title: Characterization of the structural changes and photochemical activity of photosystem I under Al(3+) effect.
abstract: The photochemical activity of photosystem I (PSI) as affected by Al(3+) was investigated in thylakoid membranes and PSI submembrane fractions isolated from spinach. Biophysical and biochemical techniques such as oxygen uptake, light induced absorbance changes at 820nm, chlorophyll fluorescence emission, SDS-polyacrylamide gel electrophoresis, and FTIR spectroscopy have been used to analyze the sites and action modes of this cation on the PSI complex. Our results showed that Al(3+) above 3mM induces changes in the redox state of P700 reflected by an increase of P700 photooxidation phase and a delay of the slower rate of P700 re-reduction which reveals that Al(3+) exerted an inhibitory action at the donor side of PSI especially at plastocyanin (PC). Furthermore, results of P700 photooxidation monitored in the presence of DCMU with or without MV suggested that the same range of Al(3+) concentrations impairs the photochemical reaction centers (RC) of PSI, as shown by the decline in the amount of active population of P700, and disrupts the charge separation between P700 and the primary electron acceptor A0 leading to the inhibition of electron transfer at the acceptor side of PSI. These inhibitory actions were also accompanied by an impairment of the energy transfer from light harvesting complex (LHCI) to RC of PSI, following the disconnection of LHCI antenna as illustrated by an enhancement of chlorophyll fluorescence emission spectra at low temperature (77K). The above results coincided with FTIR measurements that indicated a conformational change of the protein secondary structures in PSI complex where 25% of α-helix was converted into β-sheet, β-antiparallel and turn structures. These structural changes in PSI complex proteins are closely related with the alteration photochemical activity of PSI including the inhibition of the electron transport through both acceptor and donor sides of PSI.
authors.affiliation: Groupe de Recherche en Biologie Végétale, Département de Chimie, Biochimie et Physique, Université du Québec à Trois-Rivières, Trois-Rivières, Qc G9A 5H7, Canada.
authors.forename: Imed
authors.initials: I
authors.lastname: Hasni
authors.affiliation: Laboratory of Physiology and Biochemistry of Salt Tolerance in Plants, Faculty of Sciences of Tunis, Campus University, 1060, Tunisia.
authors.forename: Najoua
authors.initials: N
authors.lastname: Msilini
authors.affiliation: Plant Systems Biology Group, Partner Institute of Computational Biology, Chinese Academy of Sciences, Shanghai 200031, China.
authors.forename: Saber
authors.initials: S
authors.lastname: Hamdani
authors.affiliation: Groupe de Recherche en Biologie Végétale, Département de Chimie, Biochimie et Physique, Université du Québec à Trois-Rivières, Trois-Rivières, Qc G9A 5H7, Canada.
authors.forename: Heidar-Ali
authors.initials: HA
authors.lastname: Tajmir-Riahi
authors.affiliation: Groupe de Recherche en Biologie Végétale, Département de Chimie, Biochimie et Physique, Université du Québec à Trois-Rivières, Trois-Rivières, Qc G9A 5H7, Canada. Electronic address: Robert.Carpentier@uqtr.ca.
authors.forename: Robert
authors.initials: R
authors.lastname: Carpentier
mesh_terms: D000535:Aluminum / Q000378:metabolism / Q000633:toxicity*; D001692:Biological Transport / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004579:Electron Transport / Q000187:drug effects; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D055668:Photochemical Processes / Q000187:drug effects*; D045331:Photosystem I Protein Complex / Q000737:chemistry* / Q000378:metabolism; D018724:Spinacia oleracea / Q000166:cytology; D020524:Thylakoids / Q000187:drug effects / Q000378:metabolism
chemical_list: D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex; D000535:Aluminum; D010100:Oxygen
keywords: Aluminum; Light harvesting complex I; Oxygen uptake activity; P700; Photosystem I; Protein secondary structure