title: Chlorophyll triplet states associated with Photosystem I and Photosystem II in thylakoids of the green alga Chlamydomonas reinhardtii.
abstract: The analysis of FDMR spectra, recorded at multiple emission wavelengths, by a global decomposition technique, has allowed us to characterise the triplet populations associated with Photosystem I and Photosystem II of thylakoids in the green alga Chlamydomonas reinhardtii. Three triplet populations are observed at fluorescence emissions characteristic of Photosystem II, and their zero field splitting parameters have been determined. These are similar to the zero field parameters for the three Photosystem II triplets previously reported for spinach thylakoids, suggesting that they have a widespread occurrence in nature. None of these triplets have the zero field splitting parameters characteristic of the Photosystem II recombination triplet observed only under reducing conditions. Because these triplets are generated under non-reducing redox conditions, when the recombination triplet is undetectable, it is suggested that they may be involved in the photoinhibition of Photosystem II. At emission wavelengths characteristic of Photosystem I, three triplet populations are observed, two of which are attributed to the P(700) recombination triplet frozen in two different conformations, based on the microwave-induced fluorescence emission spectra and the triplet minus singlet difference spectra. The third triplet population detected at Photosystem I emission wavelengths, which was previously unresolved, is proposed to originate from the antenna chlorophyll of the core or the unusually blue-shifted outer antenna complexes of this organism.
authors.affiliation: Centre for Fundamental Research in Photosynthesis, Hendon, 67 The Burroughs, London NW4 4AX, UK. s.santabarbara@qmul.ac.uk <s.santabarbara@qmul.ac.uk>
authors.forename: Stefano
authors.initials: S
authors.lastname: Santabarbara
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Agostini
authors.forename: Anna Paola
authors.initials: AP
authors.lastname: Casazza
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Syme
authors.forename: P
authors.initials: P
authors.lastname: Heathcote
authors.forename: Felix
authors.initials: F
authors.lastname: Böhles
authors.forename: Michael C W
authors.initials: MC
authors.lastname: Evans
authors.forename: Robert C
authors.initials: RC
authors.lastname: Jennings
authors.forename: Donatella
authors.initials: D
authors.lastname: Carbonera
mesh_terms: D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000737:chemistry*; D002734:Chlorophyll / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular; D045331:Photosystem I Protein Complex / Q000737:chemistry*; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D020524:Thylakoids / Q000737:chemistry*
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D002734:Chlorophyll