Thin-section electron micrograph of higher-plant chloroplast.
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Small-angle neutron scattering SANS is a non-invasive technique that can monitor dynamic structural parameters of the membrane system, such as the repeat distance, or the periodicity of thylakoid membranes. SANS studies on a large variety of photosynthetic organisms in vivo and isolated thylakoid membranes under a broad range of experimental conditions revealed unexpectedly high structural flexibility of the membrane system.
Figure 2. The light-harvesting functions of the thylakoid membrane depend on the molecular organization of LHCII — changes in the LHCII conformation and intermolecular interactions balance the amount of energy directed to the PSII reaction centers or dissipated as heat. The high degree of connectivity, i. Similar mechanisms seem to operate in diatoms, which have very different antenna organization Miloslavina et al. These processes are tightly regulated by interactions between the pigment-protein complexes in the membranes.
Extracting of the complexes from the membrane and solubilization with detergents perturbs the native structure. The anisotropic CD ACD of macroscopically aligned samples — an extension of the CD spectroscopy — provides additional information about the molecular orientation of the participating pigment dipoles.
For example, we have applied ACD to validate the structural model of the bacterial chlorosome baseplate protein CsmA Nielsen et al. Electrostatic interactions between LHCIIs mediated by charge-screening cations , are partly responsible for the stacking of thylakoid membranes and the formation of grana.
This effect is attributed to the so-called thermo-optic effect, a novel mechanism, discovered in our laboratory for review, see Garab Figure 3 — elementary structural changes in light-harvesting antenna complexes, elicited by local heat transients due to the dissipation of photon energy Gulbinas et al. In general, our knowledge about the mechanisms and effects of the dissipation of excess excitation energy in photosynthesis is quite rudimentary. A reconstituted Ni-bacterochlorophyll-containing bacterial antenna complex, with well-defined dissipation site and time, has thus been constructed Lambrev et al.
Figure 3. Thermo-optic effect in thylakoid membranes. Light-induced dark-reversible structural changes in the macroorganization of isolated thylakoid membranes monitored by amplitude variations of the psi-type CD band at nm. Schematic representation of the proposed three-state model for explaining the thermo-optic mechanism and the temperature-dependence of thermo-optically induced reorganizations.
Crystal structure of LHCII monomer illustrating the proximity of the site of dissipation red chlorophylls to the N-terminal region of the protein, possessing high flexibility and the ability to bind cations. Schematic model of the cation-assisted stacking of membrane layers in dark conditions and the thermo-optically induced cation release and concomitant membrane unstacking under light irradiation. As experimental systems of intermediate complexity bridging the gap between the full thylakoid membrane and isolated complexes, we use artificially reconstituted membrane models —proteoliposomes and supported lipid bilayers — containing predefined composition of lipids, protein complexes and cofactors.
With the help of these models we can mimic and understand various functions of the native photosynthetic membranes. Figure 4. Reconstituted thylakoid membrane models. In the past years, using P 31 -NMR and fluorescence spectroscopy, we provided experimental evidence supporting this hypothesis Krumova et al. We transform confocal laser scanning microscopes LSMs into differential-polarization DP- LSMs, which, via measuring pixel-by-pixel different physical quantities allow the mapping of anisotropic molecular organization of biological samples.
For papers, exhibitions and prizes, and patents see www. Akhtar, P. Pigment interactions in light-harvesting complex II in different molecular environments, J. Excitation energy transfer between light-harvesting complex II and Photosystem I in reconstituted membranes, Biochim. Acta Two-dimensional spectroscopy of chlorophyll a excited-state equilibration in light-harvesting complex II.
Demmig-Adams, B. Garab, G. Plant Biol. Hierarchical organization and structural flexibility of thylakoid membranes. Role of MGDG and non-bilayer lipid phases in the structure and dynamics of chloroplast thylakoid membranes. Lipids in Plant and Algae Dev. Ghazaryan, A. Involvement of the Lhcx protein Fcp6 of the diatom Cyclotella meneghiniana in the macro-organisation and structural flexibility of thylakoid membranes. Gulbinas, V. Biochemistry Herdean, A. A voltage-dependent chloride channel fine-tunes photosynthesis in plants, Nat. Hind, G.
Membrane crystals of plant light-harvesting complex II disassemble reversibly in light. Plant Cell Physiol. Govindjee, editor. Bibliography Includes bibliographical references and index.
Dynamic feedback of the photosystem II reaction centre on photoprotection in plants | Nature Plants
Contents From the Series Editors. Papageorgiou, Govindjee. Ostroumov et al.
Holzwarth, Peter Jahns. Kruger et al.
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Non-Photochemical Quenching and Energy Dissipation in Plants, Algae and Cyanobacteria
Adams III et al. Murchie, Jeremy Harbinson. Photosynthesis depends on photoprotection against intense sunlight, starting with the safe removal of excess excitation energy from the light-harvesting system, which can be quickly and non-destructively assessed via non-photochemical quenching of chlorophyll fluorescence NPQ. By placing NPQ into the context of whole-organism function, this book aims to contribute towards identification of plant and algal lines with superior stress resistance and productivity.
By addressing agreements and open questions concerning photoprotection's molecular mechanisms, this book contributes towards development of artificial photosynthetic systems. A comprehensive picture -from single molecules to organisms in ecosystems, and from leading expert's views to practical information for non-specialists on NPQ measurement and terminology - is presented. Bibliographic information. Publication date Series Advances in photosynthesis and respiration ; v. Browse related items Start at call number: QK N66 Librarian view Catkey: