title: Transversal and lateral exciton energy transfer in grana thylakoids of spinach.
abstract: The excitation energy transfer between photosystem (PS) II complexes was studied in isolated grana disks and thylakoids using chlorophyll a fluorescence induction measurements in the presence of DCMU under stacked and destacked conditions. Destacking of grana was achieved using a sonication protocol in a buffer without MgCl(2). The degree of stacking was controlled and quantified by atomic force microscopy and by the concomitant absorption changes. As expected from the literature, intact thylakoids showed a strong dependency of the connectivity of PSII centers, the F(m)/F(o) ratio as well as the fraction of PSIIbeta centers on the MgCl(2) concentration. In contrast, these parameters did not change in isolated grana disks. In particular, the connectivity remained constantly high irrespective of the degree of destacking. These differences were explained by the high protein density in grana disks, which hinders separation and mixing of proteins sufficiently to change energy transfer properties. Due to the occurrence of stroma lamella in intact thylakoids, intermixing of PSII and PSI is possible and allows for changes in F(m)/F(o) ratio as is the separation of LHCII from PSII, thus leading to an increase in the fraction of PSIIbeta. Even if mixing and separation of proteins are impaired in isolated grana disks, destacking should lead to a decrease in connectivity if transversal excitation energy transfer between two opposite membranes is significant. Because the connectivity is constant over all degrees of destacking employed, we conclude that the energy transfer in granas is mainly lateral.
authors.affiliation: Institut für Botanik, Schlossgarten 3, Wilhelm-Klemm-Strasse 10, D-48149 Münster, Germany. kirchhh@uni-muenster.de
authors.forename: Helmut
authors.initials: H
authors.lastname: Kirchhoff
authors.forename: Mauricio
authors.initials: M
authors.lastname: Borinski
authors.forename: Steven
authors.initials: S
authors.lastname: Lenhert
authors.forename: Lifeng
authors.initials: L
authors.lastname: Chi
authors.forename: Claudia
authors.initials: C
authors.lastname: Büchel
mesh_terms: D002734:Chlorophyll / Q000737:chemistry; D000077194:Chlorophyll A; D004735:Energy Transfer; D005470:Fluorometry; D008051:Lipid Bilayers / Q000737:chemistry; D015636:Magnesium Chloride / Q000737:chemistry; D018625:Microscopy, Atomic Force; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism; D013010:Sonication; D013053:Spectrophotometry; D018724:Spinacia oleracea / Q000737:chemistry* / Q000378:metabolism; D020524:Thylakoids / Q000737:chemistry* / Q000378:metabolism
chemical_list: D008051:Lipid Bilayers; D045332:Photosystem II Protein Complex; D015636:Magnesium Chloride; D002734:Chlorophyll; C037184:chlorophyll b; D000077194:Chlorophyll A