Three-Dimensional Architecture of Grana and Stroma Thylakoids of Higher Plants as Determined by Electron Tomography
Three-Dimensional Architecture of Grana and Stroma Thylakoids of Higher Plants as Determined by Electron Tomography
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DOI：
10.1104/pp.110.170647
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发表时间：
2011-04-01
期刊：
影响因子：
7.4
通讯作者：
Staehelin, L. Andrew
中科院分区：
文献类型：
--
作者：
Austin, Jotham R., II;Staehelin, L. Andrew
我们用高压冷冻/冷冻取代完整叶绿体的电子断层扫描技术研究了拟南芥、烟草和菠菜类囊体膜的三维(3D)结构，分辨率约为7 nm。高等植物类囊体被分化为两个相互关联且功能截然不同的结构域，即富含光系统II/捕光复合体II的堆叠基粒类囊体和富含光系统I/ATP合酶的非堆叠基质类囊体。基粒类囊体以圆柱状堆叠的形式组织，并通过管状连接与基质类囊体相连。我们的数据证实，基质类囊体以螺旋状的多个右旋螺旋的形式缠绕在基粒堆叠的周围，其角度为20度到25度，如螺旋类囊模型所假设的那样。基粒和基质类囊体之间的连接都具有狭缝状结构，但它们的大小差异很大，从大约15×30 nm到大约15×435 nm，大约是化学固定类囊体大5倍。变狭缝长度导致基粒/基质类囊体组织中的周期性比原始螺旋模型中所提出的要小。基质类囊体也表现出相当大的结构多样性，这在一定程度上取决于它们所连接的相邻基粒堆叠的数量和方向。一些基质类囊体在相邻的基粒之间形成实心的片状桥梁，而另一些则表现出分支几何形状，小的、更管状的片状域也连接相邻的平行基质类囊体。我们推测，连接缝隙大小的巨大变化可能反映了连接缝隙在光合作用功能调节中的一种新的、积极的作用。特别是，通过控制连接缝隙的大小，植物可以调节离子和膜分子在基粒和基质类囊体膜结构域之间的流动。
We have investigated the three-dimensional (3D) architecture of the thylakoid membranes of Arabidopsis (Arabidopsis thaliana), tobacco (Nicotiana tabacum), and spinach (Spinacia oleracea) with a resolution of approximately 7 nm by electron tomography of high-pressure-frozen/freeze-substituted intact chloroplasts. Higher-plant thylakoids are differentiated into two interconnected and functionally distinct domains, the photosystem II/light-harvesting complex II-enriched stacked grana thylakoids and the photosystem I/ATP synthase-enriched, nonstacked stroma thylakoids. The grana thylakoids are organized in the form of cylindrical stacks and are connected to the stroma thylakoids via tubular junctions. Our data confirm that the stroma thylakoids are wound around the grana stacks in the form of multiple, right-handed helices at an angle of 20 degrees to 25 degrees as postulated by a helical thylakoid model. The junctional connections between the grana and stroma thylakoids all have a slit-like architecture, but their size varies tremendously from approximately 15 x 30 nm to approximately 15 x 435 nm, which is approximately 5 times larger than seen in chemically fixed thylakoids. The variable slit length results in less periodicity in grana/stroma thylakoid organization than proposed in the original helical model. The stroma thylakoids also exhibit considerable architectural variability, which is dependent, in part, on the number and the orientation of adjacent grana stacks to which they are connected. Whereas some stroma thylakoids form solid, sheet-like bridges between adjacent grana, others exhibit a branching geometry with small, more tubular sheet domains also connecting adjacent, parallel stroma thylakoids. We postulate that the tremendous variability in size of the junctional slits may reflect a novel, active role of junctional slits in the regulation of photosynthetic function. In particular, by controlling the size of junctional slits, plants could regulate the flow of ions and membrane molecules between grana and stroma thylakoid membrane domains.