Restoration by silicotungstic acid of DCMU-inhibited photoreactions in spinach chloroplasts

Girault, G.; Galmiche, J.M.

doi:10.1016/0005-2728(74)90014-0

Cited by 35 publications

(5 citation statements)

References 5 publications

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“…In agreement with the electron transport data (Table I), addition of ferricyanide slowed the rise in fluorescence yield in the WT (14), but had no effect on the fluorescence curve of the mutant. Further evidence for the site of the block in the mutant was provided by analyzing the photoreduction of the lipophilic electron acceptors DAD and phenylenediamine (11,19) and of silicomolybdate (4,5,8); the first two were reported to accept electrons at the level of plastoquinone and the last at the level of Q. The addition of these electron acceptors to mutant chloroplasts increased the low rate of ferricyanide reduction to rates similar to those of WT (Table II).…”

Section: Resultsmentioning

confidence: 99%

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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: 99%

“…The former has been shown to be due to a direct reduction by Q (4,5,8), and the latter to reduction at the site of plastoquinone (11). The fact that Cyt f of the mutant is not reduced by red light but is oxidized by red or far red (Fig.…”

Section: Discussionmentioning

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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“…As was shown by Girault and Galmiche (1974), Giaquinta et al (1974), and Barr et al (1975), silieotungstate and silicomolybdate mediate a DCMUinsensitive Hill reaction. It was concluded by the latter authors and substantiated by the work of Giaquinta and Dilley (1975), and of Zilinskas and Govindjee (1975) that silicomolybdate is reduced at or close to the primary quencher Q of photosystem 11.…”

Section: Introductionmentioning

confidence: 71%

“…Therefore, their biochemistry is of great interest for the study of partial redox reactions of the photosynthetic electron transport chain. We resumed the studies on the reaction site(s) of silicomolybdic acid, but our findings led to conclusions contrary to those of Girault and Galmiche (1974) and Berg and Izawa (1977).…”

Section: Introductionmentioning

confidence: 94%

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Replacement of photosynthetic electron transport inhibitors by silicomolybdate

Böger¹

1982

Physiologia Plantarum

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KCN‐treated spinach chloroplasts, their photosystem I being ineffective, exhibit a single reaction site for silicomolybdate. Using this heteropolyanion as electron acceptor, photosynthetic oxygen evolution is partially inhibited by ureas, triazines, or phenylpyridazinone herbicides, their inhibitory effect depending on the concentration of silicomolybate. Labelled atrazine attached to isolated chloroplast material is competitively replaced by silicomolybdate in the same manner as e.g. ureas complete with a triazine herbicide. – It is concluded (1) that silicomolybdate is bound and reduced at the herbicide‐binding protein, and (2) that the inhibition of silicomolybdate reduction by herbicides such as DCMU is due to loss of reaction sites for silicomolybdate.

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Artificial Acceptors and Donors

Hauska¹

1977

Photosynthesis I

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Restoration by silicotungstic acid of DCMU-inhibited photoreactions in spinach chloroplasts

Cited by 35 publications

References 5 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

Replacement of photosynthetic electron transport inhibitors by silicomolybdate

Artificial Acceptors and Donors

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