SGER: Sensory Transduction of Blue Light in Corn coleoptiles

本提案要求小额探索性研究拨款，为类胡萝卜素在玉米胚囊的致光性反应中作为蓝光感受器起作用的假设的关键测试提供初步数据。目前学界认为蓝光感受器的作用与黄素或黄素蛋白有关。然而，该实验室最近的工作为类胡萝卜素玉米黄质在蓝光光接受中的作用提供了诱人的证据。这里提出的研究解决了这个分子是否作为胶体向光性的光感受器的问题，胶体向光性是一种具有良好特征的蓝光反应。对玉米胚芽的初步研究表明，它们控制着叶黄素循环，并且玉米质浓度与它们的光环境有关。拟议的实验旨在将变色反应的程度与胚芽虫中普遍存在的玉米黄质浓度相关联，并确定胚芽虫叶绿体是否表现出蓝光反应。其他对色素组成发生改变的玉米突变体进行的实验将寻求将感光性的变化与其色素含量联系起来。对胚芽鞘系统中蓝光感知机制的研究将大大提高我们对植物蓝光感知转导的认识。植物对环境最基本的反应之一是，幼芽的生长尖端转向向光方向生长。蓝光在引起这种反应方面是最有效的，但植物尖端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合物吸收，但化学光感受器尚未被确定。确定蓝光光感受器的性质将对理解这一基本植物反应作出重要贡献。间接证据使该领域的大多数研究人员相信，光感受器可能是一种被称为“黄素”的有机分子。然而，Zeiger博士已经获得了一些结果，表明另一类有机分子，一种“类胡萝卜素”可能是真正的蓝光受体。如果类胡萝卜素确实是蓝光感受器，这将是一个非常重要的进展，但目前的证据还不完整，不足以证明对这一主题开展全面的研究计划是合理的。这项探索性研究小额赠款将允许Zeiger博士开发足够的初步数据，以确定是否应该开展一个全面的项目来研究类胡萝卜素作为蓝光光感受器的功能。

This proposal requests a Small Grant for Exploratory Research to develop preliminary data for a critical test of the hypothesis that carotenoids function as blue light photoreceptors in the phototropic response of corn coleoptiles. Current thinking in the field ascribes the role of blue light photoreceptor to flavins or flavoproteins. Recent work in this laboratory, however, has provided tantalizing evidence for a role of the carotenoid, zeaxanthin in blue light photoreception. The research proposed here addresses the question of whether this molecule serves as the photoreceptor for coleoptile phototropism, a well characterized blue light response. Pilot studies with corn coleoptiles have shown that they operate the xanthophyll cycle and have zeanthin concentrations that track their light environment. Proposed experiments are designed to correlate the extent of the phototropic response with prevailing zeaxanthin concentrations in the coleoptile, and to establish whether coleoptile chloroplasts show a blue light response. Other experiments with corn mutants having an altered pigment composition will seek to correlate changes in phototropic sensitivity with their pigment content. Characterization of the blue light sensing mechanism in the coleoptile system would significantly enhance our understanding of blue light sensory transduction in plants. %%% One of the most fundamental responses of a plant to its environment is that the growing tip of a young plant shoot turns and grows toward light. Blue light is most effective in eliciting this response, but the mechanism by which plant tips sense blue light is not yet understood. As the first step in the response blue light must be absorbed by a specific chemical compound, but the chemical photoreceptor has not yet been identified with certainty. Establishing the nature of the blue light photoreceptor would be an important contribution to understanding of this fundamental plant response. Circumstantial evidence has led most investigators in the field to believe that the photoreceptor is probably a type of organic molecule known as a "flavin". Dr. Zeiger, however, has obtained some results suggesting that a different class of organic molecule, a "carotenoid" may be the real blue light receptor. If a carotenoid is, indeed, the blue light photoreceptor this would be a very important advance, but the evidence at present is too incomplete to justify launching a full scale research program on the subject. This Small Grant for Exploratory Research will permit Dr. Zeiger to develop sufficient preliminary data to determine whether a full scale project should be undertaken to study the function of carotenoids as blue light photoreceptors.