Acclimation- and mutation-induced enhancement of PsbS levels affects the kinetics of non-photochemical quenching in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> |
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Authors: | Ahmad Zia Matthew P Johnson Alexander V Ruban |
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Institution: | (1) School of Biological and Chemical Sciences, Queen Mary University of London, Mile End, Bancroft Road, Fogg Building, London, E1 4NS, UK; |
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Abstract: | The efficiency of photosystem II antenna complexes (LHCs) in higher plants must be regulated to avoid potentially damaging
overexcitation of the reaction centre in excess light. Regulation is achieved via a feedback mechanism known as non-photochemical
quenching (NPQ), triggered the proton gradient (ΔpH) causing heat dissipation within the LHC antenna. ΔpH causes protonation
of the LHCs, the PsbS protein and triggers the enzymatic de-epoxidation of the xanthophyll, violaxanthin, to zeaxanthin. A
key step in understanding the mechanism is to decipher whether PsbS and zeaxanthin cooperate to promote NPQ. To obtain clues
about their respective functions we studied the effects of PsbS and zeaxanthin on the rates of NPQ formation and relaxation
in wild-type Arabidopsis leaves and those overexpressing PsbS (L17) or lacking zeaxanthin (npq1). Overexpression of PsbS was found to increase the rate of NPQ formation, as previously reported for zeaxanthin. However,
PsbS overexpression also increased the rate of NPQ relaxation, unlike zeaxanthin, which is known decrease the rate. The enhancement
of PsbS levels in plants lacking zeaxanthin (npq1) by either acclimation to high light or crossing with L17 plants showed that the effect of PsbS was independent of zeaxanthin.
PsbS levels also affected the kinetics of the 535 nm absorption change (ΔA535), which monitors the formation of the conformational
state of the LHC antenna associated with NPQ, in an identical way. The antagonistic action of PsbS and zeaxanthin with respect
to NPQ and ΔA535 relaxation kinetics suggests that the two molecules have distinct regulatory functions. |
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