PICOSECOND FLUORESCENCE STUDY OF PHOTOSYNTHETIC MUTANTS OF Chlamydomonas reinhardii: ORIGIN OF THE FLUORESCENCE DECAY KINETICS OF CHLOROPLASTS

Gulotty, Robert; Mets, Laurens; Alberte, Randall S.; Fleming, Graham R.

doi:10.1111/j.1751-1097.1985.tb03516.x

Cited by 55 publications

(46 citation statements)

References 28 publications

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“…Fluorescence decay measurements were performed by using time-correlated single photon counting as described by Gulotty et al (12) with the following modifications. Excitation pulses [8-10 psec The fluorescence decay, F(t), was described as a weighted sum of exponential decays F(t) = I-Ai exp(-t/ri), [1] with ZAi = 1.0, where Ai and Ti are the preexponential amplitudes and lifetimes, respectively, of each decay component, i.…”

Section: Methodsmentioning

confidence: 99%

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Antenna size dependence of fluorescence decay in the core antenna of photosystem I: estimates of charge separation and energy transfer rates.

Owens¹,

Webb²,

Mets³

et al. 1987

Proc. Natl. Acad. Sci. U.S.A.

119

106

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We have examined the photophysics of energy migration and trapping in photosystem I by investigating the spectral and temporal properties of the fluorescence from the core antenna chlorophylls as a function of the antenna size. Time-correlated single photon counting was used to determine the fluorescence lifetimes in the isolated P700 chlorophyll a-protein complex and in a mutant of Chlamydomonas reinhardtii that lacks the photosystem II reaction center complex. The fluorescence decay in both types of sample is dominated by a fast (1545 psec) component that is attributed to the lifetime of excitations in the photosystem I core antenna. These excitations decay primarily by an efficient photochemical quenching on P700. The measured lifetimes show a linear relationship to the core antenna size. A linear dependence of the excitation lifetime on antenna size was predicted previously in a lattice model for excitation migration and trapping in arrays of photosynthetic pigments [Pearlstein, R. M. (1982) Photochem. Photobiol. 35, 83544M]. Based on this model, our data predict a time constant for photochemical charge separation in the photosystem I reaction center of 2.8 ± 0.7 or 3.4 ± 0.7 psec, assuming monomeric or dimeric P700, respectively. The predicted average single-step transfer time for excitation transfer between core antenna pigments is 0.21 ± 0.04 psec. Under these conditions, excitation migration in photosystem I is near the diffusion limit, with each excitation making an average of 2.4 visits to the reaction center before photoconversion.The primary steps in photosynthesis are absorption of light and creation of a singlet excitation, transfer of the excitation between pigment molecules, and photochemical charge separation in the reaction center. The relative kinetics of the excitation transfer and trapping reactions determine critical aspects of the overall light-harvesting process. Excitation transfer is believed to occur by an incoherent hopping mechanism (1), with the excitation following a random walk through the antenna pigments to the reaction center (2). The mechanism of charge separation depends on the unique redox properties of the reaction center pigments in the excited state and appears to be similar in bacteria and plants.The reaction center complex of purple photosynthetic bacteria contains only six pigment molecules (3), at least four of which are directly involved in the primary photochemical reactions (4). This relative simplicity has permitted measurement of the photochemical rate constant, kp, by direct excitation of the reaction center pigments (5-7). In contrast, the photosystem I and II (PSI and PSII) reaction center complexes isolated from oxygen-evolving plants contain a relatively large number (40-110) of chlorophyll a (Chl-a) molecules (8, 9). The presence of these core antenna pigments in reaction center preparations complicates spectroscopic and kinetic measurements of the primary photochemical reactions because of substantial overlap between the absorptions ofthe reaction...

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Section: Methodsmentioning

confidence: 99%

“…Timeresolved measurements on enriched PSI preparations have established an upper limit of 10 psec for charge separation in P700 (10). In efforts to model the energy transfer dynamics in oxygen-evolving systems (11,12), the assumption has been that the charge separation rate is the same as that obtained for bacterial reaction centers (13).…”

mentioning

confidence: 99%

Antenna size dependence of fluorescence decay in the core antenna of photosystem I: estimates of charge separation and energy transfer rates.

Owens¹,

Webb²,

Mets³

et al. 1987

Proc. Natl. Acad. Sci. U.S.A.

