Coregulation of electron transport through PS I by Cyt b 6 f, excitation capture by P700 and acceptor side reduction. Time kinetics and electron transport requirement

Laisk, Agu; Oja, Vello

doi:10.1007/bf00032231

Cited by 15 publications

(6 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The ensuing decline in DpH would decrease the resistance to plastoquinol oxidation by Cyt b 6 f allowing an increased¯ow of electrons to P700 + (Harbinson and Hedley 1989;Foyer et al 1990). The decline in levels of P700 + at very low C i levels is due to blockage of P700 photooxidation by reduced acceptors (Laisk and Oja 1995). Nevertheless, the relative increase in oxidation of the PSI donor in the mutant compared to the WT is highest under these conditions, consistent with dierential eects on inter-photosystem electron transport.…”

Section: Discussionsupporting

confidence: 51%

Photosynthetic properties of an Arabidopsis thaliana mutant possessing a defective PsbS gene

2001

Planta

View full text Add to dashboard Cite

We describe the properties of npq4-9, a new mutant of Arabidopsis thaliana (L.) Heynh. with reduced nonphotochemical quenching (NPQ) capacity that possesses a single amino acid substitution in the PsbS gene encoding PSII-S, a ubiquitous pigment-binding protein associated with photosystem II (PSII) of higher plants. Growth, photosynthetic pigment contents, and levels of the major PSII antenna proteins were not affected by npq4-9. Although the extent of de-epoxidatin of violaxanthin to antheraxanthin plus zeaxanthin for leaves displaying the mutant phenotype equaled or exceeded that observed for the wild type, the relative effectiveness of de-epoxidized xanthophylls in promoting NPQ was consistently lower for the mutant. Energy partitioning in PSII was analyzed in terms of the competition for singlet chlorophyll a among the processes of fluorescence, thermal dissipation, and photochemistry. The key processes of NPQ and photochemistry in open PSII centers are represented by the relative in vivo rate constants kN and kP0, respectively. The magnitude of kP0 in normal leaves declined only slightly with increasing kN, consistent with localization of NPQ primarily in the antenna complex. Conversely, a highly significant linear decline in kP0 with increasing kN was observed for the mutant, consistent with a role for the PSII reaction center in the NPQ mechanism. Although the PSII absorption cross-section for white light was not significantly different relative to that of the wild type, PSII quantum yield was significantly lower in the mutant. The resulting lower capacity for linear electron transport in the mutant primarily affected reduction of terminal acceptors other than CO2. Parallel measurements of fluorescence and in vivo absorbance at 820 nm indicated a consistently higher steady-state level of reduction of PSII acceptors and accumulation of P700+ for the mutant. This suggests that inter-photosystem electron transport in the mutant is restricted either by a higher transthylakoid delta pH or by diminished accessibility to reduced plastoquinone.

show abstract

Section: Discussionsupporting

confidence: 51%

Photosynthetic properties of an Arabidopsis thaliana mutant possessing a defective PsbS gene

2001

Planta

View full text Add to dashboard Cite

show abstract

“…In intact leaves, photosynthetic control down-regulated PQH 2 oxidation by Cyt b 6 f turnover, but incompletely (from 200 down to 40 s -1 , Laisk and Oja 1994). Later, we observed that this control became stronger by increasing the time of exposure to limiting CO 2 concentration to 15 min (Laisk and Oja 1995). Such a slow onset of photosynthetic control was difficult to explain in terms of DpH that is expected to increase much faster.…”

Section: Participation Of Ferredoxin-nadp Reductasementioning

confidence: 78%

“…The observed residual rate of 40 s -1 (Laisk and Oja 1994) agrees well with the CET rate in our present experiments. The slow temporal changes observed at strictly rate-limiting CO 2 concentrations (Laisk and Oja 1995) most likely reflected the slow decay of the CET donor pool during the extended exposure to very low CO 2 (see also Joliot and Joliot 2006).…”

Section: Participation Of Ferredoxin-nadp Reductasementioning

confidence: 96%

Fast cyclic electron transport around photosystem I in leaves under far-red light: a proton-uncoupled pathway?

