title: Modulation of the multilamellar membrane organization and of the chiral macrodomains in the diatom Phaeodactylum tricornutum revealed by small-angle neutron scattering and circular dichroism spectroscopy.
abstract: Diatoms possess effective photoprotection mechanisms, which may involve reorganizations in the photosynthetic machinery. We have shown earlier, by using circular dichroism (CD) spectroscopy, that in Phaeodactylum tricornutum the pigment-protein complexes are arranged into chiral macrodomains, which have been proposed to be associated with the multilamellar organization of the thylakoid membranes and shown to be capable of undergoing light-induced reversible reorganizations (Szabó et al. Photosynth Res 95:237, 2008). Recently, by using small-angle neutron scattering (SANS) on the same algal cells we have determined the repeat distances and revealed reversible light-induced reorganizations in the lamellar order of thylakoids (Nagy et al. Biochem J 436:225, 2011). In this study, we show that in moderately heat-treated samples, the weakening of the lamellar order is accompanied by the diminishment of the psi-type CD signal associated with the long-range chiral order of the chromophores (psi, polymer or salt-induced). Further, we show that the light-induced reversible increase in the psi-type CD is associated with swelling in the membrane system, with magnitudes larger in high light than in low light. In contrast, shrinkage of the membrane system, induced by sorbitol, brings about a decrease in the psi-type CD signal; this shrinkage also diminishes the non-photochemical quenching capability of the cells. These data shed light on the origin of the psi-type CD signal, and confirm that both CD spectroscopy and SANS provide valuable information on the macro-organization of the thylakoid membranes and their dynamic properties; these parameters are evidently of interest with regard to the photoprotection in whole algal cells.
authors: Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, P.O. Box 49, Budapest, 1215, Hungary.
authors: Gergely
authors: G
authors: Nagy
authors: Milán
authors: M
authors: Szabó
authors: Renáta
authors: R
authors: Unnep
authors: György
authors: G
authors: Káli
authors: Yuliya
authors: Y
authors: Miloslavina
authors: Petar H
authors: PH
authors: Lambrev
authors: Ottó
authors: O
authors: Zsiros
authors: Lionel
authors: L
authors: Porcar
authors: Peter
authors: P
authors: Timmins
authors: László
authors: L
authors: Rosta
authors: Győző
authors: G
authors: Garab
mesh_terms: D002734:Chlorophyll / Q000737:chemistry; D002942:Circular Dichroism; D017377:Diatoms / Q000737:chemistry*; D006358:Hot Temperature; D008027:Light; D008968:Molecular Conformation; D009502:Neutrons; D009994:Osmolar Concentration; D010788:Photosynthesis; D053838:Scattering, Small Angle; D020524:Thylakoids / Q000737:chemistry*; D013997:Time Factors
chemical_list: D002734:Chlorophyll