Site of Action of Oxyfluorfen

Weed Science ◽  
1980 ◽  
Vol 28 (6) ◽  
pp. 640-645 ◽  
Author(s):  
M. K. Pritchard ◽  
G. F. Warren ◽  
R. A. Dilley
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Photosystem I ◽  
Electron Acceptor ◽  
Spinacia Oleracea ◽  
Membrane Damage ◽  
Green Beans ◽  
Site Of Action ◽  
Cyclic Electron Transfer ◽  
Electron Donation

The effects of oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] were studied on electron transport and phosphorylation in isolated spinach (Spinacia oleraceaL.) chloroplasts and on the response of green bean (Phaseolus vulgarisL. ‘Spartan Arrow’) to applications of oxyfluorfen alone or in combination with other herbicides. Coupled non-cyclic electron transfer and phosphorylation through photosystems I and II (H2O å methyl viologen) were inhibited about 30% and 55%, respectively, by 10−4M oxyfluorfen. Photosystem II-linked phosphorylation with dimethylbenzoquinone (2,5-dimethyl-p-benzoquinone) as the electron acceptor (H2O å DMQ) was completely inhibited by 10−4M oxyfluorfen. Photosystem II electron transport with dimethylbenzoquinone as the electron acceptor was inhibited 60% by 10−4M oxyfluorfen, whereas photosystem I electron transport with 2,6-dichlorophenol indophenol as electron donor (DCIPH2å MV) was not susceptible to oxyfluorfen inhibition. Photosystem I-linked phosphorylation and the accompanying electron transport supported by durohydroquinone electron donation (DQH2å MV) were inhibited about 50% by 10−4M oxyfluorfen, whereas cyclic phosphorylation was not inhibited at that concentration. Increased conductivity of a solution that contained leaf discs taken from green beans treated with various combinations of foliar-applied herbicides was a measure of membrane damage caused by the herbicides, and revealed that oxyfluorfen has a different site of action than do photosynthesis inhibitor and bipyridilium herbicides. Oxyfluorfen plus dinoseb (2-sec-butyl-4,6-dinitrophenol) injury to green beans was additive, but the two herbicides did not have the same site of action. Oxyfluorfen did not appear to inhibit electron transport in chloroplasts at herbicidal rates, nor was it dependent on electron transport for activation.

The site of electron transport inhibition by bentazon (3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2,2-dioxide) in isolated chloroplasts

1982 ◽  
Vol 60 (4) ◽  
pp. 409-412 ◽  
Author(s):  
Rungsit Suwanketnikom ◽  
Kriton K. Hatzios ◽  
Donald Penner ◽  
Duncan Bell
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Photosystem I ◽  
Electron Acceptor ◽  
Photosynthetic Electron Transport ◽  
Primary Electron ◽  
Photochemical Reactions ◽  
Spinacea Oleracea ◽  
Primary Electron Acceptor ◽  
Isolated Chloroplasts

The effect of bentazon (3-isopropyl-1H-2,1,3-benzathiadiazin-(4)3H-one 2,2-dioxide) on various photochemical reactions of isolated spinach (Spinacea oleracea L.) chloroplasts was studied at concentrations 0, 5, 15, 45, and 135 μM. Bentazon at a concentration of 135 μM strongly inhibited uncoupled electron transport from water to ferricyanide or to methylviologen with inhibition percentages greater than 90%. Photosystem II mediated electron transport from water to oxidized diaminodurene, with 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) blocking photosystem I, was also strongly inhibited by bentazon at 135 μM but less with lower concentrations of bentazon. Photosystem I mediated transfer of electrons from diaminodurene to methylviologen, with 3,4-dichlorophenyl-1,1-dimethylurea (DCMU) blocking photosystem II, was not inhibited by bentazon at any concentration examined. Transfer of electrons from catechol to methylviologen in hydroxylamine-treated chloroplasts was inhibited by bentazon, and the inhibition percentages were again concentration dependent. The data indicate that the site of bentazon inhibition of the photosynthetic electron transport is at the reducing side of photosystem II, between the primary electron acceptor Q and plastoquinone.

scholarly journals The effects of high concentrations of salts on photosynthetic electron transport in spinach (Spinacia oleracea) chloroplasts

