The effect of high-energy-state excitation quenching on maximum and dark level chlorophyll fluorescence yield

The quenching of variable fluorescence yield (q_N) and the quenching of dark level fluorescence yield (q₀) directly atributable to high-energy-state fluorescence quenching (q_E) was studied to distinguish between energy dissipation in the antenna and light harvesting complexes (antenna quenching) and energy dissipation at the reaction centres (reaction centre quenching). A consistent relationship was obtained between q_N and q₀ in barley leaves, the green alga Dunaliella C9AA and in pea thylakoids with 2,3,5,6-tetramethyl-p-phenylene diamine (DAD) as mediator of cyclic electron flow around PS 1. This correlated well with the relationship obtained using m-dinitrobenzene (DNB), a chemical model for antenna quenching, to quench fluorescence in Dunaliella C9AA or pea thylakoids. The results also correlated reasonably well with theoretical predictions by the Butler model for antenna quenching, but did not correlate with the predictions for reaction centre quenching. It is postulated that q_E quenching therefore occures in the antenna and light harvesting complexes, and that the small deviation from the Butler prediction is due to PS 2 heterogeneity.Abbreviations 9-aa 9-aminoacridine - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - EDTA Ethylenediaminetetra-acetic acid - Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulphonic acid - Mes 2-(N-morpholino) prophanesulfonate - PS 1 photosystem 1 - PS 2 photosystem 2 - Q_A and Q_B primary and secondary stable electron acceptors of photosystem 2 - q_N non-photochemical fluorescence quenching coefficient - q_E high-energy-state fluorescence quenching coefficient - q₀ quenching coefficient for F₀ - F₀ dark level fluorescence yield - F_m maximum fluorescence yield - F_v variable fluorescence yield - F_v/F_m ratio of variable to total fluorescence yield - DAD 2,3,5,6-tetramethyl-p-phenylene diamine - DNB m-dinitrobenzene