Energy‐Dependent Reverse Electron Flow in Chloroplasts

Rienits, K.G.; Hardt, Haim; Avron, Mordhay

doi:10.1111/j.1432-1033.1974.tb03412.x

Cited by 42 publications

(11 citation statements)

References 14 publications

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“…between photosystem II and Cyt f). Finally, a block at this site should inhibit the ATP-driven reverse electron flow activity (18). Wild-type chloroplasts exhibited ATP-driven reverse electron flow to an extent similar to that observed in lettuce chloroplasts (20-30% reduction of Q), while mutant chloroplasts were totally inactive.…”

Section: Resultsmentioning

confidence: 79%

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Evidence for a Block between Plastoquinone and Cytochrome f in a Photosynthetic Mutant of Lemna with Abnormal Flowering Behavior

Shahak¹,

Posner²,

Avron³

1976

Plant Physiol.

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Mutant strain 1073 of Lemna perpusilla is conduded to be blocked between plastoquinone and cytochromef in the photosynthetic electron transport system. The location of the block is based on the following observations of activities in chloroplasts isolated from the mutant and wild-type plants. (a) Relative to wild type, electron flow rates from water to ferricyanide, 2,6-dichlorophenol indophenol or NADP were very low in the mutant, but rates of photosystem I-dependent electron flow and cydic phosphorylation were high. Chloroplasts were prepared from Lemna and lettuce as previously described (2), except for the addition of 0.5 mg/ml of BSA to the grinding and washing media and 10 mg/ml to the resuspension medium (7). Chl concentration was determined according to Arnon (1). The reduction of ferricyanide, DCPIP, or NADP was measured in a Cary 14 spectrophotometer with an attachment to reduce scattering effects. Oxygen uptake was measured with a Yellow Springs Instrument Clark type 02 electrode. ATP formation was assayed as described (2). Chl fluorescence induction and ATP-driven reverse electron flow (18) RESULTSThe ability of mutant 1073 to photoreduce several electron acceptors in reactions requiring excitation of photosystem II, photosystem I, or both is given in Table I. Electron transport from water to ferricyanide, DCPIP, or NADP was very poor in the mutant chloroplasts relative to the WT or to lettuce. The rates of ferricyanide reduction in the WT or lettuce chloroplasts were stimulated 2-to 3-fold by the addition of the uncoupler methylamine, whereas the rate in the mutant chloroplasts was unaffected, indicating that the block was not located in the energy-converting system. In the photosystem I-sensitized electron transport from reduced DAD to 02 (9), the mutant was about as effective as the WT. Consistent with the above results, mutant chloroplasts were inactive in photophosphorylation coupled to electron flow from water to ferricyanide but were active in PMS-catalyzed cyclic photophosphorylation. The major block was therefore in the electron transport system close to photosystem II. To determine whether the block was located before, at, or after photosystem II, Chl fluorescence induction was followed. Figure 1 shows that the WT and mutant had essentially identical fluorescence induction curves, which were similarly affected by the addition of DCMU. The dark recovery of the variable fluorescence yield was also similar in the wild type and mutant (not shown). Since the rise in the variable fluorescence yield upon illumination is thought to be due to the electron transport system from water to and including the "pool" of electron acceptors (14), mainly plastoquinone, it is clear from the latter observa-577 www.plantphysiol.org on May 8, 2018 -Published by Downloaded from

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Section: Resultsmentioning

confidence: 79%

“…ATP formation was assayed as described (2). Chl fluorescence induction and ATP-driven reverse electron flow (18) were measured in the apparatus constructed by Malkin (15).…”

mentioning

confidence: 99%

Evidence for a Block between Plastoquinone and Cytochrome f in a Photosynthetic Mutant of Lemna with Abnormal Flowering Behavior

Shahak¹,

Posner²,

Avron³

1976

Plant Physiol.

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“…This demonstrates 259 that there is no reduction of the PQ pool and of the primary acceptor QA by a ApH-induced back electron flow. Indeed, such a back transfer occurs only in the presence of reductants and redox mediators (Rienits et al 1974;Schreiber 1984).…”

Section: Discussionmentioning

confidence: 99%

Effects of dark- and light-induced proton gradients in thylakoids on the Q and B thermoluminescence bands

Miranda

Ducruet

1995

Photosynth Res

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Thermoluminescence experiments have been carried out to study the effect of a transmembrane proton gradient on the recombination properties of the S2 and S3 states of the oxygen evolving complex with QA (-) and QB (-), the reduced electron acceptors of Photosystem II. We first determined the properties of the S2QA (-) (Q band), S2QB (-) and S3QB (-) (B bands) recombinations in the pH range 5.5 to 9.0, using uncoupled thylakoids. The, a proton gradient was created in the dark, using the ATP-hydrolase function of ATPases, in coupled unfrozen thylakoids. A shift towards low temperature of both Q and B bands was observed to increase with the magnitude of the proton gradient measured by the fluorescence quenching of 9-aminoacridine. This downshift was larger for S3QB (-) than for S2QB (-) and it was suppressed by nigericin, but not by valinomycin. Similar results were obtained when a proton gradient was formed by photosystem I photochemistry. When Photosystem II electron transfer was induced by a flash sequence, the reduction of the plastoquinone pool also contributed to the downshift in the absence of an electron acceptor. In leaves submitted to a flash sequence above 0°C, a downshift was also observed, which was supressed by nigericin infiltration. Thus, thermoluminescence provides direct evidence on the enhancing effect of lumen acidification on the S3→S2 and S2→S1 reverse-transitions. Both reduction of the plastoquinone pool and lumen acidification induce a shift of the Q and B bands to lower temperature, with a predominance of lumen acidification in non-freezing, moderate light conditions.

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“…After light activation of the latent adenosine triphosphatase (ATPase), addition of ATP in the dark drives reverse electron flow in isolated chloroplasts as evidenced by the oxidation of cytochrome f and the reduction of Q [ 1,2]. According to the chemiosmotic hypothesis [3] proton gradients should be obligatory energy transducing intermediates in this process.…”

Section: Introductionmentioning

confidence: 99%

Proton gradients as possible intermediary energy transducers during ATP‐driven reverse electron flow in chloroplasts

Avron

Schreiber

1977

FEBS Letters

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Energy‐Dependent Reverse Electron Flow in Chloroplasts

Cited by 42 publications

References 14 publications

Evidence for a Block between Plastoquinone and Cytochrome f in a Photosynthetic Mutant of Lemna with Abnormal Flowering Behavior

Evidence for a Block between Plastoquinone and Cytochrome f in a Photosynthetic Mutant of Lemna with Abnormal Flowering Behavior

Effects of dark- and light-induced proton gradients in thylakoids on the Q and B thermoluminescence bands

Proton gradients as possible intermediary energy transducers during ATP‐driven reverse electron flow in chloroplasts

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