NONPHOTOCHEMICAL QUENCHING OF CHLOROPHYLL FLUORESCENCE IN PHOTOSYNTHESIS - 5-HYDROXY-1,4-NAPHTHOQUINONE IN SPINACH THYLAKOIDS AS A MODEL FOR ANTENNA BASED QUENCHING MECHANISMS

In vivo mechanisms of non-photochemical quenching that contribute to e nergy dissipation in higher plants are still a source of some controve rsy. In the present study we used an exogenous oxidized quinone, 5-hyd roxy-1,4-naphthoquinone to induce quenching of chlorophyll excited sta tes in photosynthetic light-harvesting antenna and to elucidate the me chanism of non-photochemical quenching of chlorophyll fluorescence by this quinone. Excitation dynamics in isolated spinach thylakoids in th e presence of an exogenous fluorescence quencher was studied by a comb ined analysis of data gathered from independent techniques (fluorescen ce yields, effective absorption cross-sections and picosecond kinetics ). The application of a kinetic model for photosystem II to a combined data set of fluorescence decay kinetics and absorbance cross-section measurements was used to quantify antenna quenching by a model antenna quencher, 5-hydroxy-1,4-naphthoquinone. We observed depressions in F- 0 and photosystem II absorption cross-sections, paralleled with an inc rease of the rate constant for excitation decay in antenna. This appro ach is a first step towards quantifying the amount of antenna quenchin g contributing to non-photochemical quenching in vivo, evaluation of t he contributions of antenna and reaction centre mechanisms to it and l ocalization of the sites of non-photochemical energy dissipation in in tact plant systems. (C) 1998 Elsevier Science B.V.