潮间带代表性褐藻- - 鼠尾藻光抑制发生及其防御机制的研究

Living in the intertidal zone, macroalgae are exposed to drastically changing environments resulting from immersion and emersion alternation. Most of the species are sessile, thus they experience a complicated pattern of irradiance controlled by the diurnal changes and the superimposed tidal rhythm. In response to widely fluctuating environment, macroalgae have evolved many adaptive mechanisms, of which light-induced photoinhibition has been proven to be the most important one. In brown macroalgae, because of the lack of rapid allosteric changes in the light harvesting complexes, enhanced heat dissipation by de-epoxidized xanthophylls represents the major photoprotective response, thereby preventing inactivation and damage to their photosynthetic apparatus. Therefore, the photoinhibition of intertidal brown macroalgae deserves special attention for the purpose of full understanding of plant defense mechanism of light damage. Sargassum thunbergii is a representative intertidal brown macrolaga along the northwestern Pacific coast. Based on our recent study, the ?pH dependent quenching (qE) is probably not present in this species, and the zeaxanthin dependent (qZ) and photoinhibition quenching (qI) are the major components of non-photochemical quenching (NPQ), suggesting that there exists a unique photoprotective mechanism against photodamage. The research focuses on three contents as follows: 1) occurrence of photoinhibition, including spatio-temporal patterns and type of photoinhibition; 2) characteristics of photoinhibition; 3) photoprotective mechanisms against photodamage, including the components and photosynthetic plasticity of heat dissipation, xanthophyll cycle, and the role of D1-protein turnover in photoinhibition. Three experimental techniques including chlorophyll fluorescence measurements (PAM), high performance liquid chromatograph (HPLC) and photosynthetic oxygen evolution (Firesting-O2), will be used to systematically explore the process and mechanisms of photoinhibition in S. thunbergii from three viewpoints of ecology, phytophysiology and biochemistry. In addition to the advanced techniques, the collected data are analyzed by biostatistics methods, such as factorial experimental design, analysis of variance (ANOVA), principal component (PCA) and regression; the mathematical models are extensively used to fit the kinetics of photosynthetic efficiency, NPQ and de-epoxidation reaction. In conclusion, the critical scientific issues which will be resolved in this research are to determine the diversity of photoinhibition, the kinetics of chlorophyll fluorescence and photosynthetic oxygen evolution, and xanthophyll cycle, in order to elucidate the photoacclimation significance of S. thunbergii in response to varying intertidal environment.

潮间带为淹没和露空两种环境动态交替的地带，太阳日变化和潮汐循环的叠加致光照尤为复杂。认识这种特殊生境中海藻的光抑制，对于整体上理解植物光破坏防御机制具有重要价值。鼠尾藻广泛分布于潮间带，是天线系统缺乏构象快速变化的褐藻的代表性种类，我们前期研究发现, 鼠尾藻非光化学淬灭NPQ缺乏qE组分，慢速组分（qZ和qI）占据了主导地位，暗示了其光抑制防御的独特性。本项目拟从生态学、植物生理学、生物化学三个层面，开展鼠尾藻光抑制发生、特性以及防御机制的研究，以解决光抑制多样性，荧光和光合放氧动力学以及叶黄素循环三个关键科学问题, 最终阐明鼠尾藻的光适应意义。本项目实验平台采用叶绿素荧光、高效液相色谱和光合放氧Firesting-O2遥测技术；数据分析平台采用析因试验设计、方差分析、主成分分析、回归分析等生物统计学方法；另外，在光合效率、NPQ和（脱）环氧化反应动力学关键问题上重视了数学模型的运用。

潮间带为淹没和露空两种环境动态交替的地带，太阳日变化和潮汐循环的叠加致光照尤为复杂。鼠尾藻广泛分布于潮间带，是天线系统缺乏构象快速变化的褐藻的代表性种类，光抑制具有独特性。本项目从生态学、植物生理学、生物化学三个层面，采用叶绿素荧光、高效液相色谱、Firesting-O2光合放氧等技术开展了光抑制发生、特性以及防御机制的研究，具体包括：光抑制发生的时空动态; 光抑制特性及热耗散组分; (脱)环氧化反应动力学及叶黄素循环的作用；电子传递链活性。研究取得的重要结果有:1）鼠尾藻具阳生植物的光合特征，光合活性呈明显的季节变化：秋季活跃、冬季下调以及春季恢复。2）光适应与生长具权衡关系，即以减小生长为代价提高对高光生长环境的耐受力。3）高效的依赖叶黄素循环的热耗散赋予其强大的动态光抑制能力，有助于应对潮间带复杂光环境。4）NPQ中缺乏快速诱导qE组分，慢速组分(qZ和qI)在热耗散中占据主导地位，在马尾藻科中首次发现。色素滞留可确保对胁迫因子的“记忆”，从而短时间内驱动更高效的叶黄素循环与热耗散。5）鼠尾藻V-cycle 与抗氧化系统具相互协调的关系：通常情况下，V-cycle 的脱环氧化先于抗氧化系统发挥保护作用。V-cycle 对光照更敏感，而抗氧化系统对脱水更敏感，在响应不同类型胁迫时两者的角色随之变化。6）相比高等植物，光合电子传递的调节能力不足，表现在PSII与PSI的协作不明显；PSI活性以及环式电子传递的调节补偿作用有限，光系统应对环境变化主要依靠PSII的可逆失活。其中，本研究揭示的鼠尾藻光适应与生长的权衡关系、高效的依赖叶黄素循环的热耗散以及NPQ组分的特异性暗示了其光保护机制的独特性，对于整体上理解植物光破坏防御机制具有重要价值。另外，本研究揭示的在环境胁迫下以减少生长为代价优先维持生存的策略，在海藻中未见报道，但为植物的最佳防御(Optimum Defense，OD)假说提供了证据。