ROLE OF DELTA-PH IN THE MECHANISM OF ZEAXANTHIN-DEPENDENT AMPLIFICATION OF Q(E)

The influence of zeaxanthin on the high-energy-state fluorescence quen ching (q(E)) and the pH dependence of the maximum chlorophyll fluoresc ence yield (F-m) was examined in spinach thylakoids. High contents of zeaxanthin were achieved using different pretreatments. A pronounced, zeaxanthin-dependent amplification of non-photochemical quenching (NPQ ) was exclusively found in thylakoids containing zeaxanthin, synthesiz ed in the dark via the buildup of an artificial Delta pH. These thylak oids also showed a significant quenching of chlorophyll fluorescence i n the range pH 5.5-6.3, where no or only slight quenching was visible in zeaxanthin-free thylakoids. Thylakoids containing high amounts of z eaxanthin from a dark pretreatment at pH 5.5 (in the absence of Delta pH) showed no pronounced amplification of NPQ and were insensitive to incubation at lower pH values. Therefore we propose that it is the Del ta pH during the synthesis of zeaxanthin that activates the mechanism of zeaxanthin-dependent amplification of q(E).