Plant Physiol, July 2002, Vol. 129, pp. 1398-1406
Influence of the Diadinoxanthin Pool Size on Photoprotection in
the Marine Planktonic Diatom Phaeodactylum
tricornutum1
Johann
Lavaud,*
Bernard
Rousseau,
Hans J.
van Gorkom, and
Anne-Lise
Etienne
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 (J.L., B.R., A.-L.E.); and
Department of Biophysics, Huygens Laboratory, Leiden University, P.O.
Box 9504, 2300 RA Leiden, The Netherlands (H.J.v.G.)
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 (Fm, PSII reaction centers closed), which was fully reversed in the dark. The
non-photochemical quenching of the minimum fluorescence yield
(Fo, PSII centers open) decreased the
quantum efficiency of PSII proportionally. For both
Fm and Fo, the
non-photochemical quenching expressed as
F/F' 
1 (with F' the
quenched level) was proportional to the DT concentration. However, the
quenching of Fo relative to that of
Fm 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.
1
This work was supported by the French Ministry
of National Education, Research, and Technology (grant to J.L.) and by
the Ecole Normale Supérieure (invited professorship to
H.J.v.G.).
*
Corresponding author; e-mail lavaud{at}biologie.ens.fr; fax
33-1-44-32-3935.
© 2002 American Society of Plant Physiologists
