title: The extraordinary longevity of kleptoplasts derived from the Ross Sea haptophyte Phaeocystis antarctica within dinoflagellate host cells relates to the diminished role of the oxygen-evolving Photosystem II and to supplementary light harvesting by mycosporine-like amino acid/s.
abstract: The haptophyte Phaeocystis antarctica and the novel Ross Sea dinoflagellate that hosts kleptoplasts derived from P. antarctica (RSD; R.J. Gast et al., 2006, J. Phycol. 42 233-242) were compared for photosynthetic light harvesting and for oxygen evolution activity. Both chloroplasts and kleptoplasts emit chlorophyll a (Chl a) fluorescence peaking at 683nm (F683) at 277K and at 689 (F689) at 77K. Second derivative analysis of the F689 band at 77K revealed two individual contributions centered at 683nm (Fi-683) and at 689 (Fi-689). Using the p-nitrothiophenol (p-NTP) treatment of Kobayashi et al. (Biochim. Biophys. Acta 423 (1976) 80-90) to differentiate between Photosystem (PS) II and I fluorescence emissions, we could identify PS II as the origin of Fi-683and PS I as the origin of Fi-689. Both emissions could be excited not only by Chl a-selective light (436nm) but also by mycosporine-like amino acids (MAAs)-selective light (345nm). This suggests that a fraction of MAAs must be proximal to Chls a and, therefore, located within the plastids. On the basis of second derivative fluorescence spectra at 77K, of p-NTP resolved fluorescence spectra, as well as of PSII-driven oxygen evolution activities, PS II appears substantially less active (~1/5) in dinoflagellate kleptoplasts than in P. antarctica chloroplasts. We suggest that a diminished role of PS II, a known source of reactive oxygen species, and a diminished dependence on nucleus-encoded light-harvesting proteins, due to supplementary light-harvesting by MAAs, may account for the extraordinary longevity of RSD kleptoplasts.
authors.affiliation: Institute of Biosciences and Applications, NCSR "Demokritos", Aghia Paraskevi, Attikis, Greece. Electronic address: kstam@bio.demokritos.gr.
authors.forename: Kostas
authors.initials: K
authors.lastname: Stamatakis
authors.affiliation: Institute of Biosciences and Applications, NCSR "Demokritos", Aghia Paraskevi, Attikis, Greece.
authors.forename: Dimitris
authors.initials: D
authors.lastname: Vayenos
authors.affiliation: Institute of Biosciences and Applications, NCSR "Demokritos", Aghia Paraskevi, Attikis, Greece; Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, Temesvári krt. 62, H-6726 Szeged, Hungary; Kontakeika, Karlovassi Samos, GR-83200, Greece.
authors.forename: Christos
authors.initials: C
authors.lastname: Kotakis
authors.affiliation: Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Gast
authors.affiliation: Institute of Biosciences and Applications, NCSR "Demokritos", Aghia Paraskevi, Attikis, Greece.
authors.forename: George C
authors.initials: GC
authors.lastname: Papageorgiou
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D000864:Antarctic Regions; D002734:Chlorophyll / Q000031:analogs & derivatives / Q000378:metabolism; D000077194:Chlorophyll A; D002736:Chloroplasts / Q000378:metabolism*; D004141:Dinoflagellida / Q000378:metabolism*; D005453:Fluorescence; D058087:Haptophyta / Q000378:metabolism*; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism*; D008136:Longevity / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D018087:Plastids / Q000378:metabolism
chemical_list: D000596:Amino Acids; D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; C085815:chlorophyll a'; D010100:Oxygen; D000077194:Chlorophyll A
keywords: Kleptoplast; Phaeocystis antarctica; Photosynthetic oxygen evolution; Photosystems I, II; Ross Sea dinoflagellate