Journal of Experimental Botany, Vol. 66, No. 15 pp. 4807–4819, 2015 doi:10.1093/jxb/erv255 Advance Access publication 28 May 2015 This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details) RESEARCH PAPER Characterization, localization, and seasonal changes of the sucrose transporter FeSUT1 in the phloem of Fraxinus Downloaded from excelsior Soner Öner-Sieben1,†, Christine Rappl2,†, Norbert Sauer2, Ruth Stadler2,‡ and Gertrud Lohaus1,‡,* 1 Molekulare Pflanzenforschung/Pflanzenbiochemie (Botanik), Bergische Universität Wuppertal, Gaußstraße 20, D-42119 Wuppertal, Germany http://jxb.oxfordjournals.org/ 2 Lehrstuhl Molekulare Pflanzenphysiologie Department Biologie, Universität Erlangen-Nürnberg, Staudtstrasse 5, D-91058 Erlangen, Germany * To whom correspondence should be addressed. E-mail:
[email protected] † These authors contributed equally to this work. ‡ These authors contributed equally to this work. Received 6 February 2015; Revised 27 March 2015; Accepted 1 May 2015 at Universitaet Erlangen-Nuernberg, Wirtschafts- und Sozialwissenschaftliche Z on August 15, 2016 Editor: Jeremy Pritchard Abstract Trees are generally assumed to be symplastic phloem loaders. A typical feature for most wooden species is an open minor vein structure with symplastic connections between mesophyll cells and phloem cells, which allow sucrose to move cell-to-cell through the plasmodesmata into the phloem. Fraxinus excelsior (Oleaceae) also translocates raffinose family oligosaccharides in addition to sucrose. Sucrose concentration was recently shown to be higher in the phloem sap than in the mesophyll cells. This suggests the involvement of apoplastic steps and the activity of sucrose transporters in addition to symplastic phloem-loading processes. In this study, the sucrose transporter FeSUT1 from F.