叶绿素荧光非光化学猝灭（NPQ）是光合生物中最重要的光保护机制之一。高等植物的NPQ依赖于PSBS蛋白，该蛋白通过感受质子梯度引起捕光复合物系统II构象变化从而激活NPQ。与高等植物不同，单细胞绿藻的NPQ依赖于LHCSR蛋白，与PSBS蛋白不同，LHCSR蛋白不仅能感受质子梯度，而且能结合色素进行直接的能量猝灭。石莼属绿藻是一种潮间带海洋大型藻类和绿潮藻类，生存的光照条件介于单细胞绿藻与陆生植物之间。本课题组首次在我国最主要的绿潮藻种浒苔中发现存在共同表达的LHCSR和PSBS的基因及蛋白，本申请书将在此研究基础上，以LHCSR和PSBS蛋白能否感受质膜质子梯度、能否结合色素、能否直接进行能量猝灭为主要研究内容，旨在揭示这两种蛋白在浒苔非光化学猝灭中的功能，同时与单细胞绿藻和高等植物的NPQ机制进行比较，为完善光合生物的光保护分子机制及其进化历程奠定基础。

Photosynthetic organisms respond to strong illumination by activating several photoprotection mechanisms. The fastest and most important among these mechanisms is non-photochemical quenching (NPQ), which dissipates the excess absorbed thermal energy and is activated within seconds after any change in light intensity. In vascular plants NPQ is essentially controlled by low pH in the thylakoid lumen, and further depends on the action of PSBS protein and xanthophylls cycle. PSBS protein acts in chloroplast lumenal pH sensing and in activation of NPQ via conformational changes in the antenna of PSII. However, in unicellular green algae, NPQ is more dependent on lumen pH and a different LHC protein, namely LHCSR. In the green algae Chlamydomonas reinhardtii LHCSR protein combines the functions of pH sensor and the chlorophyll excited state quenching needed for NPQ, which in plants is performed by two distinct protein components: PsbS and Lhcb subunits. Ulva species are intertidal pluricellular green algae in the early evolutionary stage of land colonization, has to adapt to the wide variation in light intensity, making the species particularly rewarding for studying the evolution of photoprotective mechanisms. We have found the accumulation of PSBS and LHCSR transcripts for the first time in the green tide-forming alga Ulva prolifera, but their biochemical properties are still unknown. And in this study, we will analysis biochemical functions of PSBS and LHCSR proteins in U. prolifera and confirm whether these two proteins could sense proton gradient in the thylakoid lumen, form complexes with pigments and active chlorophyll quenching and energy dissipation directly. Also, we will compare the biochemical functions of PSBS and LHCSR proteins in U. prolifera with those in unicellular and land plants, which will contribute to the evolution analysis of photoprotective mechanisms.