Photosystem I cyclic electron transport: Measurement of ferredoxin-plastoquinone reductase activity

Cleland, Robert E.; Bendall, Derek S.

doi:10.1007/bf00029815

Cited by 100 publications

(45 citation statements)

References 39 publications

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“…2B, ANCOVA, P > 0.05, n = 3), well above the observed K i for inhibition of the antimycin A-sensitive pathway of CEF (51). These results imply that NDH, rather than the PGR5/PGRL1 pathway, is the predominant route for elevated CEF in GO5, and are also in accord with the observed increased postillumination rise (Fig.…”

Section: Effects Of H 2 O 2 Production By Plants Expressing Glycolatesupporting

confidence: 78%

Activation of cyclic electron flow by hydrogen peroxide in vivo

Strand

Livingston

Satoh-Cruz

et al. 2015

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

119

116

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Cyclic electron flow (CEF) around photosystem I is thought to balance the ATP/NADPH energy budget of photosynthesis, requiring that its rate be finely regulated. The mechanisms of this regulation are not well understood. We observed that mutants that exhibited constitutively high rates of CEF also showed elevated production of H 2 O 2 . We thus tested the hypothesis that CEF can be activated by H 2 O 2 in vivo. CEF was strongly increased by H 2 O 2 both by infiltration or in situ production by chloroplastlocalized glycolate oxidase, implying that H 2 O 2 can activate CEF either directly by redox modulation of key enzymes, or indirectly by affecting other photosynthetic processes. CEF appeared with a half time of about 20 min after exposure to H 2 O 2 , suggesting activation of previously expressed CEF-related machinery. H 2 O 2 -dependent CEF was not sensitive to antimycin A or loss of PGR5, indicating that increased CEF probably does not involve the PGR5-PGRL1 associated pathway. In contrast, the rise in CEF was not observed in a mutant deficient in the chloroplast NADPH:PQ reductase (NDH), supporting the involvement of this complex in CEF activated by H 2 O 2 . We propose that H 2 O 2 is a missing link between environmental stress, metabolism, and redox regulation of CEF in higher plants. I n oxygenic photosynthesis, linear electron flow (LEF) is the process by which light energy is captured to drive the extraction of electrons and protons from water and transfer them through a system of electron carriers to reduce NADPH. LEF is coupled to proton translocation into the thylakoid lumen, generating an electrochemical gradient of protons ðΔμ H +Þ or proton motive force (pmf). The pmf drives the synthesis of ATP to power the reactions of the Calvin-Benson-Bassham (CBB) cycle and other essential metabolic processes in the chloroplast. The pmf is also a key regulator of photosynthesis in that it activates the photoprotective q E response to dissipate excess light energy and downregulates electron transfer by controlling the rate of oxidation of plastoquinol at the cytochrome b 6 f complex (b 6 f), thus preventing the buildup of reduced intermediates (1, 2).LEF results in the transfer or deposition into the lumen of three protons for each electron transferred through PSII, plastoquinone (PQ), b 6 f, plastocyanin, and photosystem I (PSI) to ferredoxin (Fd). The synthesis of one ATP is thought to require the passage of 4.67 protons through the ATP synthase, so that LEF should produce a ratio of ATP/NADPH of about 1.33; this ratio is too low to sustain the CBB cycle or supply ATP required for translation, protein transport, or other ATP-dependent processes (3). In addition, the relative demands for ATP and NADPH can change dramatically depending on environmental, developmental, and other factors, leading to rapid energy imbalances that require dynamical regulation of ATP/NADPH balance.Several alternative electron flow pathways in the chloroplast have been proposed to augment ATP production, thus balancing the ATP/NADPH ...

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Section: Effects Of H 2 O 2 Production By Plants Expressing Glycolatesupporting

confidence: 78%

Activation of cyclic electron flow by hydrogen peroxide in vivo

Strand

Livingston

Satoh-Cruz

et al. 2015

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

119

116

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“…This binding must act as a trigger to induce the modification of the protein structure. The decreased fluorescence intensity in the presence of heparin and TTFA, which are known to bind with FNR (31)(32)(33)(34), indicates that some effect of these inhibitors on the structure of FNR is similar compared to NADP + . On the other hand, NADPH, likely through its own binding to FNR, removed the action of NADP + .…”

