Sensory Transduction of Blue Light in Guard Cells

小行星9311042 本研究的目的是探讨类胡萝卜素在保卫细胞蓝光光感受中的可能作用。 保卫细胞的蓝光反应包括淀粉水解、苹果酸生物合成和保卫细胞质膜上的质子泵。 这些过程调节保卫细胞的渗透势和气孔开度是定量相关的入射蓝光的注量率。 最近对保卫细胞色素的研究表明，保卫细胞类胡萝卜素的吸收光谱与蓝光刺激气孔导度增加的作用光谱密切匹配，指出类胡萝卜素在光感受中的作用。 有人提出，类囊体膜中的类胡萝卜素可以在两种可选的状态下发挥作用。 在中等跨膜电位下，类胡萝卜素作为辅助色素参与光合反应，吸收光能。 在高跨膜电位下，类胡萝卜素将远离叶绿素分子，并且在蓝光激发下，将激活感觉转导过程，导致典型的蓝光响应。 支持这一假设的初步结果包括固有的保卫细胞叶绿体的蓝光反应的表征，和特定的抑制剂玉米黄质生物合成，DTT的蓝光刺激的气孔开放。 此外，气孔导度的速率、保卫细胞叶绿体的蓝光响应的幅度和保卫细胞中玉米黄质浓度的测量来自原始棉花品系和具有对比气孔导度和蓝光敏感性的高级棉花品系之间的杂交的F2植物，表明具有高导度的植物具有具有大蓝光响应和高玉米黄质浓度的保卫细胞，且反之亦然。 这项研究将利用保卫细胞和胚芽鞘的光谱学、生理学、生化学和遗传学方法，探讨类胡萝卜素（可能是玉米黄质）在植物细胞蓝光感觉传导中的作用。 植物对环境最基本的反应之一是对蓝光的反应。 蓝光刺激幼苗的生长尖端转向并朝着光线生长，并控制叶片中的气孔（气孔）的打开，从而允许气体和水分在叶片表面进行交换。 植物细胞感知蓝光的机制尚不清楚。 作为反应的第一步，蓝光必须被特定的化学感光体吸收，但这种感光体尚未被确定。 间接证据使该领域的许多研究人员相信感光体是一种被称为“黄素”的有机分子。 然而，Zeiger博士有证据表明，一种不同类型的分子，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实的蓝光受体。 确定蓝光感光器的性质将对理解这一点做出非常重要的贡献 植物对环境的基本反应 *

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.***