潮间带是海洋生物登陆进化为陆地生物的重要场所，大部分栖息在潮间带的大型海藻在退潮时处于严酷胁迫环境中，其中藻体利用叶黄素循环进行光保护是海藻抗逆研究的热点。叶黄素循环包括二种关键酶：脱环氧酶（VDE）和环氧酶（ZEP），其中VDE是调控叶黄素循环的关键。一般认为，VDE只在光照条件下才有活性。然而，我们的前期研究表明，潮间带大型海藻孔石莼VDE在黑暗时仍有较强活性。为此，本项目以孔石莼为对象，利用不同的专一性抑制剂，首先分别抑制光合线性电子传递、环式电子传递和叶绿体呼吸等，然后再分别抑制ZEP和VDE活性，以阐明电子传递与VDE和ZEP之间的协同关系；分离处于不同状态的孔石莼类囊体膜尤其是LHCII复合体，研究VDE和ZEP与类囊体膜的结合情况，解析叶黄素循环调控机制。同时，比较分析不同进化程度物种的叶黄素循环，阐释其演化过程。本项目的完成将可以明确孔石莼叶黄素循环机制及调控规律。

Coastal intertidal zone is a crucial place for living organisms landing from the marine to the terrestrial habitat. Most of the macro-algae inhabiting in intertidal zone frequently endure harsh abiotic stress during low tide. Xanthophyll cycle, which is used by these organisms to protect them against potential photodamages, is one of the focus among the field of studying the stress tolerance of algae. Xanthophyll cycle is composed of two key enzymes, violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZEP), and the VDE has a pivotal role in the regulation of xanthophyll cycle. It is generally accepted that the illumination is required for the catalytic activities of VDE. However, our previous work with intertidal macro-alga, Ulva pertusa, shows that the VDE remains active under darkness. Therefore, Ulva pertusa would be used in this project to investigate the coordinating relationships between electron flows along the thylakoid membrane and the activities of the enzymes VDE and ZEP by applying a variety of specific metabolic inhibitors to inhibit photosynthetic linear electron flow, cyclic electron flow around PSI and chlororespiration, respectively, and then to inhibit the activities of VDE and ZEP, respectively. The results would be comprehensively analyzed by comparison with those obtained from other photosynthetic organisms of different degrees of evolution. Meanwhile, examine the content of VDE and ZEP combined with thylakoid membrane, especially LHCII complex, of the Ulva pertusa treated with various levels of illumination. The purpose of this project is to elucidate the regulation mechanisms of xanthophyll cycle in intertidal macro-alga Ulva pertusa, and to track the evolution process of xanthophyll cycle.