Section: Discussionmentioning

confidence: 99%

Control of Energy Dissipation and Photochemical Activity in Photosystem I by NADP-Dependent Reversible Conformational Changes

et al. 2003

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Addition of NADP + to thylakoid membranes or isolated photosystem I (PSI) submembrane fractions quenched chlorophyll fluorescence by up to 40% at low or room temperature. This quenching was reversed by NADPH. Similar quenching was also observed with the addition of heparin or thenoyltrifluoroacetone (TTFA), inhibitors that bind ferredoxin:NADP + reductase (FNR) and prevent reduction of NADP + . The NADP + -induced quenching coincided with a reversible conformational change of the secondary protein structure in the PSI submembrane fractions where 20% of the R-helix conformations were transformed mainly into -sheet-like structures. Further, P700 photooxidation was retarded due to this conformational change, and about 25% of the centers could not be photooxidized, these changes being also reversible with addition of NADPH. The above modifications in the presence of NADP + also increased photodamage processes under strong illumination, and NADPH protected it. Conformational modification of FNR upon binding of NADP + or NADPH is proposed to trigger the macromolecular changes in a larger part of the protein complex of PSI. The conformational changes must increase the intermolecular distances and change the mutual orientation between the various cofactors in the PSI complex. This new control mechanism of energy dissipation and photochemical activity by NADP + / NADPH is proposed to increase the turnover rate of PSI under conditions when both linear and cyclic electron transport activities must be supported.In chloroplasts of higher plants and algae, photosystem I (PSI) 1 catalyzes the light-driven electron transport between plastocyanin and ferredoxin. The enzyme ferredoxin:NADP + reductase (FNR) is required for the reduction of NADP + to NADPH in a reaction that uses two molecules of reduced ferredoxin. PSI is formed of a core complex composed of an heterodimer of the PsaA/PsaB polypeptides surrounded by the peripheral chlorophyll (Chl) a/b binding proteins (LHCI) and at least 12 other polypeptide subunits (1, 2). The reaction center of PSI, P700, is located in the PsaA/ PsaB protein complex with the primary electron acceptors and about 90-100 Chl and 15-22 -carotene molecules as determined for higher plants and cyanobacteria (1, 3). LHCI is composed of two subcomplexes, LHCI-680 that consists of two polypeptides of 23 kDa (Lhca2) and 25 kDa (Lhca3), respectively, and LHCI-730 that also comprises two polypeptides of 22 kDa (Lhca1) and 21 kDa (Lhca4), respectively (4, 5).The rate of electron transport within PSI is mainly controlled by the flux of electrons transferred from photosystem II (PSII) through the cytochrome b 6 /f complex and by the activity of dark carbon metabolism that uses NADPH formed at the acceptor side of PSI (6-9). It is also known that the ATP/NADPH ratio can be modulated by the onset of cyclic electron transport around PSI, which produces ATP without the reduction of NADP + molecules (10). Thus an increased chloroplastic concentration of NADPH is proposed to poise the redox state of the ...

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“…A role of the Ndh complex in cyclic electron flow around PS I was recently confirmed by photoacoustic measurements performed in tobacco ndh mutants (12). It should be noted that alternate activities, such as a putative ferredoxin-PQ reductase (FQR) (13,14) or a Ndh-2 type activity may also be involved in these processes (15,16).…”

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confidence: 84%

Involvement of a Plastid Terminal Oxidase in Plastoquinone Oxidation as Evidenced by Expression of the Arabidopsis thaliana Enzyme in Tobacco

Joët¹,

Genty²,

Josse³

et al. 2002

Journal of Biological Chemistry

150

156

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Chlororespiration has been defined as a respiratory electron transport chain in interaction with photosynthetic electron transport involving both non-photochemical reduction and oxidation of plastoquinones. Different enzymatic activities, including a plastidencoded NADH dehydrogenase complex, have been reported to be involved in the non-photochemical reduction of plastoquinones. However, the enzyme responsible for plasquinol oxidation has not yet been clearly identified. In order to determine whether the newly discovered plastid oxidase (PTOX) involved in carotenoid biosynthesis acts as a plastoquinol oxidase in higher plant chloroplasts, the Arabidopsis thaliana PTOX gene (At-PTOX) was expressed in tobacco under the control of a strong constitutive promoter. We showed that At-PTOX is functional in tobacco chloroplasts and strongly accelerates the non-photochemical reoxidation of plastoquinols; this effect was inhibited by propyl gallate, a known inhibitor of PTOX. During the dark to light induction phase of photosynthesis at low irradiances, At-PTOX drives significant electron flow to O 2 , thus avoiding over-reduction of plastoquinones, when photosynthetic CO 2 assimilation was not fully induced. We proposed that PTOX, by modulating the redox state of intersystem electron carriers, may participate in the regulation of cyclic electron flow around photosystem I.

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Photosystem I cyclic electron transport: Measurement of ferredoxin-plastoquinone reductase activity

Cited by 100 publications

References 39 publications

Activation of cyclic electron flow by hydrogen peroxide in vivo

Activation of cyclic electron flow by hydrogen peroxide in vivo

Control of Energy Dissipation and Photochemical Activity in Photosystem I by NADP-Dependent Reversible Conformational Changes

Involvement of a Plastid Terminal Oxidase in Plastoquinone Oxidation as Evidenced by Expression of the Arabidopsis thaliana Enzyme in Tobacco

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