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) 是最重要的保护机制之一，使向光生物能够在高光条件下存活。在栖息于浅水区的海洋被子植物Zostera marina 中观察到低效率的 NPQ，其特征是 NPQ 诱导能力弱和保护性 NPQ 水平低。此外，叶绿素荧光和蛋白质印迹分析证实 NPQ 的快速诱导成分，即能量依赖性淬灭 (qE)，在该物种中不存在。与褐藻中缺乏用于 qE 诱导的 PSII 天线淬灭位点和属于绿藻的绿藻科中缺乏功能性 XC 相比，所有的天线蛋白和功能性 XC 都存在于Z. 码头。观察到一种新的潜在机制，由析氧复合物 (OEC) 的光灭活引起的跨类囊体质子梯度 (ΔpH) 的有限构建不会诱导 PsbS 的质子化，从而解释了无法形成用于 qE 诱导的淬灭位点。尽管在光照下建立的 ΔpH 激活了紫黄质 (V) 脱环氧化酶以催化 V 通过花黄素 (A) 转化为玉米黄质 (Z)，但在Z. marina 中，脱环氧化色素的淬灭能力较弱。我们认为低效率的 NPQ 有利于有效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。