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BIOENERGETICS AND PHOTOSYNTHESIS

The Zeaxanthin-Independent and Zeaxanthin-Dependent qE Components of Nonphotochemical Quenching Involve Common Conformational Changes within the Photosystem II Antenna in Arabidopsis^1,[W]

School of Biological and Chemical Sciences, Queen Mary University of London, London E1 4NS, United Kingdom (M.P.J., A.Z., A.V.R.); and Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, United Kingdom (M.L.P.-B., P.H.)

The light-harvesting antenna of higher plant photosystem II (LHCII) has the intrinsic capacity to dissipate excess light energy as heat in a process termed nonphotochemical quenching (NPQ). Recent studies suggest that zeaxanthin and lutein both contribute to the rapidly relaxing component of NPQ, qE, possibly acting in the minor monomeric antenna complexes and the major trimeric LHCII, respectively. To distinguish whether zeaxanthin and lutein act independently as quenchers at separate sites, or alternatively whether zeaxanthin fulfills an allosteric role regulating lutein-mediated quenching, the kinetics of qE and the qE-related conformational changes (A₅₃₅) were compared in Arabidopsis (Arabidopsis thaliana) mutant/antisense plants with altered contents of minor antenna (kolhcb6, aslhcb4), trimeric LHCII (aslhcb2), lutein (lut2, lut2npq1, lut2npq2), and zeaxanthin (npq1, npq2). The kinetics of the two components of NPQ induction arising from zeaxanthin-independent and zeaxanthin-dependent qE were both sensitive to changes in the protein composition of the photosystem II antenna. The replacement of lutein by zeaxanthin or violaxanthin in the internal Lhcb protein-binding sites affected the kinetics and relative amplitude of each component as well as the absolute chlorophyll fluorescence lifetime. Both components of qE were characterized by a conformational change leading to nearly identical absorption changes in the Soret region that indicated the involvement of the LHCII lutein 1 domain. Based on these observations, we suggest that both components of qE arise from a common quenching mechanism based upon a conformational change within the photosystem II antenna, optimized by Lhcb subunit-subunit interactions and tuned by the synergistic effects of external and internally bound xanthophylls.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Alexander V. Ruban (a.ruban{at}qmul.ac.uk).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.129957

^* Corresponding author; e-mail a.ruban{at}qmul.ac.uk.

Received September 16, 2008; accepted November 11, 2008; published November 14, 2008.

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