Influence of the diadinoxanthin pool size on photoprotection in the marine planktonic diatom Phaeodactylum tricornutum.
The pool size of the xanthophyll cycle pigment diadinoxanthin (DD) in the diatom Phaeodactylum tricornutum depends on illumination conditions during culture. Intermittent light caused a doubling of the DD pool without significant change in other pigment contents and photosynthetic parameters, including the photosystem II (PSII) antenna size. On exposure to high-light intensity, extensive de-epoxidation of DD to diatoxanthin (DT) rapidly caused a very strong quenching of the maximum chlorophyll fluorescence yield (F(m), PSII reaction centers closed), which was fully reversed in the dark. The non-photochemical quenching of the minimum fluorescence yield (F(o), PSII centers open) decreased the quantum efficiency of PSII proportionally. For both F(m) and F(o), the non-photochemical quenching expressed as F/F' - 1 (with F' the quenched level) was proportional to the DT concentration. However, the quenching of F(o) relative to that of F(m) was much stronger than random quenching in a homogeneous antenna could explain, showing that the rate of photochemical excitation trapping was limited by energy transfer to the reaction center rather than by charge separation. The cells can increase not only the amount of DT they can produce, but also its efficiency in competing with the PSII reaction center for excitation. The combined effect allowed intermittent light grown cells to down-regulate PSII by 90% and virtually eliminated photoinhibition by saturating light. The unusually rapid and effective photoprotection by the xanthophyll cycle in diatoms may help to explain their dominance in turbulent waters.
Lavaud
Johann
J
Laboratoire Organismes Photosynthétiques et Environnement, Unité Mixte de Recherche-Centre National de la Recherche Scientifique 8543, Ecole Normale Supérieure, 46 rue d'Ulm, 75230 Paris cedex 05, France. lavaud@biologie.ens.fr
Rousseau
Bernard
B
van Gorkom
Hans J
HJ
Etienne
Anne-Lise
AL
D000465:Algorithms; D002734:Chlorophyll / Q000378:metabolism; D017377:Diatoms / Q000502:physiology* / Q000528:radiation effects; D005453:Fluorescence; D008027:Light; D045342:Light-Harvesting Protein Complexes; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology* / Q000528:radiation effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism / Q000528:radiation effects; D045332:Photosystem II Protein Complex; D010839:Phytoplankton / Q000502:physiology* / Q000528:radiation effects; D024341:Xanthophylls / Q000378:metabolism* / Q000528:radiation effects
D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D024341:Xanthophylls; D002734:Chlorophyll; C033808:diadinoxanthin; D010100:Oxygen