Anderson B. E., Ward J. M., Schroeder J. I.
Department of Biology and Center for Molecular Genetics, University of California, San Diego, La Jolla, California 92093-0116.
Plant Physiol. 1994 Apr;104(4):1177-1183. doi: 10.1104/pp.104.4.1177.
The phytohormone abscisic acid (ABA) triggers stomatal closing as a physiological response to drought stress. Several basic questions limit an understanding of the mechanism of ABA reception in guard cells. Whether primary ABA receptors are located on the extracellular side of the plasma membrane, within the intracellular space of guard cells, or both remains unknown. Furthermore, it is not clear whether ABA must be transported into guard cells to exert control over stomatal movements. In the present study, a combination of microinjection into guard cells and physiological assays of stomatal movements have been performed to determine primary sites of ABA reception in guard cells. Microinjection of ABA into guard cells of Commelina communis L. resulted in injected cytosolic concentrations of 50 to 200 [mu]M ABA and in additional experiments in lower concentrations of approximately 1 [mu]M ABA. Stomata with ABA-loaded guard cells (n > 180) showed opening similar to stomata with uninjected guard cells. The viability of guard cells following ABA injection was demonstrated by neutral red staining as well as monitoring of stomatal opening. Extracellular application of 10 [mu]M ABA inhibited stomatal opening by 98% at pH 6.15 and by 57% at pH 8.0. The pH dependence of extracellular ABA action may suggest a contribution of an intracellular ABA receptor to stomatal regulation. The findings presented here show that intracellular ABA alone does not suffice to inhibit stomatal opening under the imposed conditions. Furthermore, these data provide evidence that a reception site for ABA-mediated inhibition of stomatal opening is on the extracellular side of the plasma membrane of guard cells.
植物激素脱落酸（ABA）引发气孔关闭，作为对干旱胁迫的一种生理反应。几个基本问题限制了我们对保卫细胞中ABA受体机制的理解。初级ABA受体是位于质膜的细胞外侧、保卫细胞的细胞内空间，还是两者都有，仍然未知。此外，尚不清楚ABA是否必须转运到保卫细胞中才能对气孔运动发挥控制作用。在本研究中，已进行了向保卫细胞显微注射和气孔运动生理测定相结合的实验，以确定保卫细胞中ABA受体的主要位点。向鸭跖草保卫细胞显微注射ABA，导致注射后胞质内ABA浓度达到50至200 μM，在其他实验中ABA浓度约为1 μM。装载了ABA的保卫细胞的气孔（n > 180）显示出与未注射保卫细胞的气孔相似的张开情况。通过中性红染色以及监测气孔张开，证明了注射ABA后保卫细胞的活力。在pH 6.15时，细胞外施加10 μM ABA可使气孔张开抑制98%，在pH 8.0时抑制57%。细胞外ABA作用的pH依赖性可能表明细胞内ABA受体对气孔调节有作用。此处呈现的研究结果表明，在所施加的条件下，仅细胞内ABA不足以抑制气孔张开。此外，这些数据提供了证据，表明ABA介导的气孔张开抑制的受体位点位于保卫细胞质膜的细胞外侧。
