Ocean School, Yantai University, Yantai, 264005, People's Republic of China.
Photosynth Res. 2021 Jun;148(3):87-99. doi: 10.1007/s11120-021-00836-0. Epub 2021 May 2.
Non-photochemical quenching (NPQ) of photosystem II (PSII) fluorescence is one of the most important protective mechanisms enabling the survival of phototropic organisms under high-light conditions. A low-efficiency NPQ, characterized by weak NPQ induction capacity and a low level of protective NPQ, was observed in the marine angiosperm Zostera marina, which inhabits the shallow water regions. Furthermore, chlorophyll fluorescence and Western blot analysis verified that the fast-inducted component of NPQ, i.e., the energy-dependent quenching (qE), was not present in this species. In contrast with the lack of PSII antenna quenching sites for qE induction in brown algae and the lack of functional XC in Ulvophyceae belonging to green algae, all the antenna proteins and the functional XC are present in Z. marina. A novel underlying mechanism was observed that the limited construction of the trans-thylakoid proton gradient (ΔpH) caused by photoinactivation of the oxygen evolving complex (OEC) did not induce protonation of PsbS, thus explaining the inability to form quenching sites for qE induction. Although the ΔpH established under light exposure activated violaxanthin (V) de-epoxidase enzyme to catalyze conversion of V via antheraxanthin (A) and then to zeaxanthin (Z), the quenching capacity of de-epoxidized pigment was weak in Z. marina. We suggest that the low-efficiency NPQ was conducive to efficiently utilize the limited electrons to perform photosynthesis, resisting the adverse effect of OEC photoinactivation on the photosynthetic rate.
光系统 II（PSII）荧光的非光化学猝灭（NPQ）是使光养生物在高光条件下生存的最重要的保护机制之一。海洋被子植物海菖蒲（Zostera marina）表现出一种低效率的 NPQ，其特征为 NPQ 诱导能力弱和保护型 NPQ 水平低。此外，叶绿素荧光和 Western blot 分析证实，该物种不存在 NPQ 的快速诱导组分，即能量依赖型猝灭（qE）。与褐藻中 PSII 天线淬灭位点缺乏 qE 诱导以及绿藻中的 Ulvophyceae 中缺乏功能性 XC 不同，所有天线蛋白和功能性 XC 都存在于海菖蒲中。观察到一个新的潜在机制，即由于氧释放复合体（OEC）的光灭活导致的跨类囊体质子梯度（ΔpH）的有限构建，不会引起 PsbS 的质子化，从而解释了不能形成 qE 诱导的淬灭位点的原因。尽管在光暴露下建立的 ΔpH 激活了 violaxanthin（V）去环氧化酶，通过 antheraxanthin（A）催化 V 的转化，然后转化为 zeaxanthin（Z），但海菖蒲中去环氧化色素的猝灭能力较弱。我们认为，低效率的 NPQ 有利于有效地利用有限的电子进行光合作用，抵抗 OEC 光灭活对光合速率的不利影响。
