Further Studies on Quantifying Photosystem II in vivo by Flash-Induced Oxygen Yield From Leaf Discs

1991 ◽  
Vol 18 (4) ◽  
pp. 397 ◽  
Author(s):  
WS Chow ◽  
AB Hope ◽  
JM Anderson
Keyword(s):  
Steady State ◽  
Photosystem Ii ◽  
Red Light ◽  
Light Activation ◽  
Ps Ii ◽  
Dark Incubation ◽  
Leaf Discs ◽  
Reaction Centres ◽  
Oxygen Yield

It was shown briefly [W. S. Chow, A. B. Hope and J. M. Anderson (1989), Biochirnica et Biophysics Acta, 973, 105-8] that the oxygen evolved per flash from leaf discs, under steady-state flashing conditions and in the presence of background far-red light, gave a valid measure of the number of functional photosystem II (PS II) reaction centres. Further work on this direct and convenient method has been done to optimise conditions for making reliable measurements. It is found that, to obtain the higher estimates of [PS II], corresponding to functionality of practically all PS II reaction centres that bind herbicides, a form of 'light activation' is necessary after a prolonged dark pre-incubation. Without a sufficient number of flashes being given following a long dark incubation, the number of functional PS II reaction centres was underestimated. Provided light activation had occurred, the measured number of functional PS II reaction centres was independent of flash frequencies up to at least 40 Hz. The results strongly suggest that, in steady-state, light-limited photosynthesis, there does not exist any sub- stantial fraction of non-functional or 'slow' PS II reaction centres.

Is the in vivo Photosystem I Function Resistant to Photoinhibition? An Answer from Photoacoustic and Far-Red Absorbance Measurements in Intact Leaves

1991 ◽  
Vol 46 (11-12) ◽  
pp. 1038-1044 ◽  
Author(s):  
Michel Havaux ◽  
Murielle Eyletters
Keyword(s):  
Light Stress ◽  
Red Light ◽  
Light Treatment ◽  
High Light ◽  
Saturation Curve ◽  
Strong Light ◽  
Ps Ii ◽  
Fluorescence Measurements ◽  
Ps I

Abstract Preillumination of intact pea leaves with a strong blue-green light of 400 W m-2 markedly inhibited both photoacoustically monitored O2-evolution activity and PS II photochemistry as estimated from chlorophyll fluorescence measurements. The aim of the present work was to examine, with the help of the photoacoustic technique, whether this high-light treatment deteriorated the in vivo PS I function too. High-frequency photoacoustic measurements indicated that photochemical conversion of far-red light energy in PS I was preserved (and even transiently stimulated) whereas photochemical energy storage monitored in light exciting both PS I and PS II was markedly diminished. Low-frequency photoacoustic measurements of the Emerson enhancement showed a spectacular change in the PS II/PS I activity balance in favor of PS I. It was also observed that the linear portion of the saturation curve of the far-red light effect in the Emerson enhancement was not changed by the light treatment. Those results lead to the conclusion that, in contrast to PS II, the in vivo PS I photofunctioning was resistant to strong light stress, thus confirming previous suggestions derived from in vitro studies. Estimation of the redox state of the PS I reaction center by leaf absorbance measurements at ca. 820 nm suggested that, under steady illumination, a considerably larger fraction of PS I centers were in the closed state in high-light pretreated leaves as compared to control leaves, presumably allowing passive adjustment of the macroscopic quantum yield of PS I photochemis­ try to the strongly reduced photochemical efficiency of photoinhibited PS II.

Metabolie Reduction of Phenylpropanoid Compounds in Primary Leaves of Rye (Secale cereale L.) Leads to Increased UV-B Sensitivity of Photosynthesis

1993 ◽  
Vol 48 (9-10) ◽  
pp. 749-756 ◽  
Author(s):  
S. Reuber ◽  
J. Leitsch ◽  
G. H. Krause ◽  
G. Weissenböck
Keyword(s):  
Photosystem Ii ◽  
Essential Role ◽  
Phenylalanine Ammonia Lyase ◽  
Ps Ii ◽  
Efficient Inhibitor ◽  
Flavone Glycosides ◽  
Fluorescence Parameter ◽  
Secale Cereale L

