Acclimation of Photosynthetic Organisms to High Light: Molecular and Genetic Dissection

超过植物用于光化学的光子通量密度会激活有助于保护光合装置免受光损伤的过程；具体地说，植物可以将大部分多余的激发能以热的形式散发出去。这种被测量为叶绿素荧光的非光化学猝灭（NPQ）的非辐射能量耗散可能是几个过程的结果。其中一个过程是通过叶黄素循环产生玉米黄素（它可以直接淬灭被激发的叶绿素分子），发生在光收集天线复合物中。其他能量耗散过程，如P680+和QA-之间的电荷重组和光系统II （PSII）周围的循环电子流，与反应中心有关。这项资助的目的是阐明这些过程的机制及其对光保护的相对重要性，使用衣藻作为模式生物。突变体是通过插入诱变产生的，这将允许相对容易地分离感兴趣的基因。在强光或弱光下生长的突变株的生理特征揭示了几种新的突变体，包括那些在1)叶黄素循环，2)其他能量耗散机制，3)NPQ调节和4)清除氧自由基方面存在缺陷的突变体。建议继续对已分离的突变株进行生理、生化和遗传分析。这些研究将帮助我们评估已知光保护过程的重要性，发现控制这些过程的特定机制，甚至可能揭示有助于光保护的新机制。

9506254 Grossman Photon flux densities that are in excess of what a plant can use for photochemistry result in the activation of processes that help protect the photosynthetic apparatus against photodamage; specifically, plants can dissipate much of the excess excitation energy as heat. This nonradiative energy dissipation, which is measured as nonphotochemical quenching (NPQ) of chlorophyll fluorescence, is probably the result of several processes. One of these processes, the generation of zeaxanthin (which may directly quench excited chlorophyll molecules) via the xanthophyll cycle, occurs in the light- harvesting antenna complexes. Other energy dissipating processes, such as charge recombination between P680+ and QA- and a cyclic electron flow around photosystem II (PSII), are associated with the reaction centers. The objective of this grant is to elucidate the mechanisms underlying these processes and their relative importance for photoprotection, using Chlamydomonas as a model organism. Mutants have been generated by insertional mutagensis, which will allow for the relatively facile isolation of the genes of interest. Physiological characterizations of the mutant strains grown in high or low light have revealed several novel classes of mutants, including those that appear to be defective in 1) the xanthophyll cycle, 2) other mechanisms of energy dissipation, 3) the regulation of NPQ, and 4) scavenging of oxygen radicals. It is proposed to continue physiological, biochemical and genetic analyses of the mutant strains that have already been isolated. These studies will help us evaluate the importance of known photoprotective processes, discover specific mechanisms that govern these processes and perhaps even unveil novel mechanisms that contribute to photoprotection.