Department of Renewable Resources, University of Alberta, 442 Earth Sciences Bldg., Edmonton, AB, T6G 2E3, Canada.
Agriculture and Agri-Food Canada, Summerland Research and Development Centre, Summerland, BC, V0H 1Z0, Canada.
J Plant Physiol. 2018 Aug;227:20-30. doi: 10.1016/j.jplph.2018.05.003. Epub 2018 May 12.
Oxygen deprivation commonly affects plants exposed to flooding and soil compaction. The resulting root hypoxia has an immediate effect on plant water relations and upsets water balance. Hypoxia inhibits root water transport and triggers stomatal closure. The processes contributing to the inhibition of root hydraulic conductivity and conductance (hydraulic conductivity of the whole root system) are complex and involve changes in root morphology and the functions of aquaporins. Aquaporins (AQPs) comprise a group of membrane intrinsic proteins that are responsible for the transport of water, as well as some small neutral solutes and ions. They respond to a wide range of environmental stresses including O deprivation, but the underlying functional mechanisms are still elusive. The aquaporin-mediated water transport is affected by the acidification of the cytoplasm and depletion of ATP that is required for aquaporin phosphorylation and membrane functions. Cytoplasmic pH, phosphorylation, and intracellular Ca concentration directly control AQP gating, all of which are related to O deprivation. This review addresses the structural determinants that are essential for pore conformational changes in AQPs, to highlight the underlying mechanisms triggered by O deprivation stress. Gene expression of AQPs is modified in hypoxic plants, which may constitute an important, yet little explored, mechanism of hypoxia tolerance. In addition to water transport, AQPs may contribute to hypoxia tolerance by transporting O, HO, and lactic acid. Responses of plants to O deprivation, and especially those that contribute to maintenance of water transport, are highly complex and entail the signals originating in roots and shoots that lead to and follow the stomatal closure. These complex responses may involve ethylene, abscisic acid, and possibly other hormonal factors and signaling molecules in ways that remain to be elucidated.
缺氧通常会影响暴露于洪水和土壤压实的植物。由此产生的根缺氧会立即影响植物的水分关系，并破坏水分平衡。缺氧抑制根的水分运输并引发气孔关闭。导致根水力传导率和传导率（整个根系的水力传导率）抑制的过程较为复杂，涉及根形态和水通道蛋白功能的变化。水通道蛋白（AQP）是一组膜内在蛋白，负责水以及一些小的中性溶质和离子的运输。它们对包括缺氧在内的广泛环境压力作出响应，但潜在的功能机制仍难以捉摸。水通道蛋白介导的水运输受到细胞质酸化和 ATP 耗竭的影响，ATP 是水通道蛋白磷酸化和膜功能所必需的。细胞质 pH、磷酸化和细胞内 Ca 浓度直接控制 AQP 的门控，所有这些都与缺氧有关。本综述探讨了 AQP 中孔构象变化所必需的结构决定因素，以强调缺氧胁迫引发的潜在机制。缺氧植物中 AQP 的基因表达发生改变，这可能是一种重要但研究甚少的缺氧耐受性机制。除了水运输外，AQP 还可能通过运输 O、HO 和乳酸来有助于缺氧耐受性。植物对缺氧的响应，特别是那些有助于维持水分运输的响应，非常复杂，涉及起源于根和茎的信号，导致和跟随气孔关闭。这些复杂的响应可能涉及乙烯、脱落酸，以及可能以尚未阐明的方式涉及其他激素因子和信号分子。
