Photochemical reactions of chlorophyll in dehydrated Photosystem II: two chlorophyll forms (680 and 700 nm)

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.

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Fast enzymatic HCO3- dehydration supports photosynthetic water oxidation in Photosystem II from pea

10.1101/2021.09.30.462629 ◽

2021 ◽

Author(s):

Alexandr V. Shitov ◽

Vasily V. Terentyev ◽

Govindjee Govindjee

Keyword(s):

Photosystem Ii ◽

Pisum Sativum ◽

Water Oxidation ◽

Photochemical Reactions ◽

O2 Evolution ◽

Donor Side ◽

Psii Photochemistry ◽

Similar Dependence ◽

Enzymatic Nature ◽

Photosynthetic Water Oxidation

Carbonic anhydrase (CA) activity, associated with Photosystem II (PSII) from Pisum sativum, has been shown to enhance water oxidation. But, the nature of the CA activity, its origin and role in photochemistry has been under debate, since the rates of CA reactions, measured earlier, were less than the rates of photochemical reactions. Here, we demonstrate high CA activity in PSII from Pisum sativum, measured by HCO3- dehydration at pH 6.5 (i.e. under optimal condition for PSII photochemistry), with kinetic parameters Km of 2.7 mM; Vmax of 2.74·10-2 mM·sec-1; kcat of 1.16·103 sec-1 and kcat/Km of 4.1·105 M-1 sec-1, showing the enzymatic nature of this activity, which kcat exceeds by ~13 times the rate of PSII, as measured by O2 evolution. The similar dependence of HCO3- dehydration, of the maximal quantum yield of photochemical reactions and of O2 evolution on the ratio of chlorophyll/photochemical reaction center II demonstrate the interconnection of these processes on the electron donor side of PSII. Since the removal of protons is critical for fast water oxidation, and since HCO3- dehydration consumes a proton, we suggest that CA activity, catalyzing very fast removal of protons, supports efficient water oxidation in PSII and, thus, photosynthesis in general.

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Effects of Atrazine, Cyanazine, and Procyazine on the Photochemical Reactions of Isolated Chloroplasts

Weed Science ◽

10.1017/s0043174500044064 ◽

1979 ◽

Vol 27 (3) ◽

pp. 300-308 ◽

Cited By ~ 27

Author(s):

P. E. Brewer ◽

C. J. Arntzen ◽

F. W. Slife

Keyword(s):

Electron Transport ◽

Photosystem Ii ◽

Primary Electron ◽

Fluorescence Induction ◽

Photochemical Reactions ◽

Time Dependent ◽

Chlorophyll Fluorescence Induction ◽

Transport Assay ◽

Highly Hydrophobic ◽

Isolated Chloroplasts

The effects of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile}, and procyazine {2-[[4-chloro-6-(cyclopropylamino)-1,3,5-triazine-2-yl] amino]-2-methylpropanenitrile} on the photochemical reactions of isolated pea (Pisum sativum L. ‘Progress #9 Dwarf’) chloroplasts were studied. Atrazine, cyanazine, and procyazine inhibited electron transport but did not uncouple photophosphorylation. The primary site of inhibition for all three herbicides was on the reducing side of photosystem II; the electron transfer step between the primary electron acceptor (Q) and the plastoquinone pool of the electron transport chain is suggested as the site of action of all three herbicides. The amount of inhibition of electron transport observed after addition of herbicide to isolated chloroplasts was time-dependent for cyanazine and procyazine but not for atrazine. This was apparently due to a slower partitioning of cyanazine and procyazine from the aqueous phase of the reaction solution into the highly hydrophobic environment within the chloroplast membrane. Treatment of the thylakoid membranes with detergent reduced the time-dependent inhibitory nature of cyanazine and procyazine, and the ability of atrazine to block electron transport. A photosystem II-dependent electron transport assay and a chlorophyll fluorescence induction assay were used to determine the inhibitory potentials of atrazine, cyanazine, and procyazine. After allowing for differences in the rate of membrane penetration, I50 values of approximately 2 × 10−7 M were determined for each of the three herbicides.

