Research article

Lutein is needed for efficient chlorophyll triplet quenching in the major LHCII antenna complex of higher plants and effective photoprotection in vivo under strong light

Luca Dall'Osto¹ , Chiara Lico² , Jean Alric^4,5 , Giovanni Giuliano² , Michel Havaux³ and Roberto Bassi^1,4

¹  Dipartimento Scientifico e Tecnologico, Università di Verona, Strada Le Grazie 15, I-37134 Verona, Italy

²  Ente per le Nuove tecnologie, l'Energia e l'Ambiente (ENEA), Unità Biotecnologie, Centro Ricerche Casaccia, C.P. 2400, Roma 00100, Italy

³  CEA/Cadarache, DSV, DEVM, Laboratoire d'Ecophysiologie de la Photosynthèse, UMR 6191 CEA-CNRS-Aix Marseille II, F-13108 Saint-Paul-lez-Durance, France

⁴  Laboratoire de Génétique et Biophysique des Plantes (LGBP), Département d'Ecophysiologie Végétale et Microbiologie – UMR 163 CEA-CNRS Université de la Méditerranée Aix-Marseille II, 163 Avenue de Luminy, Marseille, France

⁵  Institut de Biologie Physico-Chimique (IBPC), rue Pierre et Marie Curie 13, Paris, France

author email corresponding author email

BMC Plant Biology 2006, 6:32doi:10.1186/1471-2229-6-32

Published:	27 December 2006

Abstract

Background

Lutein is the most abundant xanthophyll in the photosynthetic apparatus of higher plants. It binds to site L1 of all Lhc proteins, whose occupancy is indispensable for protein folding and quenching chlorophyll triplets. Thus, the lack of a visible phenotype in mutants lacking lutein has been surprising.

Results

We have re-assessed the lut2.1 phenotypes through biochemical and spectroscopic methods. Lhc proteins from the lut2.1 mutant compensate the lack of lutein by binding violaxanthin in sites L1 and L2. This substitution reduces the capacity for regulatory mechanisms such as NPQ, reduces antenna size, induces the compensatory synthesis of Antheraxanthin + Zeaxanthin, and prevents the trimerization of LHCII complexes. In vitro reconstitution shows that the lack of lutein per se is sufficient to prevent trimerization. lut2.1 showed a reduced capacity for state I – state II transitions, a selective degradation of Lhcb1 and 2, and a higher level of photodamage in high light and/or low temperature, suggesting that violaxanthin cannot fully restore chlorophyll triplet quenching. In vitro photobleaching experiments and time-resolved spectroscopy of carotenoid triplet formation confirmed this hypothesis. The npq1lut2.1 double mutant, lacking both zeaxanthin and lutein, is highly susceptible to light stress.

Conclusion

Lutein has the specific property of quenching harmful ³Chl* by binding at site L1 of the major LHCII complex and of other Lhc proteins of plants, thus preventing ROS formation. Substitution of lutein by violaxanthin decreases the efficiency of ³Chl* quenching and causes higher ROS yield. The phenotype of lut2.1 mutant in low light is weak only because rescuing mechanisms of photoprotection, namely zeaxanthin synthesis, compensate for the ROS production. We conclude that zeaxanthin is effective in photoprotection of plants lacking lutein due to the multiple effects of zeaxanthin in photoprotection, including ROS scavenging and direct quenching of Chl fluorescence by binding to the L2 allosteric site of Lhc proteins.