The degree of functional separation between the two photosystems in isolated thylakoid membranes deduced from inhibition studies of the imbalance in photoactivities (original) (raw)
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Quantification of photosystem I and II in different parts of the thylakoid membrane from spinach
Biochimica Et Biophysica Acta-bioenergetics, 2004
Electron paramagnetic resonance (EPR) was used to quantify Photosystem I (PSI) and PSII in vesicles originating from a series of welldefined but different domains of the thylakoid membrane in spinach prepared by non-detergent techniques. Thylakoids from spinach were fragmented by sonication and separated by aqueous polymer two-phase partitioning into vesicles originating from grana and stroma lamellae. The grana vesicles were further sonicated and separated into two vesicle preparations originating from the grana margins and the appressed domains of grana (the grana core), respectively. PSI and PSII were determined in the same samples from the maximal size of the EPR signal from P700 + and Y D S , respectively. The following PSI/PSII ratios were found: thylakoids, 1.13; grana vesicles, 0.43; grana core, 0.25; grana margins, 1.28; stroma lamellae 3.10. In a sub-fraction of the stroma lamellae, denoted Y-100, PSI was highly enriched and the PSI/PSII ratio was 13. The antenna size of the respective photosystems was calculated from the experimental data and the assumption that a PSII center in the stroma lamellae (PSIIh) has an antenna size of 100 Chl. This gave the following results: PSI in grana margins (PSIa) 300, PSI (PSIh) in stroma lamellae 214, PSII in grana core (PSIIa) 280. The results suggest that PSI in grana margins have two additional light-harvesting complex II (LHCII) trimers per reaction center compared to PSI in stroma lamellae, and that PSII in grana has four LHCII trimers per monomer compared to PSII in stroma lamellae. Calculation of the total chlorophyll associated with PSI and PSII, respectively, suggests that more chlorophyll (about 10%) is associated with PSI than with PSII. D
Biochemistry, 2007
A mild sonication and phase fractionation method has been used to isolate five regions of the thylakoid membrane in order to characterize the functional lateral heterogeneity of photosynthetic reaction centers and light harvesting complexes. Low-temperature fluorescence and absorbance spectra, absorbance cross-section measurements, and picosecond time-resolved fluorescence decay kinetics were used to determine the relative amounts of photosystem II (PSII) and photosystem I (PSI), to determine the relative PSII antenna size, and to characterize the excited-state dynamics of PSI and PSII in each fraction. Marked progressive increases in the proportion of PSI complexes were observed in the following sequence: grana core (BS), whole grana (B3), margins (MA), stroma lamellae (T3), and purified stromal fraction (Y100). PSII antenna size was drastically reduced in the margins of the grana stack and stroma lamellae fractions as compared to the grana. Picosecond time-resolved fluorescence decay kinetics of PSII were characterized by three exponential decay components in the grana fractions, and were found to have only two decay components with slower lifetimes in the stroma. Results are discussed in the framework of existing models of chloroplast thylakoid membrane lateral heterogeneity and the PSII repair cycle. Kinetic modeling of the PSII fluorescence decay kinetics revealed that PSII populations in the stroma and grana margin fractions possess much slower primary charge separation rates and decreased photosynthetic efficiency when compared to PSII populations in the grana stack. 905 688-1855. Phone: 905 688-5550 ext 3826. ‡ Brock University. § Uppsala University. 1 Abbreviations: PS, photosystem; RC, reaction center; Chl, chlorophyll; P680, primary electron donor in photosystem II; Q A , primary quinone electron acceptor in photosystem II; DAS, decay-associated spectrum; F 0, the minimal fluorescence level associated with photochemically active or "open" reaction centers with an oxidized primary quinone electron acceptor, QA; FM, the maximal level of fluorescence associated with photochemically inactive or "closed" reaction centers with reduced primary quinone electron acceptor, Q A .
Proceedings of the National Academy of Sciences of the United States of America, 1995
Under conditions (0.2% CO_2; 1% O_2) that allow high rates of photosynthesis, chlorophyll fluorescence was measured simultaneously with carbon assimilation at various light intensities in spinach (Spinacia oleracea) leaves. Using a stoichiometry of 3 ATP/CO_2 and the known relationship between ATP synthesis rate and driving force (Delta pH), we calculated the light-dependent pH gradient (Delta pH) across the thylakoid membrane in intact leaves. These Delta pH values were correlated with the photochemical (q_P) and nonphotochemical (q_N) quenching of chlorophyll fluorescence and with the quantum yield of photosystem II (PhiPSII). At Delta pH > 2.1 all three parameters (q_P, q_N, and PhiPSII) changed very steeply with increasing Delta pH (decreasing pH in the thylakoid). The observed pH dependences followed hexacooperative titration curves with slightly different pK_a values. The significance of the steep pH dependences with slightly different pK_a values is discussed in relation to the regulation of photosynthetic electron transport in intact leaves.