1982 ◽  
Vol 204 (3) ◽  
pp. 705-712 ◽  
Author(s):  
A C Stewart
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Photosystem I ◽  
Spinacia Oleracea ◽  
Photosynthetic Electron Transport ◽  
Potassium Citrate ◽  
O2 Evolution ◽  
Hofmeister Series ◽  
Reaction Centre ◽  
High Concentrations

1. Photosynthetic electron transport from water to lipophilic Photosystem II acceptors was stimulated 3-5-fold by high concentrations (greater than or equal to 1 M) of salts containing anions such as citrate, succinate and phosphate that are high in the Hofmeister series. 2. In trypsin-treated chloroplasts, K3Fe(CN)6 reduction insensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea was strongly stimulated by high concentrations of potassium citrate, but there was much less stimulation of 2,6-dichloroindophenol reduction in Tris-treated chloroplasts supplied with 1,5-diphenylcarbazide as artificial donor. The results suggest that the main site of action of citrate was the O2-evolving complex of Photosystem II. 3. Photosystem I partial reactions were also stimulated by intermediate concentrations of citrate (up to 2-fold stimulation by 0.6-0.8 M-citrate), but were inhibited at the highest concentrations. The observed stimulation may have been caused by stabilizaton of plastocyanin that was complexed with the Photosystem I reaction centre, 4. At 1 M, potassium citrate protected O2 evolution against denaturation by heat or by the chaotropic agent NaNO3. 5. It is suggested that anions high in the Hofmeister series stimulated and stabilized electron transport by enhancing water structure around the protein complexes in the thylakoid membrane.

Inhibition of Photosystem II andChlorellaGrowth by 1-(m-t-butylacetamidophenyl)-3-methyl-3-methoxy urea

Weed Science ◽  
1979 ◽  
Vol 27 (2) ◽  
pp. 232-234 ◽  
Author(s):  
J. A. Swader ◽  
Celestia M. Howe
Keyword(s):  
Photosystem Ii ◽  
Water Splitting ◽  
Electron Donor ◽  
Photosystem I ◽  
Electron Acceptor ◽  
Spinacia Oleracea ◽  
Chlorella Sorokiniana ◽  
Phenylurea Herbicide ◽  
Isolated Chloroplasts

The experimental herbicide R-24191 [1-(m-t-butylacetamidophenyl)-3-methyl-3-methoxy urea] inhibited growth ofChlorella sorokinianaShihira and Kraus, O2evolution during CO2fixation byChlorellaand isolated leaf cells of spinach (Spinacia oleraceaL. ‘Winter Bloomsdale 769′), the photoreduction of NADP by isolated chloroplasts using water or hydroxylamine as the electron donor, the photoreduction of 2,6-dichloroindophenol by isolated chloroplasts, and O2uptake by isolated chloroplasts using paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) as the electron acceptor. The phenylurea herbicide had no effect on the last reaction when ascorbate plus 2,6-dichloroindophenol were used as the electron donor. The results indicate that the site of the phenylurea inhibition was in photosystem II between water-splitting and photosystem I.

The effect of alpha terthienyl on photosynthesis

1982 ◽  
Vol 60 (12) ◽  
pp. 2565-2569 ◽  
Author(s):  
John Sinclair ◽  
Thor Arnason
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Photosystem I ◽  
Electron Acceptor ◽  
Hill Reaction ◽  
Spinach Chloroplasts ◽  
Near Ultraviolet ◽  
A Site ◽  
The Hill ◽  
Clark Electrode

Alpha terthienyl (α-T), an allelopathic polyacetylene derivative occurring in the Asteraceae, was examined for its photosensitizing effect on respiration in Chlorella and photosynthesis in Chlorella and isolated spinach chloroplasts. In experiments with the Clark electrode, O2 evolution in saturating light with Chlorella was much more sensitive to α-T plus near ultraviolet (UV) treatments than respiration. O2 transients at the onset of illumination as measured with the modulated O2 polarograph were also inhibited by α-T plus near UV. The Hill reaction in uncoupled spinach chloroplasts using ferricyanide as electron acceptor is sensitive to photosensitization with α-T, but electron transport through photosystem I operating on its own showed no decrease in activity. The results are interpreted as an indication of a site of inhibition near photosystem II and possibly in CO2 fixation as well.

