Characterization, localization, and seasonal changes of the sucrose transporter FeSUT1 in the phloem of Fraxinus excelsior
Oener-Sieben S, Rappl C, Sauer N, Stadler R, Lohaus G (2015)
Publication Status: Published
Publication Type: Journal article, Original article
Publication year: 2015
Journal
Book Volume: 66
Pages Range: 4807-4819
Journal Issue: 15
DOI: 10.1093/jxb/erv255
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. excelsior was analysed. Heterologous expression in baker's yeast showed that FeSUT1 mediates the uptake of sucrose. Immunohistochemical analyses revealed that FeSUT1 was exclusively located in phloem cells of minor veins and in the transport phloem of F. excelsior. Further characterization identified these cells as sieve elements and possibly ordinary companion cells but not as intermediary cells. The localization and expression pattern point towards functions of FeSUT1 in phloem loading of sucrose as well as in sucrose retrieval. FeSUT1 is most likely responsible for the observed sucrose gradient between mesophyll and phloem. The elevated expression level of FeSUT1 indicated an increased apoplastic carbon export activity from the leaves during spring and late autumn. It is hypothesized that the importance of apoplastic loading is high under low-sucrose conditions and that the availability of two different phloem-loading mechanisms confers advantages for temperate woody species like F. excelsior.
Authors with CRIS profile
Norbert Sauer
Lehrstuhl für Molekulare Pflanzenphysiologie
Ruth Stadler
Lehrstuhl für Molekulare Pflanzenphysiologie
Involved external institutions
Germany (DE)How to cite
APA:
Oener-Sieben, S., Rappl, C., Sauer, N., Stadler, R., & Lohaus, G. (2015). Characterization, localization, and seasonal changes of the sucrose transporter FeSUT1 in the phloem of Fraxinus excelsior. Journal of Experimental Botany, 66(15), 4807-4819. https://doi.org/10.1093/jxb/erv255
MLA:
Oener-Sieben, Soner, et al. "Characterization, localization, and seasonal changes of the sucrose transporter FeSUT1 in the phloem of Fraxinus excelsior." Journal of Experimental Botany 66.15 (2015): 4807-4819.
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