Staxen I, Pical C, Montgomery L T, Gray J E, Hetherington A M, McAinsh M R
Institute of Environmental and Natural Sciences, Department of Biological Sciences, Lancaster University, Lancaster LA1 4YQ, United Kingdom.
Proc Natl Acad Sci U S A. 1999 Feb 16;96(4):1779-84. doi: 10.1073/pnas.96.4.1779.
Oscillations in cytosolic free Ca2+ concentration ([Ca2+]cyt) are an important component of Ca2+-based signal transduction pathways. This fact has led us to investigate whether oscillations in [Ca2+]cyt are involved in the response of stomatal guard cells to the plant hormone abscisic acid (ABA). We show that ABA induces oscillations in guard-cell [Ca2+]cyt. The pattern of the oscillations depended on the ABA concentration and correlated with the final stomatal aperture. We examined the mechanism by which ABA generates oscillations in guard-cell [Ca2+]cyt by using 1-(6-[17beta-3-methoxyestra-1,3, 5(10)-trien-17-yl]aminohexyl)-1H-pyrrole-2,5-dione (U-73122), an inhibitor of phosphoinositide-specific phospholipase C (PI-PLC)-dependent processes in animals. U-73122 inhibited the hydrolysis of phosphatidylinositol 4,5-bisphosphate by a recombinant PI-PLC, isolated from a guard-cell-enriched cDNA library, in a dose-dependent manner. This result confirms that U-73122 is an inhibitor of plant PI-PLC activity. U-73122 inhibited both ABA-induced oscillations in [Ca2+]cyt and stomatal closure. In contrast, U-73122 did not inhibit external Ca2+-induced oscillations in guard-cell [Ca2+]cyt and stomatal closure. Furthermore, there was no effect of the inactive analogue 1-(6-[17beta-3-methoxyestra-1,3, 5(10)-trien-17-yl]aminohexyl)-2,5-pyrrolidinedione on recombinant PI-PLC activity or ABA-induced and external Ca2+-induced oscillations in [Ca2+]cyt and stomatal closure. This lack of effect suggests that the effects of U-73122 in guard cells are the result of inhibition of PI-PLC and not a consequence of nonspecific effects. Taken together, our data suggest a role for PI-PLC in the generation of ABA-induced oscillations in [Ca2+]cyt and point toward the involvement of oscillations in [Ca2+]cyt in the maintenance of stomatal aperture by ABA.
胞质游离钙离子浓度（[Ca2+]cyt）的振荡是基于钙离子的信号转导途径的重要组成部分。这一事实促使我们研究[Ca2+]cyt的振荡是否参与气孔保卫细胞对植物激素脱落酸（ABA）的响应。我们发现ABA可诱导保卫细胞[Ca2+]cyt产生振荡。振荡模式取决于ABA浓度，并与最终气孔孔径相关。我们通过使用1-(6-[17β-3-甲氧基雌甾-1,3,5(10)-三烯-17-基]氨基己基)-1H-吡咯-2,5-二酮（U-73122）来研究ABA在保卫细胞[Ca2+]cyt中产生振荡的机制，U-73122是一种动物中依赖磷脂酰肌醇特异性磷脂酶C（PI-PLC）的过程的抑制剂。U-73122以剂量依赖的方式抑制从富含保卫细胞的cDNA文库中分离出的重组PI-PLC对磷脂酰肌醇4,5-二磷酸的水解。这一结果证实U-73122是植物PI-PLC活性的抑制剂。U-73122既抑制ABA诱导的[Ca2+]cyt振荡，也抑制气孔关闭。相反，U-73122不抑制外部钙离子诱导的保卫细胞[Ca2+]cyt振荡和气孔关闭。此外，无活性类似物1-(6-[17β-3-甲氧基雌甾-1,3,5(10)-三烯-17-基]氨基己基)-2,5-吡咯烷二酮对重组PI-PLC活性或ABA诱导的以及外部钙离子诱导的[Ca2+]cyt振荡和气孔关闭均无影响。这种无影响表明U-73122在保卫细胞中的作用是抑制PI-PLC的结果，而非非特异性效应的结果。综上所述，我们的数据表明PI-PLC在ABA诱导的[Ca2+]cyt振荡的产生中起作用，并表明[Ca2+]cyt振荡参与ABA对气孔孔径的维持。
