Sensory Transduction of Blue Light in Guard Cells

本研究的目的是探讨类胡萝卜素在保护细胞蓝光光接收中的可能作用。保护细胞对蓝光的反应包括淀粉水解、苹果酸生物合成和保护细胞膜上的质子泵送。这些过程调节保护细胞的渗透电位和气孔开度，这在数量上与蓝光入射影响率有关。最近一项关于保护细胞色素的研究表明，保护细胞类胡萝卜素的吸收光谱与蓝光刺激下气孔导度增加的作用光谱密切匹配，这表明类胡萝卜素在光接受中的作用。有人提出，类胡萝卜素在类囊体膜中可以在两种不同的状态下起作用。在类囊体的中等跨膜电位下，类胡萝卜素将作为辅助色素将吸收的光能汇集到光合反应中。在高跨膜电位下，类胡萝卜素会远离叶绿素分子，在蓝光激发下，会激活一个感觉转导过程，导致典型的蓝光反应。支持这一假设的初步结果包括保护细胞叶绿体固有蓝光响应的表征，以及玉米黄质生物合成抑制剂DTT对蓝光刺激下气孔打开的特异性抑制。此外，通过测定气孔导度和蓝光敏感性比较的原始棉系和高级棉系F2植株的气孔导度、保护细胞叶绿体对蓝光的响应强度以及保护细胞中玉米黄质浓度，结果表明，高导度植株的保护细胞对蓝光的响应大，玉米黄质浓度高，反之亦然。该研究将利用光谱学、生理学、生物化学和遗传学方法研究保护细胞和胚芽鞘，以探索类胡萝卜素（可能是玉米黄质）在植物细胞蓝光感觉转导中的作用。植物对环境最基本的反应之一是对蓝光的反应。蓝光刺激幼嫩植物的生长尖端转向向光生长，并控制叶片气孔（气孔）的开放，气孔允许气体和水在叶片表面交换。植物细胞感知蓝光的机制尚不清楚。作为反应的第一步，蓝光必须被一种特定的化学光感受器吸收，但这种光感受器尚未被确定。间接证据使该领域的许多研究人员相信，光感受器是一种被称为“黄素”的有机分子。然而，齐格博士有证据表明，另一类分子，一种“类胡萝卜素”，可能是蓝光受体。这项研究的目的是确定类胡萝卜素是否是真正的蓝光受体。确定蓝光光感受器的性质将对理解这种植物对环境的基本反应作出非常重要的贡献

9311042 Zeiger The goal of this research is to investigate possible roles of carotenoids in blue light photoreception in guard cells. Blue light responses of guard cells include starch hydrolysis, malate biosynthesis, and proton pumping at the guard cell plasma membrane. These processes modulate guard cell osmotic potentials and stomatal apertures that are quantitatively related to incident fluence rates of blue light. A study on guard cell pigments has recently shown that absorption spectra of guard cell carotenoids closely match an action spectrum of the blue light-stimulated increases in stomatal conductances, pointing to a role of carotenoids in photoreception. It is proposed that a carotenoid in the thylakoid membrane can function in two alternative states. At moderate transmembrane potentials across the thylakoid, the carotenoid would operate as an accessory pigment funneling absorbed light energy into photosynthetic reactions. At high transmembrane potentials, the carotenoid would move away from the chlorophyll molecules and, upon blue light excitation, would activate a sensory transduction process leading to typical blue light responses. Initial results supporting this hypothesis include the characterization of intrinsic blue light responses of guard cell chloroplasts, and a specific inhibition of the blue light-stimulated stomatal opening by the inhibitor of zeaxanthin biosynthesis, DTT. In addition, measurements of rates of stomatal conductances, the magnitude of blue light responses of guard cell chloroplasts, and zeaxanthin concentrations in guard cells of F2 plants from a cross between a primitive and an advanced cotton line with contrasting stomatal conductances and blue light sensitivity, showed that plants with high conductances had guard cells with large blue light responses and a high zeaxanthin concentration, and vice versa. The proposed research will use spectroscopic, physiological, biochemical and genetic approaches with guard cell s and coleoptiles, to probe the involvement of a carotenoid, possibly zeaxanthin, in blue light sensory transduction in plant cells. %%% One of the most fundamental responses of a plant to the environment is the response to blue light. Blue light stimulates the growing tip of a young plant to turn and grow toward light, and controls the opening of pores in leaves (stomata) that allow gas and water exchange across the leaf surface. The mechanism by which plant cells sense blue light is not yet understood. As the first step in the response, blue light must be absorbed by a specific chemical photoreceptor, but this photoreceptor has not yet been identified with certainty. Circumstantial evidence has led many investigators in the field to believe that the photoreceptor is a type of organic molecule known as a "flavin". Dr. Zeiger, however, has evidence suggesting that a different class of molecule, a "carotenoid" may, instead, be the blue light receptor. The goal of this research is to determine whether the carotenoid is the real blue light receptor. Establishing the nature of the blue light photoreceptor would be a very important contribution to understanding of this fundamental plant response to the environment.***