Abstract In the epidermal layers of rye primary leaves two flavone glycosides and several hydroxycinnamoyl esters are localized, whereas the mesophyll contains two flavone glucuronides and two anthocyanins. The concentrations of all these potential UV-B protective phenylpropanoid compounds could be reduced by application of 2-aminoindan-2-phosphonic acid (AIP), an efficient inhibitor of phenylalanine ammonia-lyase (EC 4.1.3.5). Photosystem II in the primary leaves of seven-days-old plants, grown in the presence of 20 μm AIP up to an age of 80 h, was more severely affected by UV-B than in control plants with the normal concentration of phenylpropanoid compounds. Damage of photosystem II in vivo was estimated by measuring the chlorophyll a fluorescence (parameter FJFm) of PS II. The results indicate an essential role of phenylpropanoid com pounds as UV-B protectants in rye primary leaves

Bicarbonate-Reversible Inhibition of Plastoquinone Reductase in Photosystem II

1993 ◽  
Vol 48 (3-4) ◽  
pp. 251-258 ◽  
Author(s):  
Keyword(s):  
Photosystem Ii ◽  
Active Species ◽  
Current Status ◽  
Ps Ii ◽  
Herbicide Resistant ◽  
Purple Photosynthetic Bacteria ◽  
Slowing Down ◽  
Bicarbonate Effect ◽  
Type Data

Abstract In this paper the current status of the so-called bicarbonate effect is presented. Several chemicals (such as formate, azide, nitrite and nitric oxide) are known to inhibit the two-electron gate of photosystem II (PS II). A remerkable slowing down of QA- reoxidation and an increase in equilibrium [QA- ] have been observed after the second or the subsequent, but not the first, flash when thylakoid membranes are treated with formate, etc. And, significantly, these effects are totally and uniquely reversed upon bicarbonate addition. The current hypothesis is that bicarbonate functions as a proton shuttle that stabilizes the binding niche of QB- and stimulates platoquinol formation. This bicarbonate effect must involve both the D 1 and D 2 proteins since various herbicide-resistant D 1 mutants (e.g., D 1 -S264A , D 1 -L275F), as well as some D 2 mutants (e.g., D 2 -R251S, D 2 -R 233Q) have been found to be differentially sensitive to formate. The D 2-arginine (233, 251) effects are specific since D 2 -R 139H mutant and an­ other mutant in which an extra arginine was inserted, between F 223 and E 224 , behaves like the wild type. Data in the literature suggest that the bicarbonate binding must also involve Fe in the PS II QA-Fe -QB complex. In contrast, the QA-Fe -QB complex and the two-electron gate of both green and purple photosynthetic bacteria, including the M -E 234 G , Q and V mutants, are insensitive to bicarbonate-reversible inhibitors. We will also address the question of the nature of the active species involved and the possible role of bicarbonate in vivo.

Kinetic response of photosystem II photochemistry in the cyanobacterium Spirulina platensis to high salinity is characterized by two distinct phases

1999 ◽  
Vol 26 (3) ◽  
pp. 283 ◽  
Author(s):  
Congming Lu ◽  
Giuseppe Torzillo ◽  
Avigad Vonshak
Keyword(s):  
Electron Transport ◽  
Quantum Yield ◽  
Photosystem Ii ◽  
Spirulina Platensis ◽  
High Salinity ◽  
Photochemical Quenching ◽  
Second Phase ◽  
Ps Ii ◽  
Reaction Centres ◽  
Two Phases

The kinetic response of photosystem II (PS II) photochemistry in Spirulina platensis(Norstedt M2 ) to high salinity (0.75 M NaCl) was found to consist of two phases. The first phase, which was independent of light, was characterized by a rapid decrease (15–50%) in the maximal efficiency of PS II photochemistry (Fv /Fm), the efficiency of excitation energy capture by open PS II reaction centres (Fv′/Fm′), photochemical quenching (qp) and the quantum yield of PS II electron transport (Φ PS II) in the first 15 min, followed by a recovery up to about 80–92% of their initial levels within the next 2 h. The second phase took place after 4 h, in which further decline in above parameters occurred. Such a decline occurred only when the cells were incubated in the light, reaching levels as low as 45–70% of their initial levels after 12 h. At the same time, non-photochemical quenching (qN) and Q B -non-reducing PS II reaction centres increased significantly in the first 15 min and then recovered to the initial level during the first phase but increased again in the light in the second phase. The changes in the probability of electron transfer beyond QA (ψo) and the yield of electron transport beyond QA (φ Eo), the absorption flux (ABS/RC) and the trapping flux (TRo /RC) per PS II reaction centre also displayed two different phases. The causes responsible for the decreased quantum yield of PS II electron transport during the two phases are discussed.

