Institute of Biological Chemistry, Washington State University, PO Box 646340, Pullman, WA, 99164-6340, USA.
Franceschi Microscopy and Imaging Center, Washington State University, Pullman, WA, 99164, USA.
Plant J. 2019 Feb;97(3):412-429. doi: 10.1111/tpj.14127. Epub 2018 Nov 9.
In plants, the stacking of part of the photosynthetic thylakoid membrane generates two main subcompartments: the stacked grana core and unstacked stroma lamellae. However, a third distinct domain, the grana margin, has been postulated but its structural and functional identity remains elusive. Here, an optimized thylakoid fragmentation procedure combined with detailed ultrastructural, biochemical, and functional analyses reveals the distinct composition of grana margins. It is enriched with lipids, cytochrome b f complex, and ATPase while depleted in photosystems and light-harvesting complexes. A quantitative method is introduced that is based on Blue Native Polyacrylamide Gel Electrophoresis (BN-PAGE) and dot immunoblotting for quantifying various photosystem II (PSII) assembly forms in different thylakoid subcompartments. The results indicate that the grana margin functions as a degradation and disassembly zone for photodamaged PSII. In contrast, the stacked grana core region contains fully assembled and functional PSII holocomplexes. The stroma lamellae, finally, contain monomeric PSII as well as a significant fraction of dimeric holocomplexes that identify this membrane area as the PSII repair zone. This structural organization and the heterogeneous PSII distribution support the idea that the stacking of thylakoid membranes leads to a division of labor that establishes distinct membrane areas with specific functions.
在植物中，部分光合类囊体膜的堆叠产生了两个主要的亚区室：堆叠的基粒核心和未堆叠的基质片层。然而，人们推测存在第三个截然不同的区域，即基粒边缘，但它的结构和功能特性仍然难以捉摸。在这里，优化的类囊体片段化程序与详细的超微结构、生化和功能分析相结合，揭示了基粒边缘的独特组成。它富含脂质、细胞色素 b f 复合物和 ATP 酶，而 photosystems 和光捕获复合物则减少。引入了一种定量方法，该方法基于 Blue Native Polyacrylamide Gel Electrophoresis (BN-PAGE) 和斑点免疫印迹，用于定量不同类囊体亚区室中各种光系统 II (PSII) 组装形式。结果表明，基粒边缘是光损伤 PSII 的降解和拆卸区。相比之下，堆叠的基粒核心区域包含完全组装和功能齐全的 PSII 完整复合物。最后，基质片层含有单体 PSII 以及相当一部分二聚体完整复合物，这表明该膜区域是 PSII 修复区。这种结构组织和异质 PSII 分布支持这样一种观点，即类囊体膜的堆叠导致了分工的建立，从而形成了具有特定功能的不同膜区域。
