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Title: Effect Of Calcium Chelators on the Formation and Oxidation of the Slowly Relaxing Reduced Plastoquinone Pool in Calcium-Depleted PSII Membranes. Investigation of the F0 Yield

Abstract

The F{sub 0} fluorescence yield in intact photosystem II (PSII), Ca-depleted PSII (PSII(-Ca/NaCl)), and Mn-depleted PSII membranes was measured before and after dim light treatment (1-2 min), using flash-probe fluorescence and fluorescence induction kinetic measurements. The value of F{sub 0} after the light treatment (F{sup '}{sub 0}) was larger than F{sub 0} in dark-adapted PSII membranes and depended on the appearance of the slowly relaxing, reduced plastoquinone pool (t{sub 1/2} = 4 min) formed during preillumination, which was not totally reoxidized before the F{sup '}{sub 0} measurement. In PSII(-Ca/NaCl) such a pool also appeared, but the F{sup '}{sub 0} yield was even higher than in intact PSII membranes. In Mn-depleted PSII membranes, the pool did not form. Interestingly, the yield of F{sup '}{sub 0} in Ca-depleted PSII membranes prepared using chelators (EGTA and citrate) or containing 5 mM EGTA was significantly lower than in PSII(-Ca/NaCl) samples prepared without chelators. These data indicate that chelators inhibit the reduction of QA and QB and formation of the slowly relaxing plastoquinone pool, or alternatively they increase the rate of its oxidation. Such an effect can be explained by coordination of the chelator molecule to the Mn cluster in PSII(-Ca/NaCl) membranes, rather than differentmore » amounts of residual Ca{sup 2+} in the membranes (with or without the chelator), since the remaining oxygen-evolving activity ({approx}15%) in PSII(-Ca/NaCl) samples did not depend on the presence of the chelator. Thus, chelators of calcium cations not only have an effect on the EPR properties of the S2 state in PSII(-Ca/NaCl) samples, but can also influence the PSII properties determining the rate of plastoquinone pool reduction and/or oxidation. The effect of some toxic metal cations (Cd, Cu, Hg) on the formation of the slowly relaxing pool in PSII membranes was also studied.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
982267
DOE Contract Number:
AC36-08GO28308
Resource Type:
Journal Article
Resource Relation:
Journal Name: Biochemistry (Moscow); Journal Volume: 72; Journal Issue: 11, 2007
Country of Publication:
United States
Language:
English
Subject:
09 BIOMASS FUELS; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 59 BASIC BIOLOGICAL SCIENCES; CALCIUM; CATIONS; DATA; EGTA; ELECTRON SPIN RESONANCE; FLUORESCENCE; INDUCTION; KINETICS; MEMBRANES; METALS; METHYL METHANESULFONATE; MOLECULES; OXIDATION; PLASTOQUINONE; PONDS; REDUCTION; VISIBLE RADIATION; YIELDS; Energy Sciences; Photoconversion

Citation Formats

Semin, B. K., Davletshina, L. N., Bulychev, A. A., Ivanov, I. I., Seibert, M., and Rubin, A. B. Effect Of Calcium Chelators on the Formation and Oxidation of the Slowly Relaxing Reduced Plastoquinone Pool in Calcium-Depleted PSII Membranes. Investigation of the F0 Yield. United States: N. p., 2007. Web. doi:10.1134/S0006297907110065.
Semin, B. K., Davletshina, L. N., Bulychev, A. A., Ivanov, I. I., Seibert, M., & Rubin, A. B. Effect Of Calcium Chelators on the Formation and Oxidation of the Slowly Relaxing Reduced Plastoquinone Pool in Calcium-Depleted PSII Membranes. Investigation of the F0 Yield. United States. doi:10.1134/S0006297907110065.
Semin, B. K., Davletshina, L. N., Bulychev, A. A., Ivanov, I. I., Seibert, M., and Rubin, A. B. Mon . "Effect Of Calcium Chelators on the Formation and Oxidation of the Slowly Relaxing Reduced Plastoquinone Pool in Calcium-Depleted PSII Membranes. Investigation of the F0 Yield". United States. doi:10.1134/S0006297907110065.
