Cytosolic abscisic acid activates guard cell anion channels without preceding Ca2+ signals
Cytosolic abscisic acid activates guard cell anion channels without preceding Ca2+ signals
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DOI：
10.1073/pnas.0500146102
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发表时间：
2005-03-15
影响因子：
11.1
通讯作者：
Hedrich, R
中科院分区：
文献类型：
--
作者：
Levchenko, V;Konrad, KR;Hedrich, R
植物激素脱落酸（阿坝）报告植物的水分状况并诱导气孔关闭。保卫细胞阴离子通道在这种反应中起着核心作用，因为它们介导阴离子流出，进而引起去极化诱导的K+释放。我们记录了阿坝信号的早期步骤，在完整植物的保卫细胞中引入多管微电极。外部阿坝处理后，阴离子通道瞬时激活后，约2分钟的滞后期。预期的胞质阿坝受体，离子导入阿坝加载到细胞质中开始上升的阴离子电流没有延迟。这些阿坝反应可以在静息时和在很大程度上去极化电位（例如，0 mV），排除了通过超极化激活的钙通道的信号转导。同样，阿坝刺激没有引起细胞质游离钙浓度的上升。然而，阴离子通道功能需要约100 nM背景Ca 2+的存在，因为在加载Ca 2+螯合剂1，2-双（2-氨基苯氧基）乙烷-N，N，N '，N'-四乙酸酯后，阿坝对阴离子通道的作用被抑制。事件链似乎非常直接，因为没有测试的假定ABA信号中间体（肌醇1，4，5三磷酸，肌醇六磷酸，烟酸腺嘌呤二核苷酸磷酸，和环ADP-核糖），可以模拟阿坝作为阴离子通道激活剂。在膜片钳实验中，胞浆阿坝也诱发由R-和S-型阴离子通道进行的阴离子电流瞬变。该反应具有剂量依赖性，在2.6 μ M阿坝时达到半最大激活。我们的研究指出，阿坝途径启动阿坝结合到细胞溶质受体，在几秒钟内激活阴离子通道，并反过来导致质膜的去极化。
The phytohormone abscisic acid (ABA) reports on the water status of the plant and induces stomatal closure. Guard cell anion channels play a central role in this response, because they mediate anion efflux, and in turn, cause a depolarization-induced K+ release. We recorded early steps in ABA signaling, introducing multibarreled microelectrodes in guard cells of intact plants. Upon external ABA treatment, anion channels transiently activated after a lag phase of approximate to 2 min. As expected for a cytosolic ABA receptor, iontophoretic ABA loading into the cytoplasm initiated a rise in anion current without delay. These ABA responses could be elicited repetitively at resting and at largely depolarized potentials (e.g., 0 mV), ruling out signal transduction by means of hyperpolarization-activated calcium channels. Likewise, ABA stimulation did not induce a rise in the cytosolic free-calcium concentration. However, the presence of approximate to 100 nM background Ca2+ was required for anion channel function, because the action of ABA on anion channels was repressed after loading of the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate. The chain of events appears very direct, because none of the tested putative ABA-signaling intermediates (inositol 1,4,5 trisphosphate, inositol hexakisphosphate, nicotinic acid adenine dinucleotide phosphate, and cyclic ADP-ribose), could mimic ABA as anion channel activator. In patch-clamp experiments, cytosolic ABA also evoked anion current transients carried by R- and S-type anion channels. The response was dose-dependent with half-maximum activation at 2.6 mu M ABA. Our studies point to an ABA pathway initiated by ABA binding to a cytosolic receptor that within seconds activates anion channels, and in turn, leads to depolarization of the plasma membrane.