et al. 2009

Self Cite

View full text Add to dashboard Cite

Fast cyclic electron transport (CET) around photosystem I (PS I) was observed in sunflower (Helianthus annuus L.) leaves under intense far-red light (FRL) of up to 200 mumol quanta m(-2) s(-1). The electron transport rate (ETR) through PS I was found from the FRL-dark transmittance change at 810 and 950 nm, which was deconvoluted into redox states and pool sizes of P700, plastocyanin (PC) and cytochrome f (Cyt f). PC and P700 were in redox equilibrium with K(e) = 35 (ΔE(m) = 90 mV). PS II ETR was based on O(2) evolution. CET [(PS I ETR) - (PS II ETR)] increased to 50-70 mumol e(-) m(-2) s(-1) when linear electron transport (LET) under FRL was limited to 5 mumol e(-) m(-2) s(-1) in a gas phase containing 20-40 mumol CO(2) mol(-1) and 20 mumol O(2) mol(-1). Under these conditions, pulse-saturated fluorescence yield F(m) was non-photochemically quenched; however, F(m) was similarly quenched when LET was driven by low green or white light, which energetically precluded the possibility for active CET. We suggest that under FRL, CET is rather not coupled to transmembrane proton translocation than the CET-coupled protons are short-circuited via proton channels regulated to open at high ΔpH. A kinetic analysis of CET electron donors and acceptors suggests the CET pathway is that of the reversed Q-cycle: Fd -> (FNR) -> Cyt c(n) -> Cyt b(h) -> Cyt b(l) -> Rieske FeS -> Cyt f -> PC -> P700 ->-> Fd. CET is activated when PQH(2) oxidation is opposed by high ΔpH, and ferredoxin (Fd) is reduced due to low availability of e(-) acceptors. The physiological significance of CET may be photoprotective, as CET may be regarded as a mechanism of energy dissipation under stress conditions.

show abstract

“…The model did not well reproduce the ''photosynthetic control'' of the Cyt b 6 f turnover by the thermodynamic backpressure of protons (Siggel 1974), suggesting that the regulatory process may not be kinetic, but structural, e.g. one driven by the PSI acceptor side reduction (Johnson 2003) and related to the movement of Cyt b 6 f complexes in thylakoids (Vallon et al 1991;Laisk and Oja 1995) or to the dimerization of Cyt b 6 f complexes (Cramer et al 1996;Heimann et al 1998). A formal pK of the Cyt b 6 f control (Cruz et al 2001) would solve the problem at light saturation, but it would not reproduce the observed down-regulation of Cyt b 6 f at light limitation (Laisk et al 2005).…”

Section: Heuristic Results and Prospectsmentioning

confidence: 96%

C3 photosynthesis in silico

2006

Self Cite

View full text Add to dashboard Cite

A computer model comprising light reactions, electron-proton transport, enzymatic reactions, and regulatory functions of C3 photosynthesis has been developed as a system of differential budget equations for intermediate compounds. The emphasis is on electron transport through PSII and PSI and on the modeling of Chl fluorescence and 810 nm absorptance signals. Non-photochemical quenching of PSII excitation is controlled by lumenal pH. Alternative electron transport is modeled as the Mehler type O2 reduction plus the malate-oxaloacetate shuttle based on the chloroplast malate dehydrogenase. Carbon reduction enzymes are redox-controlled by the ferredoxin-thioredoxin system, sucrose synthesis is controlled by the fructose 2,6-bisphosphate inhibition of cytosolic FBPase, and starch synthesis is controlled by ADP-glucose pyrophosphorylase. Photorespiratory glycolate pathway is included in an integrated way, sufficient to reproduce steady-state rates of photorespiration. Rate-equations are designed on principles of multisubstrate-multiproduct enzyme kinetics. The parameters of the model were adopted from literature or were estimated from fitting the photosynthetic rate and pool sizes to experimental data. The model provided good simulations for steady-state photosynthesis, Chl fluorescence, and 810 nm transmittance signals under varying light, CO2 and O2 concentrations, as well as for the transients of post-illumination CO2 uptake, Chl fluorescence induction and the 810 nm signal. The modeling shows that the present understanding of photosynthesis incorporated in the model is basically correct, but still insufficient to reproduce the dark-light induction of photosynthesis, the time kinetics of non-photochemical quenching, 'photosynthetic control' of plastoquinone oxidation, cyclic electron flow around PSI, oscillations in photosynthesis. The model may find application for predicting the results of gene transformations, the analysis of kinetic experimental data, the training of students.

show abstract

Coregulation of electron transport through PS I by Cyt b 6 f, excitation capture by P700 and acceptor side reduction. Time kinetics and electron transport requirement

Cited by 15 publications

References 22 publications

Photosynthetic properties of an Arabidopsis thaliana mutant possessing a defective PsbS gene

Photosynthetic properties of an Arabidopsis thaliana mutant possessing a defective PsbS gene

Fast cyclic electron transport around photosystem I in leaves under far-red light: a proton-uncoupled pathway?

C3 photosynthesis in silico

Contact Info

Product

Resources

About