Interference by Herbicides with the Transmembrane Potential of Thylakoids

1987 ◽  
Vol 42 (6) ◽  
pp. 718-726 ◽  
Author(s):  
Donald E. Moreland ◽  
William P. Novitzky
Keyword(s):  
Electron Transport ◽  
Thylakoid Membrane ◽  
Transmembrane Potential ◽  
Proton Motive Force ◽  
Cyclic Electron Transport ◽  
Low Concentrations ◽  
High Concentrations ◽  
Proton Shuttling ◽  
Electrical Components ◽  
Spinach Thylakoids

Interferences expressed by herbicides classified as inhibitory uncouplers were measured on the induction and maintenance of ΔpH and ΔΨ, the chemical and electrical components, respectively. of the proton motive force (pmf) generated by light-induced cyclic electron transport in spinach thylakoids. Maintenance of the pmf is required for the synthesis of ATP. The inhibitory uncouplers arc known to inhibit photophosphorylation, but the mechanisms involved remain to be identified. The dinoseb types (dinitrophenols. benzimidazoles. benzonitriles. bromophenoxim. perfluidone. thiadiazoles) of inhibitory uncouplers, most of which contain dissociable protons, were found to discharge ΔpΗ at low concentrations and to collapse ΔΨ at high concentrations. Collapse of ΔpΗ can be attributed to the protonophoric (proton shuttling) action of the herbicides. However, collapse of ΔΨ can be caused by alterations induced to the integrity and loss of semipermeability of the thylakoid membrane. As a result the membrane bccomes permeable to protons and other cations, and the electrical charges across the membrane are neutralized. The non-ionic dicryl types of inhibitory uncouplers (acylanilides. dinitroanilines. diphenylethcrs. bis-carbamates) collapsed ΔΨ at concentrations that were somewhat lower than those required for the collapse of ΔpΗ. These herbicides appear only to alter the integrity and permeability of the thylakoid membrane. Inhibition of photophosphorylation by the inhibitory uncouplcrs correlated with their ability to dissipate the pmf.

Effect of the Plastoquinone Antagonist Dibromothymoquinone on Electron Transport Reactions in Chloroplast Preparations

1977 ◽  
Vol 4 (2) ◽  
pp. 253 ◽  
Author(s):  
A Stewart ◽  
AWD Larkum
Keyword(s):  
Electron Transport ◽  
Thylakoid Membrane ◽  
Methyl Viologen ◽  
Control Level ◽  
Type A ◽  
Low Concentrations ◽  
Intact Chloroplasts ◽  
Photosynthetic Control ◽  
Type C

The effects of dibromothymoquinone (DBMIB) on electron transport in types A, B, C and D spinach and pea chloroplast preparations have been studied. DBMIB (1 x 10-6M) strongly inhibited electron transport to methyl viologen in all the types of chloroplasts, while electron transport to ferricyanide was inhibited by 60%. Envelope-free (type C) chloroplast preparations with poor photosynthetic control were inhibited more strongly than intact (types A and B) chloroplast preparations at low (< 5 x 10-7M) concentrations of DBMIB. Type C preparations with good photosynthetic control were less strongly inhibited except in the presence of uncoupler or in the absence of ADP. Above 1 x 10-6M DBMIB, inhibition of electron transport to ferricyanide became progressively less and, with type A chloroplast preparations, a large stimulation compared to the control level occurred. Phenylenediamine stimulated high rates of electron transport to ferricyanide in the presence of low concentrations of DBMIB. At higher DBMIB concentrations, the stimulation was completely reversed and envelope-free chloroplasts again showed greater sensitivity to DBMIB compared to intact chloroplasts. DBMIB appears to have a number of sites of interaction with the thylakoid membrane.

Polypeptides of the Thylakoid Membrane and Their Functional Characterization

1978 ◽  
Vol 33 (9-10) ◽  
pp. 723-730 ◽  
Author(s):  
Georg H. Schmid ◽  
Wilhelm Menke ◽  
Alfons Radunz ◽  
Friederike Koenig
Keyword(s):  
Molecular Weight ◽  
Electron Transport ◽  
Electron Donor ◽  
Photosystem I ◽  
Thylakoid Membrane ◽  
Apparent Molecular Weight ◽  
Variable Fluorescence ◽  
Phenazine Methosulfate ◽  
Cyclic Photophosphorylation ◽  
High Concentrations

Abstract From stroma-freed chloroplasts of Antirrhinum majus polypeptides with the apparent molecular weights 44 000, 26 000 and 20 000 were isolated.The antiserum to a polypeptide with the moleculair weight 44 000 inhibits the photoreduction of anthraquinone-2-sulfonate with dichlorophenol indophenol/ascorbate when the concentration of the electron donor dichlorophenol indophenol is low. The antiserum enhances the rate of phenazine methosulfate-mediated cyclic photophosphorylation. The variable fluorescence yield is increased by the antiserum . It is assumed that this polypeptide plays a role in electron transport between the two photosystems. From two polypeptides with the apparent molecular weight 26 000 one seems to belong to the reaction center of photosystem II as it inhibits the photooxidation of tetramethyl benzidine and diphenyl carbazide with suitable electron acceptors and inhibits electron transport between water and silicomolybdate. Variable fluorescence is not or not too strong decreased by the antiserum . The other polypeptide of the apparent molecular weight 26 000 inhibits the photoreduction of anthraquinone-2-sulfonate with high concentrations of dichlorophenol indophenol as the electron donor. Phenazine methosulfate-mediated cyclic photophosphorylation is also inhibited by the antiserum . Therefore, we should like to associate it with the reaction center of photosystem I. The antiserum to the polypeptide with the apparent molecular weight 20 000 inhibits the photoreduction of anthraquinone-2-sulfonate with low and high concentrations of the electron donor dichlorophenol indophenol. It enhances phenazine methosulfate-mediated cyclic photophosphorylation. The polypeptide, therefore, should be functionally involved on the acceptor side of photosystem I.The results obtained up-to-now on the function and localization of the polypeptides in the thylakoid membrane are summarized.

