Australian Centre for Plant Functional Genomics, Glen Osmond, South Australia 5064, Australia.
Plant Physiol. 2010 Mar;152(3):1431-41. doi: 10.1104/pp.109.152009. Epub 2010 Jan 6.
Remobilization of inorganic phosphate (P(i)) within a plant is critical for sustaining growth and seed production under external P(i) fluctuation. The barley (Hordeum vulgare) transporter HvPHT1;6 has been implicated in P(i) remobilization. In this report, we expressed HvPHT1;6 in Xenopus laevis oocytes, allowing detailed characterization of voltage-dependent fluxes and currents induced by HvPHT1;6. HvPHT1;6 increased efflux of P(i) near oocyte resting membrane potentials, dependent on external P(i) concentration. Time-dependent inward currents were observed when membrane potentials were more negative than -160 mV, which was consistent with nH(+):HPO(4)(2-) (n > 2) cotransport, based on simultaneous radiotracer and oocyte voltage clamping, dependent upon P(i) concentration gradient and pH. Time- and voltage-dependent inward currents through HvPHT1;6 were also observed for SO(4)(2-)and to a lesser degree for NO(3)(-)Cl(-)but not for malate. Inward and outward currents showed linear dependence on the concentration of external HPO(4)(2-)similar to low-affinity P(i) transport in plant studies. The electrophysiological properties of HvPHT1;6, which locates to the plasma membrane when expressed in onion (Allium cepa) epidermal cells, are consistent with its suggested role in the remobilization of P(i) in barley plants.
植物体内无机磷酸盐（P(i)）的再移动对于在外部 P(i)波动下维持生长和种子生产至关重要。大麦（Hordeum vulgare）转运蛋白 HvPHT1;6 被认为参与了 P(i)的再移动。在本报告中，我们在非洲爪蟾卵母细胞中表达了 HvPHT1;6，从而能够详细描述 HvPHT1;6 诱导的电压依赖性通量和电流。HvPHT1;6 在接近卵母细胞静息膜电位时增加了 P(i)的外排，这依赖于外部 P(i)浓度。当膜电位比-160 mV 更负时，观察到时间依赖性内向电流，这与 nH(+):HPO(4)(2-)（n > 2）共转运一致，基于同时的放射性示踪和卵母细胞电压钳位，依赖于 P(i)浓度梯度和 pH。通过 HvPHT1;6 也观察到时间和电压依赖性内向电流对于 SO(4)(2-)，并且对于 NO(3)(-)Cl(-)但不是对于苹果酸的程度较小。内向和外向电流对外界 HPO(4)(2-)浓度表现出线性依赖性，类似于植物研究中低亲和力 P(i)转运。当在洋葱（Allium cepa）表皮细胞中表达时，HvPHT1;6 的电生理特性与其在大麦植物中 P(i)再移动的建议作用一致。