Effects of Diphenylether Herbicides on Reactions of Mitochondria and Chloroplasts

Weed Science ◽  
1970 ◽  
Vol 18 (5) ◽  
pp. 636-642 ◽  
Author(s):  
D. E. Moreland ◽  
W. J. Blackmon ◽  
H. G. Todd ◽  
F. S. Farmer
Keyword(s):  
Electron Transport ◽  
Oxygen Uptake ◽  
Spinacia Oleracea ◽  
White Potato ◽  
Light Reaction ◽  
Site Of Action ◽  
Transport Inhibitors ◽  
Atp Generation ◽  
A Site ◽  
Limited Oxygen

Effects of three diphenylether herbicides [2,4-dichlorophenyl-p-nitrophenyl ether (nitrofen); 2,4,6-trichlorophenyl-4′-nitrophenyl ether (hereinafter referred to as MC-1478); and 2,4′-dinitro-4-trifluoromethyl-diphenylether (hereinafter referred to as C-6989)] were measured on phosphorylation and electron transport in spinach(Spinacia oleraceaL.) chloroplasts, and mung bean(Phaseolus aureusL., var. Jumbo) and white potato tuber(Solarium tuberosumL.) mitochondria. All of the diphenylethers acted primarily as inhibitors of chloroplast noncyclic electron transport, and the coupled photophosphorylation. The compounds ranked in the following decreasing order of inhibitory effectiveness: MC-1478 ≥ C-6989 >> nitrofen. A site of action close to light reaction II was suggested. At high molar concentrations, marginal interference with cyclic electron transport or phosphorylation was obtained. In mitochondria, MC-1478 and nitrofen acted primarily as electron transport inhibitors with malate, NADH, and succinate as substrates. MC-1478 was a slightly stronger inhibitor than nitrofen. Only slight stimulation of ADP-limited oxygen uptake was obtained during the oxidation of NADH and succinate; whereas, strong inhibition of oxygen uptake was obtained with malate. C-6989 also weakly stimulated ADP-limited oxygen uptake with NADH and succinate but differed from the two chlorinated diphenylethers in that electron transport was not inhibited when ADP was present in excess. Interference with ATP generation could be one of the mechanisms through which the phytotoxicity of diphenylether herbicides is expressed.

Photoinhibition of Electron Transport Activity of Photosystem II in Isolated Thylakoids Studied by Thermoluminescence and Delayed Luminescence

1988 ◽  
Vol 43 (11-12) ◽  
pp. 871-876 ◽  
Author(s):  
Imre Vass ◽  
Narendranath Mohanty ◽  
Sándor Demeter
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Photosystem I ◽  
Half Life ◽  
Delayed Luminescence ◽  
Transport Activity ◽  
Primary Target ◽  
Electron Transport Activity ◽  
The Stability ◽  
Spinach Thylakoids

Abstract The effect of photoinhibition on the primary (QA) and secondary (QB) quinone acceptors of photosystem I I was investigated in isolated spinach thylakoids by the methods of thermoluminescence and delayed luminescence. The amplitudes of the Q (at about 2 °C) and B (at about 30 °C) thermoluminescence bands which are associated with the recombination of the S2QA- and S2QB charge pairs, respectively, exhibited parallel decay courses during photoinhibitory treatment. Similarly, the amplitudes of the flash-induced delayed luminescence components ascribed to the recombination of S20A and S2OB charge pairs and having half life-times of about 3 s and 30 s, respectively, declined in parallel with the amplitudes of the corresponding Q and B thermoluminescence bands. The course of inhibition of thermoluminescence and delayed luminescence intensity was parallel with that of the rate of oxygen evolution. The peak positions of the B and Q thermoluminescence bands as well as the half life-times of the corresponding delayed luminescence components were not affected by photoinhibition. These results indicate that in isolated thylakoids neither the amount nor the stability of the reduced OB acceptor is preferentially decreased by photoinhibition. We conclude that either the primary target of photodamage is located before the O b binding site in the reaction center of photosystem II or QA and OB undergo simultaneous damage.

