Under anaerobic stress Arabidopsis thaliana induces the expression of a collection of core hypoxia genes that encode proteins associated with an adaptive response. Included in these core hypoxia genes is NIP2;1, which encodes a member of the "Nodulin-like Intrinsic Protein" (NIP) subgroup of the aquaporin superfamily of membrane channel proteins. Under normal growth, NIP2;1 expression is limited to the "anoxia core" region of the root stele, but shows substantial induction in response to low oxygen stress (as high as 1000-fold by 2-4 hr of hypoxia challenge), and accumulates in all root tissues. During hypoxia, NIP2;1-GFP, accumulates on the cell surface by 2 hr and then is distributed between the cell surface and internal membranes during sustained hypoxia, and remains elevated in root tissues through 4 hrs of reoxygenation recovery. T-DNA insertional mutant nip2;1 plants show elevation of lactic acid within root tissues, and a reduced efflux of lactic acid and acidification of the external medium. Together with previous biochemical evidence demonstrating that NIP2;1 has lactic acid permease activity, the present work supports the hypothesis that the protein facilitates the release of cellular lactate to the rhizosphere to prevent lactic acid toxicity. In support of this, nip2;1 plants show poorer survival to argon-induced hypoxia stress. Nip2;1 mutant plants also show elevated expression of ethanolic fermentation transcripts, as well as reduced expression the lactate metabolic enzyme GOX3, suggesting that the altered efflux of lactate through NIP2;1 regulates other pyruvate and lactate metabolism pathways.

中文翻译：

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拟南芥NIP2; 1乳酸通道促进低氧胁迫下的植物存活

在厌氧胁迫下，拟南芥诱导表达一系列核心缺氧基因的表达，这些基因编码与适应性反应相关的蛋白质。这些核心的缺氧基因中包括NIP2; 1，它编码膜通道蛋白水通道蛋白超家族的“结节蛋白样内在蛋白”（NIP）亚组的成员。在正常生长下，NIP2; 1的表达仅限于根碑的“缺氧核心”区域，但在对低氧胁迫（缺氧激发2-4小时时高达1000倍）的响应中显示出明显的诱导作用，并且在所有根组织中积累。在缺氧期间，NIP2; 1-GFP会在2小时内积聚在细胞表面，然后在持续缺氧期间分布在细胞表面和内膜之间，并在恢复氧合4小时后在根组织中保持升高。T-DNA插入突变体nip2; 1植物显示出根组织内乳酸的升高，乳酸的流出减少和外部介质的酸化。连同先前的生物化学证据表明NIP2; 1具有乳酸通透酶活性，目前的工作支持以下假设：蛋白质可促进细胞乳酸向根际的释放，从而防止乳酸毒性。为此，nip2; 1植物在氩气诱导的缺氧胁迫下的存活期较差。Nip2; 1突变植物还显示出乙醇发酵转录物的表达升高，以及乳酸代谢酶GOX3的表达降低，这表明乳酸通过NIP2的流出改变了。