scholarly journals Regulation of NAD(P)H Dehydrogenase-Dependent Cyclic Electron Transport Around PSI by NaHSO3 at Low Concentrations in Tobacco Chloroplasts

2011 ◽  
Vol 52 (10) ◽  
pp. 1734-1743 ◽  
Author(s):  
Yanxia Wu ◽  
Fangfang Zheng ◽  
Weimin Ma ◽  
Zhiguo Han ◽  
Qun Gu ◽  
...  
Keyword(s):  
Electron Transport ◽  
Cyclic Electron Transport ◽  
Low Concentrations

Interference by Herbicidal Inhibitors of Electron Transport with Phosphorylation and Permeability Properties of Chloroplast Membranes

1984 ◽  
Vol 39 (5) ◽  
pp. 329-334 ◽  
Author(s):  
Donald E. Moreland ◽  
William P. Novitzky
Keyword(s):  
Electron Transport ◽  
Thylakoid Membrane ◽  
Chloroplast Envelope ◽  
Ortho Position ◽  
Response Patterns ◽  
Chloroplast Membranes ◽  
Semipermeable Membranes ◽  
Low Concentrations ◽  
Maximum Inhibition ◽  
Transport Inhibitors

Many herbicides inhibit chloroplast electron transport by interfering with a proteinaceous component of the Qв complex located in the appressed granal membrane. Certain of these herbicides, designated inhibitory uncouplers, also interfere with photophosphorylation and affect other chloroplast-mediated responses, some of which involve components located in the nonappressed granal membrane. The inhibitory uncouplers can be divided into dinoseb (phenolic) types which contain dissociable protons and dicryl (acylanilide) types which are nonionic. The dinoseb types can function as protonophores and shuttle protons across the thylakoid membrane at low concentrations and can alter the integrity of semipermeable membranes at higher concentrations. However, the dicryl types only alter the integrity of the membranes. The inhibitory uncouplers, but not the DCMU-types of electron transport inhibitors: stimulated electron trans- port from DPIPH2 to methyl viologen; inhibited valifiomycin-induced swelling of intact chloroplasts; increased the permeability of the chloroplast envelope to K+ in the absence of an ionophore; prevented energization of the thylakoid membrane by PS I; and increased the permeability of phosphatidyl choline liposomes to protons. Chlorination response patterns obtained with isomers of N-phenyl-2-methylpentanamides in the above reactions, in general, were similar for interference with the Qв complex, i.e., in all assays, dichlorination in the 3,4 or 3,5 positions was associated with maximum inhibitory potency, whereas substitution in an ortho position decreased inhibitory activity. With a series of 1-alkyl-3-(α,α,α-trifluoro-m-tolyl)ureas, maximum inhibition of electron transport was obtained with the butyl derivative, whereas maximum responses for uncoupling and membrane disturbances were obtained with the hexyl or octyl derivatives. Some of the interferences produced by inhibitory uncouplers may result from interactions with the lipoidal components of chloroplast membranes.

Effects of Potassium-(picrate)-(18-crown-6) on the Photosynthetic Electron Transport

1996 ◽  
Vol 51 (7-8) ◽  
pp. 539-547 ◽  
Author(s):  
L. Kovács ◽  
U. Hegde ◽  
S. Padhye ◽  
G. Bernát ◽  
S. Demeter
Keyword(s):  
Electron Transport ◽  
Photosynthetic Electron Transport ◽  
Fluorescence Yield ◽  
Charge Recombination ◽  
Electron Donors ◽  
Low Concentrations ◽  
Tyrosine Z ◽  
High Concentrations ◽  
Tyrosine D ◽  
Potassium Picrate

Abstract The effects of potassium-(picrate)-(18-crown-6) on the electron transport of photosystem II was investigated in isolated pea thylakoids. Low concentrations of the compound inhibited the fast decay of fluorescence yield associated with electron transfer between the primary (QA) and secondary (QB) quinone electron acceptor and increased the intermediary level of fluorescence to the Fmax level. The decay half-time of fluorescence yield measured in the presence of DCMU(S2QA- charge recombination) decreased from about 1.8 s to about 0.3 s in thylakoids treated with potassium-(picrate)-(18-crown-6). While the inhibition of electron transport by DCMU gave rise to the appearance of a thermoluminescence band at about + 10°C (S2QA- charge recombination) addition of potassium-(picrate)-(18-crown-6) resulted in a thermoluminescence band at about -10°C. Increasing concentrations of potassium-(picrate)-(18-crown-6) diminished the fluorescence yield and the -10°C TL band and abolished the Signal IIS and Signal IIf EPR signals of the tyrosine-D and tyrosine-Z electron donors, respectively. The phenolic-type inhibitor, potassium picrate had the same effect on thermoluminescence and on the tyrosine EPR signals. It is concluded that potassium-(picrate)-(18-crown-6) is a phenolic type inhibitor owing to its picrate constituent. At low concentrations picrate and potassium-(picrate)-18-crown) not only block the electron transport between QA and QB but they probably decrease the midpoint redox potential of QA, as well. At high concentrations they also inhibit the light-induced oxidation of the tyrosine-D and tyrosine-Z donors.

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