkul  J. 2019. From proteins to perturbed hamiltonians: a suite of tutorials for the GROMACS-2018 molecular simulation package [article v1.0]. Living Journal of Computational Molecular Science  1, 5068.

Li  G, Liu  K, Baldwin  SA, Wang  D. 2003. Equilibrative nucleoside transporters of PubMed

Liao  P-S, Chen  T-S, Chung  P-C. 2001. A fast algorithm for multilevel thresholding. Journal of Information Science and Engineering  17, 713–727.

Lomin  SN, Krivosheev  DM, Steklov  MY, Arkhipov  DV, Osolodkin  DI, Schmülling  T, Romanov  GA. 2015. Plant membrane assays with cytokinin receptors underpin the unique role of free cytokinin bases as biologically active ligands. Journal of Experimental Botany  66, 1851–1863. PubMed PMC

Lopes  FL, Galvan-Ampudia  C, Landrein  B. 2021. WUSCHEL in the shoot apical meristem: old player, new tricks. Journal of Experimental Botany  72, 1527–1535. PubMed

Ma  Y, Miotk  A, Šutiković  Z, et al.  2019. WUSCHEL acts as an auxin response rheostat to maintain apical stem cells in PubMed PMC

Mähönen  AP, Bishopp  A, Higuchi  M, Nieminen  KM, Kinoshita  K, Törmäkangas  K, Ikeda  Y, Oka  A, Kakimoto  T, Helariutta  Y. 2006. Cytokinin signaling and its inhibitor AHP6 regulate cell fate during vascular development. Science  311, 94–98. PubMed

Mandel  T, Candela  H, Landau  U, Asis  L, Zilinger  E, Carles  CC, Williams  LE. 2016. Differential regulation of meristem size, morphology and organization by the ERECTA, CLAVATA and class III HD-ZIP pathways. Development  143, 1612–1622. PubMed PMC

Michniewicz  M, Frick  EM, Strader  LC. 2015. Gateway-compatible tissue-specific vectors for plant transformation. BMC Research Notes  8, 63. PubMed PMC

Miller  CO, Skoog  F, Okumura  FS, von Saltza  MH, Strong  FM. 1956. Isolation, structure and synthesis of kinetin, a substance promoting cell division. Journal of the American Chemical Society  78, 1375–1380.

Miyamoto  S, Kollman  PA. 1992. Settle: an analytical version of the SHAKE and RATTLE algorithm for rigid water models. Journal of Computational Chemistry  13, 952–962.

Möhlmann  T, Mezher  Z, Schwerdtfeger  G, Neuhaus  HE. 2001. Characterisation of a concentrative type of adenosine transporter from PubMed

Müller  K, Dobrev  PI, Pěnčík  A, et al.  2021. DIOXYGENASE FOR AUXIN OXIDATION 1 catalyzes the oxidation of IAA amino acid conjugates. Plant Physiology  187, 103–115. PubMed PMC

Nagata  T, Nemoto  Y, Hasezawa  S. 1992. Tobacco BY-2 cell line as the “HeLa” cell in the cell biology of higher plants. International Review of Cytology  132, 1–30.

Nedvěd  D, Hošek  P, Klíma  P, Hoyerová  K. 2021. Differential subcellular distribution of cytokinins: how does membrane transport fit into the big picture?  International Journal of Molecular Sciences  22, 3428. PubMed PMC

Nedvěd  D, Hudeček  M, Klíma  P, Lacek  J, Müller  K, Kuchařová  A, Hošek  P, Šmeringai  J, Pernisová  M, Motyka  V, Plíhal  O, Hoyerová  K. 2025. Data from ‘Membrane transport of root-borne trans-zeatin riboside maintains the cytokinin homeostasis in shoots’. Zenodo, 10.5281/zenodo.16568211. PubMed DOI PMC

Newell  DR, O’Connor  PM, Hilary Calvert  A, Harrap  KR. 1986. The effect of the nucleoside transport inhibitor dipyridamole on the incorporation of [ PubMed

Osugi  A, Kojima  M, Takebayashi  Y, Ueda  N, Kiba  T, Sakakibara  H. 2017. Systemic transport of PubMed

Páll  S, Abraham  MJ, Kutzner  C, Hess  B, Lindahl  E. 2015. Tackling exascale software challenges in molecular dynamics simulations with GROMACS. In: Markidis  S, Laure  E, eds. Solving software challenges for exascale. Cham: Springer International Publishing, 3–27.

Paul  A, Laurila  T, Vuorinen  V, Divinski  SV. 2014. Fick’s laws of diffusion. In: Paul  A, Laurila  T, Vuorinen  V, Divinski  SV, eds. Thermodynamics, diffusion and the Kirkendall effect in solids. Cham: Springer International Publishing, 115–139.

