Quantitative correlation of peripheral and intrinsic core polypeptides of photosystem II with photosynthetic electron-transport activity ofAcetabularia mediterranea in red and blue light

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.

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Effect of Magnesium and Calcium Ions on the Photoelectron Transport Activity of Low-Salt Suspended Hydrilla verticillata Thylakoids: Possible Sites of Cation Interaction

Zeitschrift für Naturforschung C ◽

10.1515/znc-1998-9-1011 ◽

1998 ◽

Vol 53 (9-10) ◽

pp. 849-856

Author(s):

Sujata R. Mishra ◽

Surendra Chandra Sabat

Keyword(s):

Electron Transport ◽

Photosystem Ii ◽

Electron Donor ◽

Water Oxidation ◽

Electron Flow ◽

Hydrilla Verticillata ◽

Transport Activity ◽

Low Salt ◽

Electron Transport Activity ◽

Stimulation Of

Stimulatory effect of divalent cations like calcium (Ca2+) and magnesium (Mg2+) was investigated on electron transport activity of divalent cation deficient low-salt suspended (LS) thylakoid preparation from a submerged aquatic angiosperm, Hydrilla verticillata. Both the cations stimulated electron transport activity of LS-suspended thylakoids having an intact water oxidation complex. But in hydroxylamine (NH2OH) - or alkaline Tris - washed thylakoid preparations (with the water oxidation enzyme impaired), only Ca2+ dependent stimulation of electron transport activity was found. The apparent Km of Ca2+ dependent stimulation of electron flow from H2O (endogenous) or from artificial electron donor (exogenous) to dichlorophenol indophenol (acceptor) was found to be identical. Calcium supported stimulation of electron transport activity in NH2OH - or Tris - washed thylakoids was electron donor selective, i.e., Ca2+ ion was only effective in electron flow with diphenylcarbazide but not with NH2OH as electron donor to photosystem II. A magnesium effect was observed in thylakoids having an intact water oxidation complex and the ion became unacceptable in NH2OH - or Tris - washed thylakoids. Indirect experimental evidences have been presented to suggest that Mg2+ interacts with the water oxidation complex, while the Ca2+ interaction is localized betw een Yz and reaction center of photosystem II.

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Copper Ion Inhibition of Electron Transport Activity in Sodium Chloride Washed Photosystem II Particle Is Partially Prevented by Calcium Ion

Zeitschrift für Naturforschung C ◽

10.1515/znc-1996-3-408 ◽

1996 ◽

Vol 51 (3-4) ◽

pp. 179-184 ◽

Cited By ~ 12

Author(s):

Surendra Chandra Sabat

Keyword(s):

Electron Transport ◽

Photosystem Ii ◽

Calcium Ion ◽

Electron Flow ◽

Copper Ion ◽

Dependent Manner ◽

Transport Activity ◽

Concentration Dependent Manner ◽

Control Activity ◽

Electron Transport Activity

Abstract The inhibitory effects of copper ion (Cu2+) on the photosynthetic electron transport function was investigated both in NaCl washed (depleted in 17 and 23 kDa polypeptides) and native (unwashed) photosystem II membrane preparations from spinach (Beta vulgaris) chlo-roplasts. Copper in the range of 2.0 to 15 μᴍ strongly inhibited the electron flow from water to 2,6-dichlorobenzoquinone in NaCl washed particles in a concentration dependent manner. Com plete inhibition was noticed at 15 μᴍ Cu2+. Oppositely in native membranes, 15 μᴍ C u2+ inhibited only 10-12% of control activity. It was found that calcium ion (Ca2+) significantly reduced the Cu2+ inhibition of electron transport activity. The Ca2+ supported prevention of Cu2+ toxicity was specific to Ca2+. Further analysis indicated that both Cu2+ and Ca2+ act competitively. Since Ca2+ is known to have stimulating/stabilizing effect at the donor side of photosystem II, it is therefore suggested that Cu2+ in NaCl washed particles exerts its inhibitory effect(s) at the oxidizing side of photosystem stimulates/stabilizes the oxygen evolution.

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