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Published on October 3, 2008; 10.1104/pp.108.128454

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Received August 26, 2008
Accepted September 26, 2008

Characterization of cytokinin and adenine transport in Arabidopsis cell cultures

Anna Cedzich , Harald Stransky , Burkhard Schulz , and Wolf B. Frommer *

ZMBP, University Tubingen, Auf der Morgenstelle 1, D-72071 Tubingen, Germany; Institute of Plant Physiology and Biotechnology (260), University of Hohenheim, D-70593 Stuttgart, Germany; Dept. Horticulture and Landscape Architecture; Purdue University; 625 Agriculture Mall Drive, West Lafayette, IN 47907-201, USA; Dept. Plant Biol., Carnegie Institution for Science, 260 Panama St., Stanford CA 94305, USA

* Corresponding author; email: wfrommer{at}stanford.edu.

Cytokinins are distributed through the vascular system and trigger responses of target cells via receptor-mediated signal transduction. Perception and transduction of the signal can occur at the plasma membrane or in the cytosol. The signal is terminated by the action of extra- or intracellular cytokinin oxidases. While radiotracer studies have been used to study transport and metabolism of cytokinins in plants, little is known about the kinetic properties of cytokinin transport. To provide a reference data set, radiolabeled trans-zeatin was used to for uptake studies in Arabidopsis cell culture. Uptake kinetics of trans-zeatin are multiphasic, indicating the presence of both low- and high-affinity transport systems. The protonophore CCCP is an effective inhibitor of cytokinin uptake, consistent with H+-mediated uptake. Other physiological cytokinins such as isopentenyladenine and benzylaminopurine are effective competitors of trans-zeatin uptake, whereas allantoin has no inhibitory effect. Adenine competes for zeatin uptake indicating that the degradation product of cytokinin oxidases is transported by the same systems. Comparison of adenine and trans-zeatin uptake in Arabidopsis seedlings reveals similar uptake kinetics. Kinetic properties as well as substrate specificity determined in cell cultures is compatible with the hypothesis that members of the plant-specific PUP family play a role in adenine transport for scavenging extracellular adenine, and may in addition be involved in low affinity cytokinin uptake.






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