Excitation pressure regulates the activation energy for recombination events in the photosystem II reaction centres of Chlamydomonas reinhardtii

2007 ◽  
Vol 85 (6) ◽  
pp. 721-729 ◽  
Author(s):  
Tessa Pocock ◽  
P. V. Sane ◽  
S. Falk ◽  
N. P.A. Hüner
Keyword(s):  
Activation Energy ◽  
Photosystem Ii ◽  
Redox Potential ◽  
Chlamydomonas Reinhardtii ◽  
Reaction Center ◽  
Growth Conditions ◽  
High Irradiance ◽  
Reaction Centres ◽  
Excitation Pressure

Using in vivo thermoluminescence, we examined the effects of growth irradiance and growth temperature on charge recombination events in photosystem II reaction centres of the model green alga Chlamydomonas reinhardtii. We report that growth at increasing irradiance at either 29 or 15 °C resulted in comparable downward shifts in the temperature peak maxima (TM) for S2QB– charge pair recombination events, with minimal changes in S2QA– recombination events. This indicates that such growth conditions decrease the activation energy required for S2QB– charge pair recombination events with no concomitant change in the activation energy for S2QA– recombination events. This resulted in a decrease in the ΔTM between S2QA– and S2QB– recombination events, which was reversible when shifting cells from low to high irradiance and back to low irradiance at 29 °C. We interpret these results to indicate that the redox potential of QB was modulated independently of QA, which consequently narrowed the redox potential gap between QA and QB in photosystem II reaction centres. Since a decrease in the ΔTM between S2QA– and S2QB– recombination events correlated with growth at increasing excitation pressure, we conclude that acclimation to growth under high excitation pressure narrows the redox potential gap between QA and QB in photosystem II reaction centres, enhancing the probability for reaction center quenching in C. reinhardtii. We discuss the molecular basis for the modulation of the redox state of QB, and suggest that the potential for reaction center quenching complements antenna quenching via the xanthophyll cycle in the photoprotection of C. reinhardtii from excess light.

scholarly journals New Perspectives on Photosystem II Reaction Centres

2020 ◽  
Vol 73 (8) ◽  
pp. 669 ◽  
Author(s):  
Jeremy Hall ◽  
Rafael Picorel ◽  
Nicholas Cox ◽  
Robin Purchase ◽  
Elmars Krausz
Keyword(s):  
Photosystem Ii ◽  
Charge Separation ◽  
Cd Spectra ◽  
Negative Component ◽  
Ps Ii ◽  
Pheophytin A ◽  
Chl A ◽  
Special Pair ◽  
Reaction Centres ◽  
Weak Luminescence

We apply the differential optical spectroscopy techniques of circular polarisation of luminescence (CPL) and magnetic CPL (MCPL) to the study of isolated reaction centres (RCs) of photosystem II (PS II). The data and subsequent analysis provide insights into aspects of the RC chromophore site energies, exciton couplings, and heterogeneities. CPL measurements are able to identify weak luminescence associated with the unbound chlorophyll-a (Chl-a) present in the sample. The overall sign and magnitude of the CPL observed relates well to the circular dichroism (CD) of the sample. Both CD and CPL are reasonably consistent with modelling of the RC exciton structure. The MCPL observed for the free Chl-a luminescence component in the RC samples is also easily understandable, but the MCPL seen near 680nm at 1.8K is anomalous, appearing to have a narrow, strongly negative component. A negative sign is inconsistent with MCPL of (exciton coupled) Qy states of either Chl-a or pheophytin-a (Pheo-a). We propose that this anomaly may arise as a result of the luminescence from a transient excited state species created following photo-induced charge separation within the RC. A comparison of CD spectra and modelling of RC preparations having a different number of pigments suggests that the non-conservative nature of the CD spectra observed is associated with the ‘special pair’ pigments PD1 and PD2.

Protection of Photosystem II by Light in Heat-Stressed Pea Leaves

1990 ◽  
Vol 45 (11-12) ◽  
pp. 1133-1141 ◽  
Author(s):  
Michel Havaux ◽  
Reto J. Strasser
Keyword(s):  
Steady State ◽  
Reaction Centers ◽  
Thermal Dissipation ◽  
Short Exposure ◽  
Variable Fluorescence ◽  
Ps Ii ◽  
Heat Injury ◽  
Actinic Light ◽  
Main Effect

Modulated 685-nm chlorophyll fluorescence was measured under steady-state conditions in pea leaves adapted to moderate actinic light. When the measurements were performed after a short exposure to heat (42 °C) in darkness, the maximal (Fm) and steady-state (Fs) fluorescence levels were dramatically and irreversibly quenched whereas the basic fluorescence Fo remained unchanged. Concomitantly , photo synthetic O2 evolution was irreversibly inhibited. Analysis of the fluorescence data suggested that the heat treatment affected primarily the PS II reaction center, with the main effect being presumably an increased thermal dissipation of the excita­tion energy transferred to the reaction centers. In contrast, when heat stress was imposed in the presence of light, the loss of variable fluorescence (Fm-Fo) was much less marked and was fully reversible. In addition , no inhibition of in vivo O2 : evolution was observed when the samples heated in the light were recooled at 25 °C. The results indicate that light acted as an efficient protector of PS II against heat injury.