Pei  J, Grishin  NV. 2001. AL2CO: calculation of positional conservation in a protein sequence alignment. Bioinformatics 17, 700–712. PubMed

Qi  Z, Xiong  L. 2013. Characterization of a purine permease family gene PubMed

Radchuk  V, Belew  ZM, Gündel  A, et al.  2023. SWEET11b transports both sugar and cytokinin in developing barley grains. The Plant Cell  35, 2186–2207. PubMed PMC

Ravindranath  PA, Forli  S, Goodsell  DS, Olson  AJ, Sanner  MF. 2015. AutoDockFR: advances in protein-ligand docking with explicitly specified binding site flexibility. PLoS Computational Biology  11, e1004586. PubMed PMC

Richmond  AE, Lang  A. 1957. Effect of kinetin on protein content and survival of detached

Riefler  M, Novak  O, Strnad  M, Schmülling  T. 2006. PubMed PMC

Rong  C, Zhang  R, Liu  Y, Chang  Z, Liu  Z, Ding  Y, Ding  C. 2024. Purine permease (PUP) family gene PUP11 positively regulates the rice seed setting rate by influencing seed development. Plant Cell Reports  43, 112. PubMed

Sakakibara  H. 2021. Cytokinin biosynthesis and transport for systemic nitrogen signaling. The Plant Journal  105, 421–430. PubMed

Schaller  GE, Street  IH, Kieber  JJ. 2014. Cytokinin and the cell cycle. Current Opinion in Plant Biology  21, 7–15. PubMed

Schrödinger, LLC. 2015. The PyMOL molecular graphics system, Version 1.8.

Silva-Navas  J, Moreno-Risueno  MA, Manzano  C, Pallero-Baena  M, Navarro-Neila  S, Téllez-Robledo  B, Garcia-Mina  JM, Baigorri  R, Gallego  FJ, del Pozo  JC. 2015. D-Root: a system for cultivating plants with the roots in darkness or under different light conditions. The Plant Journal  84, 244–255. PubMed

Skoog  F, Miller  CO. 1957. Chemical regulation of growth and organ formation in plant tissues cultured in vitro. Symposia of the Society for Experimental Biology  11, 118–130. PubMed

Šmeringai  J, Rudolf  J, Trtílek  M, Procházková Schrumpfová  P, Pernisová  M. 2023. Shoot phenotyping of cytokinin receptors mutants revealed fluorescence parameters as early markers of drought stress. bioRxiv. 10.1101/2023.11.30.569457. [Preprint]. DOI

Stoffer-Bittner  AJ, Alexander  CR, Dingman  DW, Mourad  GS, Schultes  NP. 2018. Functional characterization of the uracil transporter from honeybee pathogen PubMed

Sun  J, Hirose  N, Wang  X, Wen  P, Xue  L, Sakakibara  H, Zuo  J. 2005.

Takei  K, Sakakibara  H, Taniguchi  M, Sugiyama  T. 2001. Nitrogen-dependent accumulation of cytokinins in root and the translocation to leaf: implication of cytokinin species that induces gene expression of maize response regulator. Plant & Cell Physiology  42, 85–93. PubMed

Talla  SK, Panigrahy  M, Kappara  S, Nirosha  P, Neelamraju  S, Ramanan  R. 2016. Cytokinin delays dark-induced senescence in rice by maintaining the chlorophyll cycle and photosynthetic complexes. Journal of Experimental Botany  67, 1839–1851. PubMed PMC

Tessi  TM, Brumm  S, Winklbauer  E, et al.  2021. Arabidopsis AZG2 transports cytokinins PubMed

Tessi  TM, Maurino  VG, Shahriari  M, et al.  2023. AZG1 is a cytokinin transporter that interacts with auxin transporter PIN1 and regulates the root stress response. New Phytologist  238, 1924–1941. PubMed

The GIMP Team . 2024. GNU image manipulation program.

The UniProt Consortium . 2023. UniProt: the universal protein knowledgebase in 2023. Nucleic Acids Research  51, D523–D531. PubMed PMC

To  JPC, Deruère  J, Maxwell  BB, Morris  VF, Hutchison  CE, Ferreira  FJ, Schaller  GE, Kieber  JJ. 2007. Cytokinin regulates type-A PubMed PMC

To  JPC, Haberer  G, Ferreira  FJ, Deruère  J, Mason  MG, Schaller  GE, Alonso  JM, Ecker  JR, Kieber  JJ. 2004. Type-A Arabidopsis response regulators are partially redundant negative regulators of cytokinin signaling. The Plant Cell  16, 658–671. PubMed PMC

Traub  M, Flörchinger  M, Piecuch  J, Kunz  H, Weise-Steinmetz  A, Deitmer Joachim  W, Ekkehard Neuhaus  H, Möhlmann  T. 2007. The fluorouridine insensitive 1 ( PubMed

van der Walt  SJ, Schönberger  JL, Nunez-Iglesias  J, Boulogne  F, Warner  JD, Yager  N, Gouillart  E, Yu  T. 2014. scikit-image: image processing in Python. PeerJ  2, e453. PubMed PMC

