Felle H H, Hanstein S, Steinmeyer R, Hedrich R
Botanisches Institut I, Universität Giessen, Senckenbergstrasse 17, D-35390 Giessen, Germany.
Plant J. 2000 Nov;24(3):297-304. doi: 10.1046/j.1365-313x.2000.00878.x.
Stomatal movement is accomplished by changes in the ionic content within guard cells as well as in the cell wall of the surrounding stomatal pore. In this study, the sub-stomatal apoplastic activities of K+, Cl-, Ca2+ and H+ were continuously monitored by inserting ion-selective micro-electrodes through the open stomata of intact Vicia faba leaves. In light-adapted leaves, the mean activities were 2.59 mM (K+), 1.26 mM (Cl-), 64 microM (Ca2+) and 89 microM (H+). Stomatal closure was investigated through exposure to abscisic acid (ABA), sudden darkness or both. Feeding the leaves with ABA through the cut petiole initially resulted in peaks after 9-10 min, in which Ca2+ and H+ activities transiently decreased, and Cl- and K+ activities transiently increased. Thereafter, Ca2+, H+ and Cl- activities completely recovered, while K+ activity approached an elevated level of around 10 mM within 20 min. Similar responses were observed following sudden darkness, with the difference that Cl- and Ca2+ activities recovered more slowly. Addition of ABA to dark-adapted leaves evoked responses of Cl- and Ca2+ similar to those observed in the light. K+ activity, starting from its elevated level, responded to ABA with a transient increase peaking around 16 mM, but then returned to its dark level. During stomatal closure, membrane potential changes in mesophyll cells showed no correlation with the K+ kinetics in the sub-stomatal cavity. We thus conclude that the increase in K+ activity mainly resulted from K+ release by the guard cells, indicating apoplastic compartmentation. Based on the close correlation between Cl- and Ca2+ changes, we suggest that anion channels are activated by a rise in cytosolic free Ca2+, a process which activates depolarization-activated K+ release channels.
气孔运动是通过保卫细胞内离子含量以及周围气孔孔壁的变化来实现的。在本研究中，通过完整蚕豆叶片开放的气孔插入离子选择性微电极，连续监测了气孔下质外体中K⁺、Cl⁻、Ca²⁺和H⁺的活性。在光适应叶片中，平均活性分别为2.59 mM（K⁺）、1.26 mM（Cl⁻）、64 μM（Ca²⁺）和89 μM（H⁺）。通过施加脱落酸（ABA）、突然遮光或两者结合来研究气孔关闭情况。通过切断的叶柄向叶片施加ABA，最初在9 - 10分钟后出现峰值，其中Ca²⁺和H⁺活性短暂下降，Cl⁻和K⁺活性短暂增加。此后，Ca²⁺、H⁺和Cl⁻活性完全恢复，而K⁺活性在20分钟内接近10 mM的升高水平。突然遮光后观察到类似反应，但不同的是Cl⁻和Ca²⁺活性恢复得更慢。向暗适应叶片添加ABA引起的Cl⁻和Ca²⁺反应与在光照下观察到的相似。K⁺活性从其升高水平开始，对ABA的反应是短暂增加，峰值约为16 mM，但随后恢复到暗适应水平。在气孔关闭过程中，叶肉细胞的膜电位变化与气孔下腔中的K⁺动力学无关。因此，我们得出结论，K⁺活性的增加主要源于保卫细胞释放K⁺，表明存在质外体分隔。基于Cl⁻和Ca²⁺变化之间的密切相关性，我们认为阴离子通道由胞质游离Ca²⁺的升高激活，这一过程激活了去极化激活型K⁺释放通道。