scholarly journals Allosteric regulation of the light-harvesting system of photosystem II

2000 ◽  
Vol 355 (1402) ◽  
pp. 1361-1370 ◽  
Author(s):  
Peter Horton ◽  
Alexander V. Ruban ◽  
Mark Wentworth
Keyword(s):  
Photosystem Ii ◽  
Xanthophyll Cycle ◽  
Light Harvesting ◽  
Allosteric Regulation ◽  
Photochemical Quenching ◽  
Protein Subunit ◽  
Ps Ii ◽  
Non Photochemical Quenching

Non–photochemical quenching of chlorophyll fluorescence (NPQ) is symptomatic of the regulation of energy dissipation by the light–harvesting antenna of photosystem II (PS II). The kinetics of NPQ in both leaves and isolated chloroplasts are determined by the transthylakoid ΔpH and the de–epoxidation state of the xanthophyll cycle. In order to understand the mechanism and regulation of NPQ we have adopted the approaches commonly used in the study of enzyme–catalysed reactions. Steady–state measurements suggest allosteric regulation of NPQ, involving control by the xanthophyll cycle carotenoids of a protonationdependent conformational change that transforms the PS II antenna from an unquenched to a quenched state. The features of this model were confirmed using isolated light–harvesting proteins. Analysis of the rate of induction of quenching both in vitro and in vivo indicated a bimolecular second–order reaction; it is suggested that quenching arises from the reaction between two fluorescent domains, possibly within a single protein subunit. A universal model for this transition is presented based on simple thermodynamic principles governing reaction kinetics.

scholarly journals Phosphorylation of chlamydomonas reinhardi chloroplast membrane proteins in vivo and in vitro.

1982 ◽  
Vol 93 (3) ◽  
pp. 712-718 ◽  
Author(s):  
G C Owens ◽  
I Ohad
Keyword(s):  
Membrane Proteins ◽  
Photosystem Ii ◽  
Binding Site ◽  
Reaction Center ◽  
Thylakoid Membrane ◽  
Red Light ◽  
Intact Cells ◽  
Turnover Process

Phosphorylation of thylakoid membrane proteins in the chloroplast of wild-type and mutant strains of Chlamydomonas reinhardi has been studied in vivo and in vitro. Intact cells or purified membranes were labeled with [32P]orthophosphate or [gamma-32P]ATP, respectively, and the presence of phosphorylated polypeptides was detected by autoradiography after membrane fractionation by SDS PAGE. The 32P was esterified to serine and threonine residues. At least six polypeptides were phosphorylated in vitro and in vivo, and corresponded to components of the photosystem II complex contributing to the formation of the light-harvesting-chlorophyll (LHC) a,b-protein complex, the DCMU binding site (32-35 kdaltons), and the reaction center (26 kdaltons). In agreement with previous reports (Alfonzo, et al., 1979, Plant Physiol., 65:730-734; and Bennett, 1979, FEBS (Fed. Eur. Biochem. Soc.) Lett., 103:342-344), the membrane-bound protein kinase was markedly stimulated by light in vitro via a mechanism requiring photosystem II activity. Phosphorylation of thylakoid membrane polypeptides in vivo was, however, completely independent of illumination. Similar amounts of phosphate were incorporated into the photosynthetic membranes of cells incubated in the dark, in white light with or without 3-(3,4-dichlorophenyl-1,1-dimethyl urea (DCMU), or in red or far-red light. Different turnovers of the phosphate were observed in the light and dark, and a phosphoprotein phosphatase involved in this turnover process was also associated with the membrane. Comparison of the amount of esterified phosphate per protein in vivo and the maximum incorporation in isolated membranes revealed that only a small fraction of the available sites could be phosphorylated in vitro. In contrast to the DCMU binding site, the LHC and 26-kdalton polypeptide were not phosphorylated in vivo when the reaction center II polypeptides of 44-54 kdaltons were missing. The finding that all the phosphoproteins appear to be components of the photosystem II complex and are only partially dephosphorylated in vivo suggests strongly that protein phosphorylation might play an important role in the maintenance of the organizational integrity of this complex. The observation that the LHC is not phosphorylated in the absence of the reaction center lends support to this idea.

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