Vanommeslaeghe  K, MacKerell  AD  Jr. 2012. Automation of the CHARMM general force field (CGenFF) I: bond perception and atom typing. Journal of Chemical Information and Modeling  52, 3144–3154. PubMed PMC

Vanommeslaeghe  K, Raman  EP, MacKerell  AD  Jr. 2012. Automation of the CHARMM general force field (CGenFF) II: assignment of bonded parameters and partial atomic charges. Journal of Chemical Information and Modeling  52, 3155–3168. PubMed PMC

Virtanen  P, Gommers  R, Oliphant  TE, et al.  2020. Scipy 1.0: fundamental algorithms for scientific computing in Python. Nature Methods  17, 261–272. PubMed PMC

Wang  C, Yu  L, Zhang  J, et al.  2023. Structural basis of the substrate recognition and inhibition mechanism of PubMed PMC

Ward  JL, Sherali  A, Mo  Z-P, Tse  C-M. 2000. Kinetic and pharmacological properties of cloned human equilibrative nucleoside transporters, ENT1 and ENT2, stably expressed in nucleoside transporter-deficient PK15 cells: ENT2 EXHIBITS A LOW AFFINITY FOR GUANOSINE AND CYTIDINE BUT A HIGH AFFINITY FOR INOSINE. The Journal of Biological Chemistry  275, 8375–8381. PubMed

Waterhouse  AM, Procter  JB, Martin  DMA, Clamp  M, Barton  GJ. 2009. Jalview version 2—a multiple sequence alignment editor and analysis workbench. Bioinformatics  25, 1189–1191. PubMed PMC

Werner  T, Motyka  V, Laucou  V, Smets  R, Van Onckelen  H, Schmülling  T. 2003. Cytokinin-deficient transgenic Arabidopsis plants show multiple developmental alterations indicating opposite functions of cytokinins in the regulation of shoot and root meristem activity. The Plant Cell  15, 2532–2550. PubMed PMC

Werner  T, Motyka  V, Strnad  M, Schmülling  T. 2001. Regulation of plant growth by cytokinin. Proceedings of the National Academy of Sciences, USA  98, 10487–10492. PubMed PMC

Woffendin  C, Plagemann  PGW. 1987. Interaction of [ PubMed

Wormit  A, Traub  M, Flörchinger  M, Neuhaus  HE, Möhlmann  T. 2004. Characterization of three novel members of the PubMed PMC

Wright  NJ, Lee  S-Y. 2019. Structures of human ENT1 in complex with adenosine reuptake inhibitors. Nature Structural & Molecular Biology  26, 599–606. PubMed PMC

Wybouw  B, De Rybel  B. 2019. Cytokinin—a developing story. Trends in Plant Science  24, 177–185. PubMed

Xiao  Y, Liu  D, Zhang  G, Gao  S, Liu  L, Xu  F, Che  R, Wang  Y, Tong  H, Chu  C. 2019. PubMed

Xiao  Y, Zhang  J, Yu  G, et al.  2020. Endoplasmic reticulum-localized PURINE PERMEASE1 regulates plant height and grain weight by modulating cytokinin distribution in rice. Frontiers in Plant Science  11, 618560. PubMed PMC

Yang  Q, Zhang  J, Kojima  M, Takebayashi  Y, Uragami  T, Kiba  T, Sakakibara  H, Lee  Y. 2022. ABCG11 modulates cytokinin responses in PubMed PMC

Yang  W, Cortijo  S, Korsbo  N, Roszak  P, Schiessl  K, Gurzadyan  A, Wightman  R, Jönsson  H, Meyerowitz  E. 2021. Molecular mechanism of cytokinin-activated cell division in PubMed PMC

Yao  SYM, Ng  AML, Cass  CE, Baldwin  SA, Young  JD. 2011. Nucleobase transport by human equilibrative nucleoside transporter 1 (hENT1). The Journal of Biological Chemistry  286, 32552–32562. PubMed PMC

Zhang  K, Novak  O, Wei  Z, Gou  M, Zhang  X, Yu  Y, Yang  H, Cai  Y, Strnad  M, Liu  C-J. 2014. PubMed

Zhao  J, Yu  N, Ju  M, Fan  B, Zhang  Y, Zhu  E, Zhang  M, Zhang  K. 2019. ABC transporter OsABCG18 controls the shootward transport of cytokinins and grain yield in rice. Journal of Experimental Botany  70, 6277–6291. PubMed PMC

Zhao  J, Deng  X, Qian  J, et al.  2023. PubMed PMC

Zhao  Y, Stoffler  D, Sanner  M. 2006. Hierarchical and multi-resolution representation of protein flexibility. Bioinformatics  22, 2768–2774. PubMed

Zürcher  E, Liu  J, di Donato  M, Geisler  M, Müller  B. 2016. Plant development regulated by cytokinin sinks. Science  353, 1027–1030. PubMed

Membrane transport of root-borne trans-zeatin riboside maintains the cytokinin homeostasis in shoots