Zostera marina, a fully submerged marine angiosperm with a unique evolutionary history associated with its terrestrial origin, has distinct photochemical characteristics caused by its oxygen-evolving complex (OEC) being prone to deactivation in visible light. Based on the present phylogenetic analysis, the chloroplast NADPH dehydrogenase-like (NDH) complex was found to be completed in of Z. marina, unlike other marine plants, suggesting its crucial role. Thus, the responses of electron transport to irradiation were investigated through multiple chlorophyll fluorescence techniques and Western blot analysis. Moreover, the respective contribution of the two photosystem I cyclic electron flow (PSI-CEF) pathways to the generation of trans-thylakoid proton gradient (∆pH) was also examined using inhibitors. The contributions of the two PSI-CEF pathways to ∆pH were similar; furthermore, there was a trade-off between the two pathways under excess irradiation: the PGR5/L1-dependent PSI-CEF decreased gradually following its activation during the initial illumination, while NDH-dependent PSI-CEF was activated gradually with exposure duration. OEC inactivation was continuously under excess irradiation, which exhibits a positive linear correlation with the activation of NDH-dependent PSI-CEF. We suggest that PGR5/L1-dependent PSI-CEF was preferentially activated to handle the excess electron caused by the operation of OEC during the initial illumination. Subsequently, the increasing OEC inactivation with exposure duration resulted in a deficit of electrons. Limited electrons from PSI might preferentially synthesize NADPH, which could support the function of NDH-dependent PSI-CEF to generate ∆pH and ATP via reducing ferredoxin, thereby maintaining OEC stability.

Zostera marina是一种完全淹没的海洋被子植物，具有与其陆地起源相关的独特进化历史，由于其析氧复合物 (OEC) 在可见光下易于失活，因此具有独特的光化学特征。基于目前的系统发育分析，发现叶绿体 NADPH 脱氢酶样 (NDH) 复合物在Z. marina中完成，与其他海洋植物不同，表明其至关重要的作用。因此，通过多种叶绿素荧光技术和蛋白质印迹分析研究了电子传递对辐射的响应。此外，还使用抑制剂检查了两个光系统 I 循环电子流 (PSI-CEF) 途径对产生反式类囊体质子梯度 (ΔpH) 的各自贡献。两种 PSI-CEF 途径对 ΔpH 的贡献相似；此外，在过度照射下，两种途径之间存在权衡：PGR5/L1 依赖性 PSI-CEF 在初始光照期间激活后逐渐下降，而 NDH 依赖性 PSI-CEF 随着暴露时间逐渐激活。OEC在过度照射下持续失活，它与 NDH 依赖性 PSI-CEF 的激活呈正线性相关。我们建议优先激活 PGR5/L1 依赖性 PSI-CEF 以处理在初始照明期间由 OEC 操作引起的过量电子。随后，随着暴露时间的增加，OEC 失活的增加导致电子不足。来自 PSI 的有限电子可能优先合成 NADPH，这可以支持 NDH 依赖性 PSI-CEF 通过还原铁氧还蛋白产生 ΔpH 和 ATP 的功能，从而维持 OEC 稳定性。随着暴露时间增加OEC失活导致电子不足。来自 PSI 的有限电子可能优先合成 NADPH，这可以支持 NDH 依赖性 PSI-CEF 通过还原铁氧还蛋白产生 ΔpH 和 ATP 的功能，从而维持 OEC 稳定性。随着暴露时间增加OEC失活导致电子不足。来自 PSI 的有限电子可能优先合成 NADPH，这可以支持 NDH 依赖性 PSI-CEF 通过还原铁氧还蛋白产生 ΔpH 和 ATP 的功能，从而维持 OEC 稳定性。