Unnep Renáta, Nagy Gergely, Markó Márton, Garab Győző
Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, POB 49, H-1525 Budapest, Hungary.
Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, POB 49, H-1525 Budapest, Hungary; Laboratory for Neutron Scattering, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland.
Plant Physiol Biochem. 2014 Aug;81:197-207. doi: 10.1016/j.plaphy.2014.02.005. Epub 2014 Feb 18.
The light reactions of oxygenic photosynthesis take place in the thylakoid membranes, flattened vesicles, which contain the two photosystems and also embed the cytochrome b6f complex and the ATP synthase. In general, the thylakoid membranes are assembled into multilamellar membrane systems, which warrant an optimal light capturing efficiency. In nature, they show astounding variations, primarily due to large variations in their protein composition, which is controlled by multilevel regulatory mechanisms during long-term acclimation and short-term adaptation processes and also influenced by biotic or abiotic stresses - indicating a substantial degree of flexibility in the membrane ultrastructure. The better understanding of the dynamic features of this membrane system requires the use of non-invasive techniques, such as small angle neutron scattering (SANS), which is capable of providing accurate, statistically and spatially averaged information on the repeat distances of periodically organized thylakoid membranes under physiologically relevant conditions with time resolutions of seconds and minutes. In this review, after a short section on the basic properties of neutrons, we outline the fundamental principles of SANS measurements, its strengths and weaknesses in comparison to complementary structure investigation techniques. Then we overview recent results on isolated plant thylakoid membranes, and on living cyanobacterial and algal cells as well as on whole leaves. Special attention is paid to light-induced reversible ultrastructural changes in vivo, which, in cyanobacterial and diatom cells, were uncovered with the aid of SANS measurements; we also discuss the role of membrane reorganizations in light adaptation and photoprotection mechanisms.
氧光合作用的光反应发生在类囊体膜中，类囊体膜是扁平的囊泡，其中包含两个光系统，还嵌入了细胞色素b6f复合体和ATP合酶。一般来说，类囊体膜组装成多层膜系统，以保证最佳的光捕获效率。在自然界中，它们表现出惊人的变化，主要是由于其蛋白质组成的巨大差异，这种差异在长期适应和短期适应过程中受到多级调节机制的控制，并且还受到生物或非生物胁迫的影响——这表明膜超微结构具有很大程度的灵活性。要更好地理解这个膜系统的动态特征，需要使用非侵入性技术，如小角中子散射（SANS），它能够在生理相关条件下，以秒和分钟的时间分辨率，提供关于周期性组织的类囊体膜重复距离的准确、统计和空间平均信息。在这篇综述中，在简短介绍中子的基本特性之后，我们概述了SANS测量的基本原理，以及与互补结构研究技术相比它的优缺点。然后我们综述了关于分离的植物类囊体膜、活的蓝细菌和藻类细胞以及整片叶子的最新研究结果。特别关注体内光诱导的可逆超微结构变化，在蓝细菌和硅藻细胞中，这些变化是借助SANS测量发现的；我们还讨论了膜重组在光适应和光保护机制中的作用。
