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CELL BIOLOGY AND SIGNAL TRANSDUCTION

Immunolocalization of Solanaceous SUT1 Proteins in Companion Cells and Xylem Parenchyma: New Perspectives for Phloem Loading and Transport^1,[W],[OA]

Molekulare Pflanzenphysiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, D–91058 Erlangen, Germany

Leaf sucrose (Suc) transporters are essential for phloem loading and long-distance partitioning of assimilates in plants that load their phloem from the apoplast. Suc loading into the phloem is indispensable for the generation of the osmotic potential difference that drives phloem bulk flow and is central for the long-distance movement of phloem sap compounds, including hormones and signaling molecules. In previous analyses, solanaceous SUT1 Suc transporters from tobacco (Nicotiana tabacum), potato (Solanum tuberosum), and tomato (Solanum lycopersicum) were immunolocalized in plasma membranes of enucleate sieve elements. Here, we present data that identify solanaceous SUT1 proteins with high specificity in phloem companion cells. Moreover, comparisons of SUT1 localization in the abaxial and adaxial phloem revealed higher levels of SUT1 protein in the abaxial phloem of all three solanaceous species, suggesting different physiological roles for these two types of phloem. Finally, SUT1 proteins were identified in files of xylem parenchyma cells, mainly in the bicollateral veins. Together, our data provide new insight into the role of SUT1 proteins in solanaceous species.

² These authors contributed equally to the article.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Norbert Sauer (nsauer{at}biologie.uni-erlangen.de).

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.108.120410

^* Corresponding author; e-mail nsauer{at}biologie.uni-erlangen.de.

Received April 4, 2008; accepted June 22, 2008; published July 9, 2008.