0 1993 American Society for Photobiology MULTIFREQUENCY CROSS-CORRELATION PHASE FLUOROMETRY OF CHLOROPHYLL a FLUORESCENCE IN THYLAKOID AND

Abstract- We prescnt here a comparative study on the decay of chlorophyll (Chl) u fluorescence yield in thylakoid membranes and photosystem 11 (PSI1)-enriched samples, measured with multifrequency cross-correlation phase fluorometry. These measurements confirm the general conclusions of Van Mieghem ef al. (Binchim. Biophys. Acta 1100, 198-206, 1992), obtained with a flash method, on the effects of reduction of the primary quinone acceptor (QA) on Chi a fluorescence yield of PSI. Different states of the reaction centers of PSII were produced by: ( 1) pretreatment with sodium dithionite and mcthyl viologen followed by laser illumination: the doubly reduced QA (Q4HZ) centers: ( 2) with laser illumination or pretreatment with diuron: QA- centers; and (3) the addition ofmicromolar concentration of dichlorobenzoquinonc (DCBQ): oxidized QA centers. The data were analyzed with Lorentzian distribution as well as with multiexponential fluorescence decay functions. The analysis with Lorcntzian distribution function showed that upon formation of QA. the major lifetime distribution peak shifted to longer lifetimes: from 0.25 ns to 1.66 ns (pea thylakoid membrancs) and from 0.24 ns to 1.31 ns (core PSII). However, when QAHZ was formed, the lifetime distribution peaks shifted back to shorter lifetimes (0.574.77 ns) both in thylakoids and PSIl membranes. Multiexponential analysis showed three lifetime components: fast (40-400 ps), middle (300-1 500 ps) and slow (5-25 ns). When QA was formed in PSI1 centers, the amplitude of the fast Component decreased, but both thc amplitude and the lifetime of the middle component increased severalfold. However, when Q,, was doubl