119

106

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“…Such a contribution had been expected on the basis of earlier indirect evidence (Haehnel et al, ,1983Greenetal., 1984;Magdeetal., 1982;Gulotty et al, 1982). Gulotty et al (1985) and Yamazaki et al (1985) independently also arrived at conclusions consistent with an assignment of the fastest component to PS I both by the study of picosecond fluorescence kinetics from mutants of Chlamydomonas and on the basis of time-gated fluorescence difference spectra of Chlorella, respectively. Thus it is clear that, despite the difficulties arising from the similarity of the spectra of various Chl-protein complexes, important information on the antenna organization and energy distribution could be obtained from systematic wavelength studies of the fluorescence decays.…”

Section: Introductionmentioning

confidence: 66%

“…In a four-exponential analysis these have lifetimes of 180-300 ps and approximately 600 ps . Since a three-exponential analysis which has often been applied (Haehnel et al, , 1983Gulotty et al, 1982) generally does not contain enough parameters, the faster of these PS I1 components then seems to mix most strongly with the above-mentioned fast PS I fluorescence of approximately 80 ps lifetime Gulotty et al, 1985).…”

Section: Introductionmentioning

confidence: 99%

Fluorescence Lifetimes in Photosynthetic Systems

Holzwarth

1986

Photochem & Photobiology

120

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“…So long as the sample is reasonably mogeneous, the nature of the antenna system is irreleva At some depth Xmax, the intensity is no longer sufficient sustain the reaction. This depth is found by combining Eq and 7 (13). Table 1 reports the results of fitting AGp/mo from Eq.…”

Section: Yield and Red Dropmentioning

confidence: 99%

Alternative perspective on photosynthetic yield and enhancement

Warner¹,

Berry²

1987

Proc. Natl. Acad. Sci. U.S.A.

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In the traditional Z scheme of photosynthesis the Emerson effects of red drop (decline in yield of photosynthesis in far-red light) and enhancement (of far-red yield by supplementary short-wavelength light) are taken to be evidence for the coupling in series of two photosystems that absorb unsymmetrically in the far-red region of the spectrum. An alternative explanation for red drop and enhancement is proposed here that does not invoke the series-coupling hypothesis. It is suggested that the Emerson effects may be due to the drop in intensity of radiation from sample absorption, which causes a photochemical loss when the reaction shuts off at depth in the medium. The effects of oxygen, carbon dioxide, and temperature on the yield may also be interpreted in terms of this model.In the traditional Z scheme of photosynthesis, reduction of ferredoxin by electrons donated from water is mediated by the coupling in series of photosystems I and II (PSI and PSII, respectively). Questions concerning the series coupling model arose when Rurainski and Hoch (1) found that magnesium salts increase the rate of NADP+ reduction while simultaneously decreasing the rate of P700 turnover. Melis and Brown (2) showed that the number ratio of PSII/PSI centers varies widely in different chloroplast subfragments. Anderson and Andersson (3) showed that PSI centers are concentrated in the stromal lamellae, whereas the PSII centers are found mostly in the appressed grana. Arnon et al. (4,5) demonstrated photoreduction of ferredoxin by water in the presence of inhibitors that block electron transport through plastoquinone. They suggested that the two photosystems are not coupled in series.It was the observation by Emerson et al. (6) of the decline in yield of photosynthesis in far-red light (red drop) and the enhancement of the far-red yield by supplementary shortwavelength light that provided much of the original motivation for the series-coupling model (7). Here we propose an alternative explanation for red drop and enhancement that does not require series coupling of the photosystems. The model developed below is not incompatible with series coupling of the photosystems. It is merely a simple way to account for several yield effects, some of which are commonly taken to be evidence for series coupling.

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PICOSECOND FLUORESCENCE STUDY OF PHOTOSYNTHETIC MUTANTS OF Chlamydomonas reinhardii: ORIGIN OF THE FLUORESCENCE DECAY KINETICS OF CHLOROPLASTS

Cited by 55 publications

References 28 publications

Antenna size dependence of fluorescence decay in the core antenna of photosystem I: estimates of charge separation and energy transfer rates.

Antenna size dependence of fluorescence decay in the core antenna of photosystem I: estimates of charge separation and energy transfer rates.

Fluorescence Lifetimes in Photosynthetic Systems

Alternative perspective on photosynthetic yield and enhancement

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