In diatoms, a transthylakoid proton gradient alone is not sufficient to induce a non-photochemical fluorescence quenching

Non-photochemical fluorescence quenching (NPQ) in diatoms is associated with a xanthophyll cycle involving diadinoxanthin (DD) and its de-epoxidized form, diatoxanthin (DT). In higher plants, an obligatory role of de-epoxidized xanthophylls in NPQ remains controversial and the presence of a transthylakoid proton gradient (ApH) alone may induce NPQ. We used inhibitors to alter the amplitude of ApH and/or DD de-epoxidation, and coupled NPQ. No DeltapH-dependent quenching was detected in the absence of DT. In diatoms, both ApH and DT are required for NPQ. The binding of DT to protonated antenna sites could be obligatory for energy dissipation. (C) 2002 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.