Photosystem I-abhängige Phosphorylierung isolierter Chloroplasten mit Ascorbat/2.6-Dichlorphenolindophenol als Elektronendonator und Methylviologen als Elektronenakzeptor / Photosystem I Dependent Phosphorylation of Isolated Chloroplasts with Ascorbate/2,6-Dichlorophenolindophenol as Electron Donor and Methylviologen as Electron Acceptor

1972 ◽  
Vol 27 (4) ◽  
pp. 445-455 ◽  
Author(s):  
Heinrich Strotmann ◽  
Christa Von Gösseln
Keyword(s):  
Electron Transport ◽  
Linear System ◽  
Photosystem I ◽  
Electron Acceptor ◽  
Electron Flow ◽  
Phosphorylation Site ◽  
Cyclic System ◽  
Atp Production ◽  
Proton Uptake ◽  
Isolated Chloroplasts

Photosystem I related phosphorylation of isolated chloroplasts was investigated with special reference to the stoichiometry between ATP production and electron transprt (ATP: 2e⊖). The system studied contained DCMU to inhibit electron flow from photosystem II, ascorbate and DPIP to supply electrons to photosystem I, and methylviologen as electron acceptor. The following results were obtained:1. Basal electron transport is stimulated by the addition of the phosphorylating system, indicating that phosphorylation is really coupled to non-cyclic electron flow. The ratio ATP: 2e⊖ is 1, when the increase of electron flow obtained by the addition of ADP and phosphate is correlated to phosphorylation. This ratio is constant upon varying several parameters including DPIP concentration and light intensity.2. In the absence of methylviologen a DPIP catalyzed cyclic phosphorylation takes place (cf. I. c.7, 11, 12). Phosphorylation is not increased by the addition of methylviologen, indicating that both, the cyclic DPIP mediated and the non-cyclic system are coupled to the same phosphorylation site and limited by the same reaction step.3. In the absence of oxygen a methylviologen supported cyclic phosphorylation occurs. Comparing optimum rates, phosphorylation under these conditions is about twice as high as in the noncyclic system. Therefore we conclude that two phosphorylation sites are involved in methylviologen catalyzed cyclic electron transport. This system is sensitive against trypsin treatment of the chloroplasts, whereas the linear system is not.4. The two cyclic systems as well as the non-cyclic system are coupled to reversible proton uptake. Furthermore the linear system exhibits an irreversible uptake of hydrogen ions, which is stoichiometric to electron flow. From the reversible and the irreversible components of the pH changes the ratio of the proton pump to electron transprt can be calculated. Under steady state conditions the ration H⨁ : e⊖ approaches 1.

Studies about the Mechanism of Herbicidal Interaction with Photosystem II in Isolated Chloroplasts

1979 ◽  
Vol 34 (11) ◽  
pp. 1010-1014 ◽  
Author(s):  
Gernot Renger
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Excitation Energy ◽  
Electron Acceptor ◽  
Functional Organization ◽  
Regulatory Element ◽  
Release Kinetics ◽  
Acceptor Side ◽  
Receptor Sites ◽  
Isolated Chloroplasts

Abstract Based on the functional organization scheme of system-II-electron transport and its modification by different procedures a proteinaceous component enwrapping the redox components (plastoquinone molecules) of the acceptor side (thereby acting as regulatory element) is inferred to be the unique target for herbicidal interaction with system II. This proteinaceous component, which is attacked by trypsin, provides the receptor sites for the herbicides. Studies of the release kinetics in trypsinated chloroplasts of the inhibition of oxygen evolution with K3 [Fe (CN)6] as electron acceptor indicates, that there exists a binding area with different specific subreceptor sites rather than a unique binding site for the various types of inhibitors. Furthermore, trypsination of the proteinaceous component enhances the efficiency of the plastoquinone pool to act as a non-photochemical quencher for excitation energy.

DCMU-Induced Fluorescence Changes and Photodestruction of Pigments Associated with an Inhibition of Photosystem I Cyclic Electron Flow

1984 ◽  
Vol 39 (5) ◽  
pp. 351-353 ◽  
Author(s):  
Stuart M. Ridley ◽  
Peter Horton
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Photosystem I ◽  
Dose Response ◽  
Electron Flow ◽  
Cyclic Electron Flow ◽  
Cyclic Flow ◽  
Working Hypothesis ◽  
Dose Responses

Diuron (DCMU) induces the photodestruction of pigments, which is the initial herbicidal symptom. As a working hypothesis, it is proposed that this symptom can only be produced when the herbicide dose is sufficiently high to inhibit not only photosystem II electron transport almost completely, but also inhibit (through over oxidation) the natural cyclic electron flow associated with photosystem I as well. Using freshly prepared chloroplasts, studies of DCMU-induced fluorescence changes, and dose responses for inhibition of electron transport, have been compared with a dose response for the photodestruction of pigments in chloroplasts during 24 h illumination. Photodestruction of pigments coincides with the inhibition of cyclic flow.

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