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Photochemical reactions in dehydrated photosynthetic organisms, leaves, chloroplasts and photosystem II particles: reversible reduction of pheophytin and chlorophyll and oxidation of β-carotene

Chemical Physics ◽

10.1016/s0301-0104(03)00277-5 ◽

2003 ◽

Vol 294 (3) ◽

pp. 227-237 ◽

Cited By ~ 21

Author(s):

Vladimir A. Shuvalov ◽

Ulrich Heber

Keyword(s):

Photosystem Ii ◽

Photochemical Reactions ◽

Photosynthetic Organisms ◽

Β Carotene ◽

Reversible Reduction ◽

Photosystem Ii Particles

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Photosynthetic capacity of three phytoplanktonic species measured by a pulse amplitude fluorometric method

Brazilian Journal of Plant Physiology ◽

10.1590/s1677-04202009000300001 ◽

2009 ◽

Vol 21 (3) ◽

pp. 167-174 ◽

Cited By ~ 1

Author(s):

Cleber Cunha Figueredo ◽

Alessandra Giani ◽

José Pires Lemos Filho

Keyword(s):

Electron Transport ◽

Quantum Yield ◽

Photosystem Ii ◽

Photosynthetic Capacity ◽

Electron Transport Rate ◽

Morphological Characteristics ◽

Volume Ratio ◽

Photochemical Reactions ◽

Transport Rate ◽

Photosynthetic Parameters

During photosynthesis, absorbed energy that is not used in photochemical reactions dissipates as fluorescence. Fluorescence provides important information on the physiological conditions of the studied organisms and its measurement is widely used by plant physiologists and can be valuable in phytoplankton studies. We describe a method adapting a plant fluorometric equipment to measure the photosynthetic capacity of microalgae. Unialgal cultures of three planktonic chlorophytes were exposed to 3(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosystem II, at concentrations of 0.1, 1.0 and 10.0 µmol.L-1. Estimates were made of photosynthetic parameters, including operational and potential photosystem II quantum yield and electron transport rate between photosystems, using algal cells concentrated on glass-fiber filters. The technique allowed reliable measurements of fluorescence, and detection of distinct levels of inhibition. Physiological or morphological characteristics of the selected species might provide an explanation for the observed results: differences on the surface/volume ratio of the cells and colony morphology, for example, were associated with contrasting resistance to the toxicant. To characterize inhibition on phytoplanktonic photosynthesis, we suggest operational quantum yield and electron transport rate as best parameters, once they were more sensitive to the DCMU toxicity.

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Photochemical Reactions of Photosystem II in Ethylene Glycol†

Biochemistry ◽

10.1021/bi961724j ◽

1997 ◽

Vol 36 (1) ◽

pp. 76-85 ◽

Cited By ~ 6

Author(s):

Warwick Hillier ◽

Philip Lukins ◽

Michael Seibert ◽

Tom Wydrzynski

Keyword(s):

Photosystem Ii ◽

Ethylene Glycol ◽

Photochemical Reactions

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Effect of Photosystem II inhibitor K-15 on photochemical reactions of the isolated D1/D2 cytochrome b559 complex

Photosynthesis Research ◽

10.1007/bf00018297 ◽

1995 ◽

Vol 44 (1-2) ◽

pp. 67-74 ◽

Cited By ~ 10

Author(s):

Vyacheslav V. Klimov ◽

Sergei K. Zharmukhamedov ◽

Javier De Las Rivas ◽

James Barber

Keyword(s):

Photosystem Ii ◽

Photochemical Reactions ◽

Cytochrome B559

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Photosynthetic Electron Transport Inhibition by Buthidazole

Weed Science ◽

10.1017/s0043174500025832 ◽

1981 ◽

Vol 29 (1) ◽

pp. 59-64 ◽

Cited By ~ 7

Author(s):

A. C. York ◽

C. J. Arntzen ◽

F. W. Slife

Keyword(s):

