Phloem-localized, proton-coupled sucrose carrier ZmSUT1 mediates sucrose efflux under the control of the sucrose gradient and the proton motive force
Phloem-localized, proton-coupled sucrose carrier ZmSUT1 mediates sucrose efflux under the control of the sucrose gradient and the proton motive force
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DOI：
10.1074/jbc.m501785200
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发表时间：
2005-06-03
影响因子：
4.8
通讯作者：
Hedrich, R
中科院分区：
文献类型：
--
作者：
Carpaneto, A;Geiger, D;Hedrich, R
韧皮部网络对植物至关重要，就像对人类的血管系统一样。该网络由核和无液泡互连的活细胞组装而成，代表了养分和信息的长距离传输途径。根据蒙克假设，诸如蔗糖之类的渗透压产生了静水压力，该静水压力驱动了源和水槽韧皮部之间的养分和水流动（Munch，E。（1930）Der Pflanze，Gustav Fischer，Jena，Dermany，Die Stoffbewegungen。尽管质子偶联的蔗糖载体已定位在筛子和源和水槽组织的伴随细胞质膜，对分子代表的知识以及蔗糖韧皮部外排的机制仍然很少。我们在异爪蟾卵母细胞中表达了玉米蔗糖/质子分类蛋白的Zmsut1，并通过电生理方法研究了载体的传输特性。使用巨大的内而外贴片模式下的贴片夹技术，我们改变了蔗糖载体上的化学和电化学梯度，并分析了质子通量产生的电流。因此，我们可以证明ZMSUT1能够将蔗糖吸收到成熟的叶子中（来源）以及从韧皮部血管中解吸到异养组织（水槽）的糖。正如完美的分子机所预测的那样，ZMSUT1介导的糖耦合质子电流是可逆的，取决于蔗糖和pH梯度的方向以及整个转运蛋白的膜电位。
The phloem network is as essential for plants as the vascular system is for humans. This network, assembled by nucleus- and vacuole- free interconnected living cells, represents a long distance transport pathway for nutrients and information. According to the Munch hypothesis, osmolytes such as sucrose generate the hydrostatic pressure that drives nutrient and water flow between the source and the sink phloem (Munch, E. (1930) Die Stoffbewegungen in der Pflanze, Gustav Fischer, Jena, Germany). Although proton-coupled sucrose carriers have been localized to the sieve tube and the companion cell plasma membrane of both source and sink tissues, knowledge of the molecular representatives and the mechanism of the sucrose phloem efflux is still scant. We expressed ZmSUT1, a maize sucrose/ proton symporter, in Xenopus oocytes and studied the transport characteristics of the carrier by electrophysiological methods. Using the patch clamp techniques in the giant inside-out patch mode, we altered the chemical and electrochemical gradient across the sucrose carrier and analyzed the currents generated by the proton flux. Thereby we could show that ZmSUT1 is capable of mediating both the sucrose uptake into the phloem in mature leaves ( source) as well as the desorption of sugar from the phloem vessels into heterotrophic tissues ( sink). As predicted from a perfect molecular machine, the ZmSUT1-mediated sucrose-coupled proton current was reversible and depended on the direction of the sucrose and pH gradient as well as the membrane potential across the transporter.