Kühn C, Franceschi V R, Schulz A, Lemoine R, Frommer W B
Institut für Botanik, Eberhard-Karls-Universität, Auf der Morgenstelle 1, D-72076 Tübingen, Germany.
Science. 1997 Feb 28;275(5304):1298-300. doi: 10.1126/science.275.5304.1298.
The leaf sucrose transporter SUT1 is essential for phloem loading and long-distance transport of assimilates. Both SUT1 messenger RNA (mRNA) and protein were shown to be diurnally regulated and to have high turnover rates. SUT1 protein was detected by immunolocalization in plasma membranes of enucleate sieve elements (SEs) in tobacco, potato, and tomato. Analysis by in situ hybridization showed that SUT1 mRNA localizes mainly to the SE and is preferentially associated with plasmodesmata. Antisense inhibition of SUT1 expression under control of a companion cell (CC)-specific promoter indicated synthesis of SUT1 mRNA in the CC. These results provide evidence for targeting of plant endogenous mRNA and potentially SUT1 protein through phloem plasmodesmata and for sucrose loading at the plasma membrane of SE.
叶片蔗糖转运蛋白SUT1对于韧皮部装载和同化物的长距离运输至关重要。SUT1信使核糖核酸（mRNA）和蛋白质均表现出昼夜调节且周转率很高。通过免疫定位在烟草、马铃薯和番茄的无核筛管分子（SEs）的质膜中检测到了SUT1蛋白。原位杂交分析表明，SUT1 mRNA主要定位于筛管分子，并且优先与胞间连丝相关。在伴胞（CC）特异性启动子控制下对SUT1表达进行反义抑制表明，SUT1 mRNA在伴胞中合成。这些结果为植物内源性mRNA以及潜在的SUT1蛋白通过韧皮部胞间连丝的靶向运输以及在筛管分子质膜上的蔗糖装载提供了证据。