Electron Transport ◽

Photosystem Ii ◽

Photosynthetic Electron Transport ◽

Photochemical Reactions ◽

Secondary Site ◽

Major Site ◽

Photosynthetic Electron Transport Chain ◽

Transport Inhibition ◽

Transport Chain ◽

Transfer Inhibitor

The effects of buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} on the photochemical reactions of isolated pea (Pisum sativumL.) chloroplast thylakoids were analyzed. Buthidazole was found to inhibit electron transport at two distinct sites in the photosynthetic electron transport chain. The major site of inhibition was on the reducing side of photosystem II at the site of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] inhibition. Buthidazole also had a secondary site of electron transport inhibition on the oxidizing side of photosystem II. No evidence was found for buthidazole to act as an uncoupler or as an energy transfer inhibitor.

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Long-term stress induced by nitrate deficiency, sodium chloride, and high light on photosystem II activity and carotenogenesis of green alga Scenedesmus sp.

Botany ◽

10.1139/b2012-077 ◽

2012 ◽

Vol 90 (10) ◽

pp. 1007-1014 ◽

Cited By ~ 3

Author(s):

Laura Pirastru ◽

François Perreault ◽

Fong Lam Chu ◽

Abdallah Oukarroum ◽

Lekha Sleno ◽

...

Keyword(s):

Sodium Chloride ◽

Photosystem Ii ◽

Green Alga ◽

Physiological Stress ◽

Photochemical Efficiency ◽

Photochemical Reactions ◽

High Light ◽

Long Term Study ◽

Secondary Carotenoids

The green alga Scenedesmus sp. was exposed to a long-term physiological stress of 40 days induced by the combination of nitrate deficiency, different concentrations of sodium chloride, and high light irradiance. Under these conditions, the change of photosystem II (PSII) photochemical reactions of photosynthesis and cellular growth were investigated along with the synthesis of secondary carotenoids, including astaxanthin and canthaxanthin. From 10 to 40 days, the biosynthesis of these secondary carotenoids was highly induced after the deterioration of PSII complexes when chlorophyll synthesis and cell division were inhibited. In this long term study, the highest induction of carotenoid synthesis happened after the deterioration of PSII reaction centers. There was no direct relationship between the induction of secondary carotenoids and the decline of PSII photochemical efficiency, although it may contribute to carotenogenesis. Under this stressful condition, viability of cells was noted by the small change of unbleached cell density compared with control after 40 days. Therefore, Scenedesmus sp. was tolerant to the long-term chronic stress condition caused by the production of secondary carotenoids, such as astaxanthin and cantaxanthin, participating in antioxidative mechanisms to protect algal cellular system.

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Characterization of photosystem II with the atomic-force microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100130365 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1146-1147

Author(s):

Kathleen M. Marr ◽

Mary K. Lyon

Keyword(s):

Photosystem Ii ◽

Atomic Force Microscope ◽

Three Dimensional ◽

Biologically Active ◽

Atomic Force ◽

Freeze Etching ◽

Image Averaging ◽

Oxygen Evolving ◽

Averaging Techniques

Photosystem II (PSII) is different from all other reaction centers in that it splits water to evolve oxygen and hydrogen ions. This unique ability to evolve oxygen is partly due to three oxygen evolving polypeptides (OEPs) associated with the PSII complex. Freeze etching on grana derived insideout membranes revealed that the OEPs contribute to the observed tetrameric nature of the PSIl particle; when the OEPs are removed, a distinct dimer emerges. Thus, the surface of the PSII complex changes dramatically upon removal of these polypeptides. The atomic force microscope (AFM) is ideal for examining surface topography. The instrument provides a topographical view of individual PSII complexes, giving relatively high resolution three-dimensional information without image averaging techniques. In addition, the use of a fluid cell allows a biologically active sample to be maintained under fully hydrated and physiologically buffered conditions. The OEPs associated with PSII may be sequentially removed, thereby changing the surface of the complex by one polypeptide at a time.

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