@article{osti_982267,
title = {Effect Of Calcium Chelators on the Formation and Oxidation of the Slowly Relaxing Reduced Plastoquinone Pool in Calcium-Depleted PSII Membranes. Investigation of the F0 Yield},
author = {Semin, B. K. and Davletshina, L. N. and Bulychev, A. A. and Ivanov, I. I. and Seibert, M. and Rubin, A. B.},
abstractNote = {The F{sub 0} fluorescence yield in intact photosystem II (PSII), Ca-depleted PSII (PSII(-Ca/NaCl)), and Mn-depleted PSII membranes was measured before and after dim light treatment (1-2 min), using flash-probe fluorescence and fluorescence induction kinetic measurements. The value of F{sub 0} after the light treatment (F{sup '}{sub 0}) was larger than F{sub 0} in dark-adapted PSII membranes and depended on the appearance of the slowly relaxing, reduced plastoquinone pool (t{sub 1/2} = 4 min) formed during preillumination, which was not totally reoxidized before the F{sup '}{sub 0} measurement. In PSII(-Ca/NaCl) such a pool also appeared, but the F{sup '}{sub 0} yield was even higher than in intact PSII membranes. In Mn-depleted PSII membranes, the pool did not form. Interestingly, the yield of F{sup '}{sub 0} in Ca-depleted PSII membranes prepared using chelators (EGTA and citrate) or containing 5 mM EGTA was significantly lower than in PSII(-Ca/NaCl) samples prepared without chelators. These data indicate that chelators inhibit the reduction of QA and QB and formation of the slowly relaxing plastoquinone pool, or alternatively they increase the rate of its oxidation. Such an effect can be explained by coordination of the chelator molecule to the Mn cluster in PSII(-Ca/NaCl) membranes, rather than different amounts of residual Ca{sup 2+} in the membranes (with or without the chelator), since the remaining oxygen-evolving activity ({approx}15%) in PSII(-Ca/NaCl) samples did not depend on the presence of the chelator. Thus, chelators of calcium cations not only have an effect on the EPR properties of the S2 state in PSII(-Ca/NaCl) samples, but can also influence the PSII properties determining the rate of plastoquinone pool reduction and/or oxidation. The effect of some toxic metal cations (Cd, Cu, Hg) on the formation of the slowly relaxing pool in PSII membranes was also studied.},
doi = {10.1134/S0006297907110065},
journal = {Biochemistry (Moscow)},
number = 11, 2007,
volume = 72,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Extraction of Ca{sup 2+} from the O{sub 2}-evolving complex (OEC) of photosystem II (PSII) membranes with 2 M NaCl in the light (PSII(-Ca/NaCl)) results in 90% inhibition of the O{sub 2}-evolution reaction. However, electron transfer from the donor to acceptor side of PSII, measured as the reduction of the exogenous acceptor 2,6-dichlorophenolindophenol (DCIP) under continuous light, is inhibited by only 30%. Thus, calcium extraction from the OEC inhibits the synthesis of molecular O{sub 2} but not the oxidation of a substrate we term X, the source of electrons for DCIP reduction. The presence of electron transfer across PSII(-Ca/NaCl) membranes wasmore » demonstrated using fluorescence induction kinetics, a method that does not require an artificial acceptor. The calcium chelator, EGTA (5 mM), when added to PSII(-Ca/NaCl) membranes, does not affect the inhibition of O{sub 2} evolution by NaCl but does inhibit DCIP reduction up to 92% (the reason why electron transport in Ca{sup 2+}-depleted materials has not been noticed before). Another chelator, sodium citrate (citrate/low pH method of calcium extraction), also inhibits both O{sub 2} evolution and DCIP reduction. The role of all buffer components (including bicarbonate and sucrose) as possible sources of electrons for PSII(-Ca/NaCl) membranes was investigated, but only the absence of chloride anions strongly inhibited the rate of DCIP reduction. Substitution of other anions for chloride indicates that Cl{sup -} serves its well-known role as an OEC cofactor, but it is not substrate X. Multiple turnover flash experiments have shown a period of four oscillations of the fluorescence yield (both the maximum level, F{sub max}, and the fluorescence level measured 50 s after an actinic flash in the presence