Proper assembly of plant photosystem II, in the appressed region of thylakoids, allows for both efficient light harvesting and the dissipation of excitation energy absorbed in excess. The core moiety of wild type supercomplex is associated with monomeric antennae that, in turn, bind peripheral trimeric LHCII complexes. Acclimation to light environment dynamics involves structural plasticity within PSII-LHCs supercomplexes, including depletion in LHCII and CP24. Here, we report on the acclimation of NoM, an Arabidopsis mutant lacking monomeric LHCs but retaining LHCII trimer. Lack of monomeric LHCs impaired the operation of both photosynthetic electron transport and state transitions, despite the fact that NoM underwent a compensatory over-accumulation of the LHCII complement compared to the wild type. Mutant plants displayed stunted growth compared to the wild type when probed over a range of light conditions. When exposed to short-term excess light, NoM showed higher photosensitivity and enhanced singlet oxygen release than the wild type, whereas long-term acclimation under stress conditions was unaffected. Analysis of pigment-binding supercomplexes showed that the absence of monomeric LHCs did affect the macro-organisation of photosystems: large PSI-LHCII megacomplexes were more abundant in NoM, whereas the assembly of PSII-LHCs supercomplexes was impaired. Observation by electron microscopy (EM) and image analysis of thylakoids highlighted impaired granal stacking and membrane organisation, with a heterogeneous distribution of PSII and LHCII compared to the wild type. It is concluded that monomeric LHCs are critical for the structural and functional optimisation of the photosynthetic apparatus.

中文翻译：

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单体光收集复合物增强了从LHCII到PSII的激发能转移，并控制了类囊体中的横向间距。

在拟南芥的贴壁区域中，植物光系统II的正确组装可实现有效的光收集和多余吸收的激发能的消散。野生型超复合物的核心部分与单体触角相关，而单体触角又结合了外围的三聚体LHCII复合物。适应光照环境动力学涉及PSII-LHCs超复合物内部的结构可塑性，包括LHCII和CP24的耗竭。在这里，我们报告了NoM的适应性，NoM是一种缺乏单体LHCs但保留LHCII三聚体的拟南芥突变体。单体LHC的缺乏削弱了光合电子传递和状态转换的运行，尽管与野生型相比NoM经历了LHCII补体的补偿性过度积累。在一定范围的光照条件下进行探测时，与野生型植物相比，突变型植物的生长发育迟缓。当暴露于短期过量光下时，NoM较野生型表现出更高的光敏性和增强的单线态氧释放，而在胁迫条件下的长期适应却不受影响。对色素结合超复合物的分析表明，单体LHC的缺失确实会影响光系统的宏观组织：NoM中的大型PSI-LHCII巨型复合物更为丰富，而PSII-LHCs超复合物的组装受到损害。电镜观察和类囊体图像分析突出显示了颗粒堆积和膜组织受损，与野生型相比，PSII和LHCII分布不均。