Dark-induced reduction of the plastoquinone pool in zooxanthellae of scleractinian corals and implications for measurements of chlorophyll a fluorescence

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Journal Article
Symbiosis, 2008, 46 (1), pp. 45 - 56
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Fluorometric measurements of maximum quantum yield (Fv/F m) and fast induction curves (FICs) require coral samples to be dark-adapted (DA). Pathways causing dark-reduction of the plastoquinone (PQ) pool are shown here to be active in corals. Early morning sunlight and far-red light successfully increased Fv/Fm and lowered the O and J steps of FICs in corals that were darkened overnight. The thick-tissued massive coral, Cyphastrea serailia, was shown to be more prone to reduction of the PQ pool, with significant reductions in Fv/Fm occurring after 10 min of DA, and elevated J steps occurring within 200 s following a far-red flash. In thinner-tissued branching species, Pocillopora damicornis and Acropora nobilis, elevation of the J step also occurred within 200 s of DA, but a drop in Fv/Fm was only manifested after 30 min. Pre-exposure to far-red light is an effective and simple procedure to ensure determination of the true maximum quantum yield of Photosystem II (PSII) and accurate FICs which require a fully oxidised inter-system electron transport chain and open PSII reaction centres. ©2008 Balaban.
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