of DCMU) in native PSII membranes, reflecting the normal function of the OEC, but the absence of oscillations in PSII(-Ca/NaCl) samples. Thus, PSII(-Ca/NaCl) samples do not evolve O{sub 2} but do transfer electrons from the donor to acceptor sides and exhibit a disrupted S-state cycle. We explain these results as follows. In Ca{sup 2+}-depleted PSII membranes, obtained without chelators, the oxidation of the OEC stops after the absorption of three quanta of light (from the S1 state), which should convert the native OEC to the S4 state. An one-electron oxidation of the water molecule bound to the Mn cluster then occurs (the second substrate water molecule is absent due to the absence of calcium), and the OEC returns to the S3 state. The appearance of a sub-cycle within the S-state cycle between S3-like and S4-like states supplies electrons (substrate X is postulated to be OH{sup -}), explains the absence of O{sub 2} production, and results in the absence of a period of four oscillation of the normal functional parameters, such as the fluorescence yield or the EPR signal from S2. Chloride anions probably keep the redox potential of the Mn cluster low enough for its oxidation by Y{sub Z}{sup {lg_bullet}}.« less
  • The eukaryotic green alga Dunaliella tertiolecta acclimates to decreased growth irradiance by increasing cellular levels of light-harvesting chlorophyll protein complex apoproteins associated with photosystem II (LHCIIs), whereas increased growth irradiance elicits the opposite response. Nuclear run-on transcription assays and measurements of cab mRNA stability established that light intensity-dependent changes in LHCII are controlled at the level of transcription. cab gene transcription in high-intensity light was partially enhanced by reducing plastoquinone with 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU), whereas it was repressed in low-intensity light by partially inhibiting the oxidation of plastoquinol with 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB). Uncouplers of photosynthetic electron transport and inhibition of watermore » splitting had no effect on LHCII levels. These results strongly implicate the redox state of the plastoquinone pool in the chloroplast as a photon-sensing system that is coupled to the light-intensity regulation of nuclear-encoded cab gene transcription. The accumulation of cellular chlorophyll at low-intensity light can be blocked by cytoplasmically directed phosphatase inhibitors, such as okadaic acid, microcystin L-R, and tautomycin. Gel mobility-shift assays revealed that cells grown in high-intensity light contained proteins that bind to the promoter region of a cab gene carrying sequences homologous to higher plant light-responsive elements. On the basis of these experimental results, we propose a model for a light intensity signaling system where cab gene expression is reversibly repressed by a phosphorylated factor coupled to the redox status of plastoquinone through a chloroplast protein kinase. 54 refs., 5 figs.« less
  • The utility of a recycled flow system for the efficient quantitative analysis of NMR spectra is demonstrated. Requisite conditions are first established for the quantitative flow experiment and then applied to a variety of compounds. An application of the technique to determination of the average polymer chain length for a silicone polymer by quantitative flow /sup 29/Si NMR is also presented. 10 references, 4 figures, 3 tables.
  • A recycled flow Fourier transform nuclear magnetic resonance system is evaluated for analytical utility. It is demonstrated to have wide applicability, particularly for the observation of nuclei with long relaxation times or negative nuclear Overhauser effects. Signal to noise improvements of a factor of 2-10 are demonstrated for /sup 13/C, /sup 31/P, /sup 113/Cd, /sup 29/Si, and /sup 15/N NMR spectra of model compounds. The approach is shown to be compatible with the use of immobilized free radicals which reduce required premagnetization volumes and with spectral editing techniques (e.g., distortionless enhancement by polarization transfer (DEPT)). 19 references, 8 figures, 4more » tables.« less