Biochimie et Physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes, UMR 5004 CNRS/UMR 0386 INRA/Montpellier SupAgro/Université Montpellier 2, F-34060 Montpellier cedex 1, France.
Plant Physiol. 2010 Mar;152(3):1418-30. doi: 10.1104/pp.109.145326. Epub 2009 Dec 24.
Aquaporins are channel proteins that facilitate the transport of water across plant cell membranes. In this work, we used a combination of pharmacological and reverse genetic approaches to investigate the overall significance of aquaporins for tissue water conductivity in Arabidopsis (Arabidopsis thaliana). We addressed the function in roots and leaves of AtPIP1;2, one of the most abundantly expressed isoforms of the plasma membrane intrinsic protein family. At variance with the water transport phenotype previously described in AtPIP2;2 knockout mutants, disruption of AtPIP1;2 reduced by 20% to 30% the root hydrostatic hydraulic conductivity but did not modify osmotic root water transport. These results document qualitatively distinct functions of different PIP isoforms in root water uptake. The hydraulic conductivity of excised rosettes (K(ros)) was measured by a novel pressure chamber technique. Exposure of Arabidopsis plants to darkness increased K(ros) by up to 90%. Mercury and azide, two aquaporin inhibitors with distinct modes of action, were able to induce similar inhibition of K(ros) by approximately 13% and approximately 25% in rosettes from plants grown in the light or under prolonged (11-18 h) darkness, respectively. Prolonged darkness enhanced the transcript abundance of several PIP genes, including AtPIP1;2. Mutant analysis showed that, under prolonged darkness conditions, AtPIP1;2 can contribute to up to approximately 20% of K(ros) and to the osmotic water permeability of isolated mesophyll protoplasts. Therefore, AtPIP1;2 can account for a significant portion of aquaporin-mediated leaf water transport. The overall work shows that AtPIP1;2 represents a key component of whole-plant hydraulics.
水通道蛋白是促进植物细胞膜上水运输的通道蛋白。在这项工作中，我们使用药理学和反向遗传学方法的组合来研究水通道蛋白对拟南芥（Arabidopsis thaliana）组织水导率的整体意义。我们研究了质膜内在蛋白家族中表达最丰富的同工型之一 AtPIP1;2 在根和叶中的功能。与先前在 AtPIP2;2 敲除突变体中描述的水运输表型不同，AtPIP1;2 的破坏使根静水液压导率降低了 20%至 30%，但不改变渗透根水运输。这些结果证明了不同 PIP 同工型在根水吸收中具有定性不同的功能。通过一种新的压力室技术测量离体花环（K(ros)）的水力传导性。将拟南芥植物暴露在黑暗中可使 K(ros)增加高达 90%。汞和叠氮化物是两种具有不同作用模式的水通道蛋白抑制剂，能够在光照下或在延长（11-18 小时）黑暗中生长的植物的离体花环中分别诱导约 13%和约 25%的 K(ros)相似抑制。延长黑暗时间增强了包括 AtPIP1;2 在内的几个 PIP 基因的转录丰度。突变体分析表明，在延长的黑暗条件下，AtPIP1;2 可以贡献高达约 20%的 K(ros)和分离的叶肉原生质体的渗透水通透性。因此，AtPIP1;2 可以解释叶片水运输的重要部分。总的来说，这项工作表明 AtPIP1;2 是整个植物水力学的关键组成部分。
