Sensory Transduction of the Green Light-Induced Reversal of the Stomatal Response to Blue Light: Mechanisms and Functional Implications

保卫细胞调节气孔，控制叶片气体交换，调节光合作用和植物水分利用。保卫细胞通过复杂的感觉转导级联反应感知许多环境和荷尔蒙信号。光是调节气孔反应的主要信号。像许多其他植物细胞一样，保卫细胞有一种特殊的感官传导级联，它使用蓝光作为环境信号。最近，NSF支持的保卫细胞研究发现，蓝光刺激的气孔开放可以完全被绿光逆转。在光脉冲研究中可以观察到绿色反转：如果在蓝光脉冲之后是绿光脉冲，则不能观察到气孔打开，如果在绿脉冲之后是第二个蓝光脉冲，则恢复气孔打开响应。在连续的蓝绿光照射下，也观察到了绿色反转。在这种情况下，反转取决于绿光剂量，在绿光与蓝光比例为2：1的情况下观察到完全反转。蓝光刺激开放的作用光谱具有植物中许多蓝光反应的典型的“三指”精细结构。绿光反转的作用光谱也显示出红移约90 nm的三指结构。类胡萝卜素玉米黄质的吸收光谱与蓝光刺激开放的作用光谱非常匹配，而蛋白质环境中的类胡萝卜素异构化往往使吸收光谱红移。这个项目的目标之一是确定介导蓝绿逆转的光化学反应的性质，所涉及的发色团的身份(S)，以及导致蓝光刺激的开放的绿色逆转的早期感觉转导事件。用高效液相色谱、紫外可见光谱、共振拉曼光谱和傅里叶变换红外吸收光谱(FTIR)对早期感官传导步骤的光化学进行研究。为了确定它们的遗传损伤是否损害了蓝绿色逆转反应，将研究几个光感受器突变体，如npq1和Pho1 Pho2。另一个目的是研究保卫细胞中的蓝绿色逆转反应是否感知到达生长在日照和阴暗条件下的叶片的太阳辐射的蓝绿光子比，并将其转化为适应策略。这些研究的成功将表征一种新的植物细胞光生物学机制，它可以调节植物的驯化和适应。最近发现的绿光逆转了蓝光刺激的气孔开放，为植物细胞对光的反应方式提供了新的理解。详细研究介导蓝/绿反转的光化学反应可能为明确识别保卫细胞中的蓝光感受器开辟道路。此外，对完整叶片蓝/绿反转的研究可以极大地丰富我们对叶片适应日照和遮荫条件的理解。该奖项支持的研究项目的成功将极大地丰富我们对植物功能的知识。

Regulation of stomatal apertures by guard cells controls leaf gas exchange and modulates photosynthesis and plant water use. Guard cells sense many environmental and hormonal signals through complex sensory transducing cascades. Light is a major signal modulating stomatal responses. Like many other plant cells, guard cells have a specific sensory transducing cascade that uses blue light as an environmental signal. Recent, NSF-supported studies with guard cells have discovered that blue light-stimulated stomatal opening can be fully reversed by green light. The green reversal can be observed in light-pulse studies: If a pulse of blue light is followed by a green light pulse, stomatal opening is not observed, if the green pulse is followed by second blue light pulse, the opening response is restored. The green reversal is also observed under continuous blue and green illumination. In this case the reversal depends on the green light dose, with full reversal observed under a 2:1 green to blue light ratio. The action spectrum for blue light-stimulated opening has the "3-finger" fine structure typical of many blue light responses in plants. The action spectrum for the green reversal also shows a 3-finger structure, red-shifted by about 90 nm. The carotenoid, zeaxanthin has an absorption spectrum closely matching the action spectrum for blue light-stimulated opening, and carotenoid isomerization in a protein environment often red-shifts the absorption spectrum. One of the objectives of this project is to determine the nature of the photochemical reactions mediating the blue-green reversal, the identity of the involved chromophore(s), and the early sensory transducing events leading to the green reversal of blue light-stimulated opening. The photochemistry of the early sensory transducing steps will be studied by HPLC, UV-visible, resonance Raman, and Fourier Transform Infrared Absorption Spectroscopy (FTIR). Several photoreceptor mutants such as npq1 and phot1 phot2 will be studied in order to determine whether their genetic lesions have impaired the blue green reversal response. Another objective is to investigate whether the blue green reversal response in guard cells senses the blue:green photon ratio of solar radiation reaching leaves growing in sun and shade conditions, and transduces it into acclimation strategies. Success in these studies will characterize a new photobiological mechanism of plant cells, which could mediate plant acclimations and adaptations. The recently discovered reversal of blue light-stimulated stomatal opening by green light offers a new understanding of the ways plant cells respond to light. Detailed investigation of the photochemical reactions mediating the blue/green reversal could open the way for the unambiguous identification of a blue light photoreceptor in guard cells. In addition, research on the blue/green reversal in the intact leaf could significantly enrich our understanding of ways by which leaves acclimate to sun and shade conditions. Success in the research project supported by this award should significantly enrich our knowledge of plant function.