Phosphatase Regulation of Plant K+ Channels

9316319阿斯曼向植物施钙可防止气孔张开。钙离子的作用之一是使介导K+吸收的内向K+通道失活。最近有证据表明，这种激活是由于钙离子激活一种类似于动物蛋白磷酸酶2B的磷酸酶所致。拟议的全细胞膜片钳实验将测试蛋白磷酸酶2B是否在信号转导途径中作用于脱落酸和/或激活的G蛋白和/或肌三磷酸的下游。利用保卫细胞原生质体和保卫细胞蛋白提取物进行的平行生化研究将确定脱落酸、钙++和蛋白磷酸酶2B是否会导致相同蛋白质的去磷酸化，如果蛋白磷酸酶2B是脱落酸反应的第二介体，将被预测。对完整保卫细胞的显微注射实验将解决这样一种可能性，即蛋白磷酸酶2B作为替代或补充，是阻止气孔开放的其他环境信号的第二信使。气孔保卫细胞是调节光合作用CO2吸收和蒸腾失水的重要控制点。气孔的外皮受保卫细胞渗透膨胀和收缩的调节，保卫细胞质膜上的离子通量驱动着气孔的膨胀和收缩。一些报告表明，Ca++是脱落酸的第二信使之一，脱落酸是一种植物激素，可以阻止气孔开放，也可以减少内向K+电流。在这项建议中，补充电生理学、细胞生物学和生化实验，以检验这一假说，即调节气孔开放的环境信号通过磷酸酶2B同源物作用于内向K+通道。这些研究的结果将为深入了解植物利用第二信使系统将环境信号转化为离子通道活动的变化提供依据。研究结果也将引起环境生理学家的兴趣，他们希望了解外部和内部环境如何影响气孔开度，从而影响植物生产力。***

9316319 Assmann Application of Ca++ to plants prevents stomatal opening. One effect of Ca++ is to inactivate the inward K+ channels that mediate K+ uptake. Evidence has recently been obtained that this activation results from Ca++ activation of a phosphatase analogous to animal protein phosphatase 2B. The proposed whole-cell patch clamp experiments will test whether the protein phosphatase 2B acts " downstream" of abscisic acid and/or activated G-protein and/or inositoltriphosphate in a signal transduction pathway. Parallel biochemical studies utilizing guard cell protoplasts and guard cell protein extracts will determine whether abscisic acid, Ca++ and protein phosphatase 2B cause dephosphorylation of the same protein, as would be predicted if protein phosphatase 2B is a second mesenger for the abscisic acid response. Microinjection experiments on intact guard cells will address the possibility that protein phosphatase 2B is, alternatively or in addition, a second messenger for other environmental signals that prevent stomatal opening. %%% Stomatal guard cells are vital control points in the regulation of photosynthetic CO2 uptake and transpirational water loss. Stomatal appertures are regulated by osmotic swelling and shrinking of guard cells, driven by ion fluxes across the guard-cell plasma membrane. Several reports implicate Ca++ as one of the second messengers for abscisic acid, a plant hormone that prevents stomatal opening and also reduces inward K+ current. In this proposal complementary electrophysiological, cell biological and biochemical experiments are outlined to test the hypothesis that environmental signals which regulate stomatal opening act on inward K+ channels via a phosphatase 2B homologue. Results from these studies will provide insight into the second messenger systems utilized by plants to translate environmental signals into alterations of ion channel activity. Results will also be of interest to environmental physiologis ts who would like to understand how the external and internal environments affects stomatal apertures and thereby impacts plant productivity. ***