DeWitt N D, Harper J F, Sussman M R
Department of Horticulture, University of Wisconsin, Madison 53706.
Plant J. 1991 Jul;1(1):121-8. doi: 10.1111/j.1365-313x.1991.00121.x.
Metabolic energy is required for the loading of sucrose into the phloem and translocation of sugars throughout the plant. The proton electrochemical gradient generated by a plasma membrane proton pump (H(+)-ATPase) is thought to provide energy for these processes. The plasma membrane H(+)-ATPase is encoded by a multigene family in Arabidopsis thaliana. Here we characterize the expression of isoform AHA3 (Arabidopsis H(+)-ATPase isoform 3). The AHA3 mRNA start site was mapped and 464 bp of the putative upstream regulatory region sequenced. A translational fusion of AHA3 to the beta-glucuronidase (GUS) reporter gene was constructed and used to generate transgenic Nicotiana and Arabidopsis plants. Using a histochemical stain, expression of the AHA3/GUS fusion was found predominantly in phloem cells of leaves, stems, roots, and flowers. Biochemical measurements of GUS activity in pith and vascular explants confirmed the histochemical localization. Our results support the hypothesis that a proton pump is present in phloem cells, possibly providing energy to drive plasma membrane cotransport systems required for phloem loading and translocation of photosynthates. In addition to AHA3/GUS expression in phloem, expression was observed in pollen and regions of the ovule, tissues whose physiological functions correlate with a requirement for high levels of solute transport.
将蔗糖装载到韧皮部以及糖类在整个植物体内的转运都需要代谢能量。质膜质子泵（H(+)-ATP酶）产生的质子电化学梯度被认为可为这些过程提供能量。拟南芥中的质膜H(+)-ATP酶由一个多基因家族编码。在此，我们对亚型AHA3（拟南芥H(+)-ATP酶亚型3）的表达进行了表征。确定了AHA3 mRNA的起始位点，并对推定的上游调控区域的464 bp进行了测序。构建了AHA3与β-葡萄糖醛酸酶（GUS）报告基因的翻译融合体，并用于培育转基因烟草和拟南芥植株。通过组织化学染色发现，AHA3/GUS融合体的表达主要出现在叶、茎、根和花的韧皮部细胞中。对髓和维管外植体中GUS活性的生化测定证实了组织化学定位。我们的结果支持以下假说：韧皮部细胞中存在质子泵，可能为驱动韧皮部装载和光合产物转运所需的质膜共转运系统提供能量。除了在韧皮部中表达AHA3/GUS外，在花粉和胚珠区域也观察到了表达，这些组织的生理功能与高水平溶质转运的需求相关。
