title: Monitoring thylakoid ultrastructural changes in vivo using small-angle neutron scattering.
abstract: 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.
authors.affiliation: Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, POB 49, H-1525 Budapest, Hungary.
authors.forename: Renáta
authors.initials: R
authors.lastname: Unnep
authors.affiliation: 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.
authors.forename: Gergely
authors.initials: G
authors.lastname: Nagy
authors.affiliation: 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.
authors.forename: Márton
authors.initials: M
authors.lastname: Markó
authors.affiliation: Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, POB 521, H-6701 Szeged, Hungary. Electronic address: garab.gyozo@brc.mta.hu.
authors.forename: Győző
authors.initials: G
authors.lastname: Garab
mesh_terms: D002736:Chloroplasts / Q000648:ultrastructure*; D000458:Cyanobacteria / Q000502:physiology / Q000528:radiation effects / Q000648:ultrastructure*; D017377:Diatoms / Q000502:physiology / Q000528:radiation effects / Q000648:ultrastructure*; D009154:Mutation; D033363:Neutron Diffraction / Q000379:methods*; D009502:Neutrons; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000648:ultrastructure*; D053838:Scattering, Small Angle; D020524:Thylakoids / Q000648:ultrastructure*
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins
keywords: Lamellar repeat distance; Light-induced ultrastructural changes; Photosynthesis; Small angle neutron scattering; Thylakoid membranes