Archives of Biochemistry and Biophysics, 1984
Uncoupled noncyclic electron flow in stacked (granal) chloroplasts with a lateral heterogeneity in the distribution of the two photosystems has been compared with that in unstacked (agranal) chloroplasts with a near-uniform distribution. Chloroplasts were maintained in either structural state in the same assay medium so as to equalize effects of ionic composition which may influence reaction rates. The assay medium, an ion-deficient solution, was capable of supporting high rates of electron flow from water to methyl viologen. At high irradiance, unstacked chloroplasts exhibited an uncoupled rate which was 30% (in chloroplasts isolated from lettuce grown in low light) or 55% (in chloroplasts isolated from lettuce grown in high light) higher than that of stacked chloroplasts; the percentage remained relatively constant in the temperature range 7 to 22°C for both highlight and low-light chloroplasts. At low irradiance, stacked lowlight chloroplasts, despite the spatial separation of the two photosystems, gave higher rates of electron flow than did unstacked low-light chloroplasts. The addition of MgClz to stacked chloroplasts increased the uncoupled rate of noncyclic electron flow, but only at relatively high irradiances. The differences observed for stacked and unstacked chloroplasts, and for highlight and low-light chloroplasts are discussed. The approach taken in this work should be useful in other comparisons of stacked and unstacked chloroplasts. An outstanding structural feature of increasingly pointed to an extremely hetchloroplasts of most higher plants and erogeneous distribution of the two phosome green algae is the formation of granal tosystems. PS I centers are largely exstacks consisting of a number of appressed cluded from the appressed membrane rethylakoids connected by nonappressed gions where PS II centers are present (12), membranes (l-8). Since the early discovery and recent work seems to indicate the exthat granal membranes are enriched in clusion of PS II centers from nonappressed Photosystem (PS)' II, and nonappressed membranes (13). A mechanism through membranes are enriched in PS I centers which such a heterogeneous distribution (g-11), recent experimental evidence has may occur has been proposed (14).
Segregation of the photosystems in thylakoids depends on their size
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2003
Lateral segregation of two types of photosystems in thylakoid membranes of green plants is one of the key factors that provide the stability and fine-tuning of the light quanta supply by pigment proteins and non-cyclic electron transport. Due to this specific feature of the membrane structural organization, the photosynthetic units function in the green plants with optimal performance. In this report a mesoscopic theory is outlined to address the physical aspects of segregation phenomenon. Results of theoretical studies and computer simulations suggest that charge mismatch and the size difference between two photosystems in grana are most responsible for their lateral segregation, which is driven by the screened electrostatic and lipid-induced interactions. Comparative simulations of photosystems of different sizes show the crucial dependence of their ordering on a geometrical parameter. It seems that the size effect alone may prevent photosystems from segregated arrangement in cyanobacterial thylakoids.
Photochem. Photobiol. Sci., 2008
Heat-induced changes in photosystem I (PSI) have been studied in terms of rates of oxygen consumption using various donors (DCPIPH 2 , TMPD red and DAD red ), formation of photo-oxidized P700 and changes in Chl a fluorescence emission at 77 K. Linear heating of thylakoid membranes from 35 • C to 70 • C caused an enhancement in PSI-mediated electron transfer rates (DCPIPH 2 →MV) up to 55 • C. However, no change was observed in PSI rates when other electron donors were used (TMPD red and DAD red ). Similarly, Chl a fluorescence emission spectra at 77 K of heat-treated thylakoid membranes did not show any increase in peak at 735 nm, however, a significant decrease was observed as a function of temperature in the peaks at 685 and 694 nm. In DCMU-treated control thylakoid membranes maximum photo-oxidized P700 was generated at g = 2.0025. In heat-treated thylakoid membranes maximum intensity of photo-oxidized P700 signal was observed at ∼50-55 • C without DCMU treatment. The steady-state signal of the photo-oxidized P700 was studied in the presence of DCPIPH 2 and TMPD red as electron donors in DCMU-treated control and in 50 • C treated thylakoid membranes. We present here the first of such comparative study of PSI activity in terms of the rates of oxygen consumption and re-reduction kinetics of photo-oxidized P700 in the presence of different electron donors. It appears that the formation of the P700 + signal in heat-treated thylakoid membranes is due to an inhibited electron supply from PSII and not due to spillover or antenna migration.
FEBS Letters, 1994
Proton and electron transfer at the reducing side of photosystem II of green plants was studied under flashing light, the former at improved time resolution by using Neutral red. The rates of electron transfer within QAFeQB were determined by pump-probe flashes through electrochromic transients. The extent of proton binding was about 1 H+/e-. The rates of proton transfer were proportional to the concentration of Neutral red (collisional transfer), whereas the rates of electron transfer out of QA- and from QAFeQB- to the cytochrome b6f complex were constant. The half-rise times of electron transfer (tau e) and the apparent times of proton binding (tau h) at 30 microM Neutral red were: QA- --> FeIIIQB (tau c < or = 100 microseconds, tau h = 230 microseconds); QA- --> FeIIQB (tau c = 150 microseconds, tau h = 760 microseconds); and QA- --> FeIIQB (tau c = 150 microseconds, tau h = 760 microseconds); and QA- --> FeIIQB (tau c = 620 microseconds, tau h = 310 microseconds).
Biologia Plantarum, 2011
The effects of temperature (25-45 °C) and pH (7.5-5.5) on photosystem (PS) 2 was studied in spinach (Spinacia oleracea L.) thylakoid membranes using chlorophyll a fluorescence induction kinetics. In high temperature and low pH treated thylakoid membranes a decline in the variable to maximum fluorescence ratio (F v /F m) and PS 2 electron transport rate were observed. More stacking in thylakoid membranes, studied by digitonin fractionation method, was observed at low pH, while the degree of unstacking increased under high temperature conditions. We conclude that the change in pH does not significantly affect the donor/acceptor side of PS 2 while high temperature does. Fluorescence emission spectra at 77 K indicated that low pH is associated with energy redistribution between the two photosystems while high temperature induced changes do not involve energy redistribution. We suggest that both, high temperature and low pH, show an inhibitory effect on PS 2 but their mechanisms of action are different.