Chlorophyll a fluorescence lifetime distributions in open and closed Photosystem II reaction center preparations

Abstract

We have measured the decay of chlorophyll a fluorescence at 4 °C under anaerobic conditions in stabilized photosystem !I reaction center complex isolated from spinach, using multifrequeucy (2-400 MHz) cross-correlation phase fluorometry. Examination of our data shows that although the fluorescence decay of open reaction centers (i.e., when both the electron donor P-680 and the electron acceptor pheophytin are capable of engaging in charge separation) can he analyzed as a multiexponential decay, another representation of the data is obtained when the decay is analyzed using a continuous distribution of lifetimes. [478][479][480][481][482][483][484][485][486] for the DI-D2-cytochrome /}-559 complex, obtained for F682 at 4°C by a time-resolved photon-counting spectrofiuorometer. When the reaction centers are closed by pretreatment with sodium dithionite and methyl viologen followed by exposure to laser excitation, conditions known to result in accumulation of reduced pheophytin, a dramatic decrease in the contribution of the slow lifetime component(s) is observed. These results suggest that the slow distribution lifetime component(s) in the 5-20 ns range originate(s) in the back reaction of the charge separated state. On the other hand, the fast lifetime component(s) in the picosecond range may he only partially related to the charge separation, since no dramatic change is observed upon closure of the reaction center. Perhaps, this component is related, in part, to the excitation energy migration among the various chromophores in the reaction center preparations.

Molecular and Global Time-resolved Analysis of a psbSGene Dosage Effect on pH- and Xanthophyll Cycle-dependent Nonphotochemical Quenching in Photosystem II

“…Thylakoid membrane energization by a ⌬pH results in a distinct conversion of the W state distribution to a shorter, usually narrower lifetime, centered at ϳ1.6 -1.8 ns and referred to as the X state. The W to X shift is hypothesized to be related to protein conformational changes (15) in the molecular environment of the protein-bound fluorophores, in this case fluorescing Chls (12,13,16), caused by protonation of lumen-exposed carboxylate groups of proteins in the PSII inner antenna. The conformational changes are associated with the activation for potential structural interactions between the xanthophylls Z and A and the PSII proteins.…”

Xanthophyll cycle-dependent quenching of photosystem II chlorophyll a fluorescence: formation of a quenching complex with a short fluorescence lifetime.

“…The shift in phase angles (phase) and demodulation ratios (modulation) of the sample fluorescence emission were analyzed for fluorescence lifetime information. Further details and explanation of the multifrequency crosscorrelation technique can be found elsewhere (18)(19)(20) (Fig. 3A).…”

“…1), enhances LHCII aggregation and hence NPQ by creating weakly fluorescent long-wavelength-absorbing chlorophylls. However, Vx deepoxidation apparently does not induce longwavelength-absorbing chlorophylls in leaves (10), and there is no indication of long-wavelength chlorophylls in other chloroplast studies (11,12 (18)(19)(20). Sample excitation at 610 nm was provided by a cavity-dumped rhodamine 6G dye laser (Coherent, Palo Alto, CA) pumped by a mode-locked Nd:YAG laser (Coherent).…”

Govindjee at 80: more than 50 years of free energy for photosynthesis

“…What Govindjee loves the most is: chlorophyll a fluorescence and its relationship to photosynthesis; he was the first one to introduce measurements of lifetime of chlorophyll a fluorescence to understand photoprotection in plants Govindjee's main love in the field of photosynthesis has been to relate chlorophyll a fluorescence to photosynthesis, especially to regulation of photosynthesis. This has led to a large number of edited volumes and reviews including: Govindjee et al (1986), Govindjee (1995Govindjee ( , 2004, Strasser et al (1995), Papageorgiou and Govindjee (2004), Papageorgiou and Govindjee (2011), Govindjee (2011, 2012) and Kalaji et al (2012). Likewise this area of research has included a large number of graduate students including Carl Cederstrand (PhD, 1965), Louisa Yang (MS, 1965, Anne Krey (MS, 1966), George Papageorgiou (PhD, 1968), John C. Munday (PhD, 1968), Fred Cho (PhD, 1969, Ted Mar (PhD, 1971), Maarib Bazzaz (PhD, 1972, Prasanna Mohanty (PhD, 1972), Paul Jursinic (PhD, 1977), David VanderMeulen (PhD, 1977), Daniel Wong (PhD, 1979, and Paul Spilotro (MS, 1999).…”

“…However, Govindjee pioneered, with Henri Merkelo, use of modelocked lasers to make such measurements (Merkelo et al 1969), and then subsequently made lifetime of chlorophyll a fluorescence measurements, using the phase method, in Enrico Gratton's group (see e.g., Govindjee et al 1990). …”