Lew R R, Serlin B S, Schauf C L, Stockton M E
Purdue University School of Science at Indianapolis, Department of Biology, Indianapolis, Indiana 46223.
Plant Physiol. 1990 Mar;92(3):831-6. doi: 10.1104/pp.92.3.831.
Phytochrome mediates chloroplast movement in the alga Mougeotia, possibly via changes in cytosolic calcium. It is known to regulate a calcium-activated potassium channel in the algal plasma membrane. As part of a characterization of the potassium channel, we examined the properties of calcium activation. The calcium ionophore A23187 activates the channel at external [Ca(2+)] as low as 20 micromolar. However, external [Ca(2+)] is not required for activation of the channel by photoactivated phytochrome. Furthermore, when an inhibitor of calcium release from internal stores, 8-(diethylamino)-octyl-3,4,5-trimethoxybenzoate, hydrochloride (TMB-8), is present, red light no longer stimulates channel activity. We conclude that phytochrome activates the plasma membrane potassium channel by releasing calcium from intracellular calcium vesicles; the elevated cytosolic calcium then stimulates channel activity by an unknown mechanism. In the presence of TMB-8, red light does induce chloroplast rotation; thus, potassium channel activation may not be coupled to chloroplast rotation.
光敏色素可能通过胞质钙的变化介导藻类转板藻中的叶绿体运动。已知它能调节藻类质膜中的一种钙激活钾通道。作为对该钾通道特性研究的一部分，我们检测了钙激活的特性。钙离子载体A23187在外部[Ca(2+)]低至20微摩尔时就能激活该通道。然而，光活化的光敏色素激活该通道并不需要外部[Ca(2+)]。此外，当存在一种抑制内部钙库释放钙的抑制剂，即盐酸8 -（二乙氨基）-辛基-3,4,5 -三甲氧基苯甲酸酯（TMB - 8）时，红光不再刺激通道活性。我们得出结论，光敏色素通过从细胞内钙囊泡释放钙来激活质膜钾通道；升高的胞质钙随后通过一种未知机制刺激通道活性。在TMB - 8存在的情况下，红光确实会诱导叶绿体旋转；因此，钾通道激活可能与叶绿体旋转不相关。
