Purdue University School of Science at Indianapolis, Department of Biology, Indianapolis, Indiana 46223.
Plant Physiol. 1990 Mar;92(3):822-30. doi: 10.1104/pp.92.3.822.
The alga Mougeotia has a large central chloroplast whose positioning is regulated by photoactivation of phytochrome, possibly via modulation of cytosolic calcium (Serlin B, Roux SJ [1984] Proc Natl Acad Sci USA 81: 6368-6372). We used the patch clamp technique to examine the effects of red and far-red light on ion channel activity in the plasma membrane of Mougeotia protoplasts to determine if ion channels play a role in chloroplast movement. Patch clamping in the cell-attached mode reveals two channels of about 2 and 4 picoamperes amplitude at 0 millivolt (inside pipette) and estimated conductances of 30 and 65 picosiemens. They are activated by red light irradiation after a lag period of about 2 to 5 minutes. Far-red light, when applied immediately after red light irradiation, reverses this activation; otherwise it has no effect. This result implicates phytochrome. The addition of the calcium ionophore, A23187, also activates ion channel activity after a lag of a few minutes. The channels are not specific for calcium since they are present when calcium is removed from the external and pipette media. They are inhibited by quaternary ammonium ions. Thus, we believe they are calcium-activated potassium channels. Their possible role in chloroplast positioning is discussed.
绿藻（Mougeotia）具有一个大型中央叶绿体，其位置由光敏色素的光激活调节，可能通过细胞溶质钙的调制来实现（Serlin B，Roux SJ [1984] Proc Natl Acad Sci USA 81: 6368-6372）。我们使用膜片钳技术研究红光和远红光对绿藻原生质体质膜离子通道活性的影响，以确定离子通道是否在叶绿体运动中起作用。细胞贴附模式的膜片钳记录揭示了两个幅度约为 2 和 4 皮安的通道，在 0 毫伏（管内），估计电导分别为 30 和 65 皮西门子。它们在红光照射后经过约 2 到 5 分钟的延迟期被激活。远红光在红光照射后立即施加时会逆转这种激活，否则没有效果。这一结果暗示了光敏色素的参与。钙离子载体 A23187 的添加也会在几分钟的延迟后激活离子通道活性。这些通道不是特异性的钙通道，因为当从外部和管内介质中去除钙时，它们仍然存在。它们被季铵离子抑制。因此，我们认为它们是钙激活的钾通道。讨论了它们在叶绿体定位中的可能作用。
