Mechanisms of Photosynthetic Oxygen Evolution and Fundamental Hypotheses of Photosynthesis

Zeinalov, Yuzeir

doi:10.1201/9781420027877.sec1

Cited by 10 publications

(11 citation statements)

References 8 publications

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“…2, panel II) The typical oxygen induction curve under continuous illumination exhibits a second order exponential decay kinetics due to the functioning of two mechanisms of oxygen evolution by both types of PSII centers -PSII α and PSII β -that differ in respect to their antenna size as well as in their location in the membranes. PSII β centers, situated mainly in the stroma thylakoids, evolve oxygen by cooperative mechanism, after cooperation of oxygen precursors (positive charges) obtained in different reaction centers, while PSII α centers in grana thylakoids produce oxygen by non-cooperative mechanism (Zeinalov, 1982;Zeinalov, 2005). The contribution of PSII α and PSII β in oxygen evolving process can be estimated by decomposition of oxygen burst decay kinetics into two kinetic components: the fast component being related to the fast PSII α centers and the slow ones -to the slower PSII β .…”

Section: Resultsmentioning

confidence: 99%

Response of isolated thylakoid membranes with altered fluidity to short term heat stress

Velitchkova

Lazarova

Popova

2009

Physiol Mol Biol Plants

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The effect of alterations of lipid phase order of thylakoid membranes on the thermosensitivity of photosystem I (PS I) and photosystem II (PS II) was studied. Plant sterols stigmasterol and cholesterol were applied to decrease the fluidity in isolated membranes. After sterol treatment, a decrease of the temperature of 50 % inhibition of PSII activity was observed. Heat stressinduced stimulation of PSI-mediated electron transport rate was registered for control, but not for sterol-treated membranes. Effect of altered lipid order on oxygen evolving complex was evaluated by means of flash oxygen yields revealing changes in the stoichiometry of PSII α and PSII β centers. The effect of sterol incorporation on the changes in the thermotropic behavior of the main pigment-protein complexes was studied by differential scanning calorimetry (DSC). DSC traces of control thylakoids in the temperature range 20-98 o C exhibited several irreversible endothermic transitions. Incorporation of cholesterol and stigmasterol results in superimposition of the transitions and only two main bands could be resolved. While high temperature band peaks at the same temperature after treatment with both sterols, the band that combines low temperature transitions shows different melting temperature (T m ) : 70 o C for stigmasterol-and 65 0 C for cholesterol-treated membranes. The data presented here emphasise the crucial role of lipid order for the response of thylakoids to high temperatures, mediated not only by changes in the fluidity of bulk lipid phase as result of sterol incorporation but also by changes in the thermotropic properties of pigment-protein complexes.

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Section: Resultsmentioning

confidence: 99%

Response of isolated thylakoid membranes with altered fluidity to short term heat stress

Velitchkova

Lazarova

Popova

2009

Physiol Mol Biol Plants

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“…It is believed that the population of PSII centres, situated mainly in the stroma thylakoids, evolve oxygen by the cooperative mechanism, after cooperation of oxygen precursors (positive charges) obtained in different reaction centres, while PSII α centres produce oxygen by non-cooperative mechanisms. Every reaction centre operates independently from the others and evolves one molecule oxygen after four successive photoreactions (Zeinalov, 2005). The contribution of PSII α and PSII centres to the total amount of oxygen evolved can be estimated by decomposition of the oxygen burst decay curve into two kinetic components.…”

Section: Resultsmentioning

confidence: 99%

“…It has been suggested that the non-cooperative oxygen-evolving mechanism (PSII α centres) operates mainly in grana regions of thylakoid membranes while the cooperative mechanism (PSII centres) takes place predominantly in stroma thylakoids (Maslenkova et al, 1989). It is considered that the centres associated with PSII (situated mainly in the stroma) operate slower than those from the grana-situated (PSII α ) centres (Zeinalov, 2005). The two kinetic components existing at the oxygen burst under continuous illumination reflect the participation of the two different oxygen-evolving mechanisms Ð non-cooperative (Kok's) mechanism realized by PSII α centres and cooperative one connected with PSII (Maslenkova et al, 1989;Zeinalov, 1982Zeinalov, , 2005.…”

Section: Discussionmentioning

confidence: 99%

“…It is considered that the centres associated with PSII (situated mainly in the stroma) operate slower than those from the grana-situated (PSII α ) centres (Zeinalov, 2005). The two kinetic components existing at the oxygen burst under continuous illumination reflect the participation of the two different oxygen-evolving mechanisms Ð non-cooperative (Kok's) mechanism realized by PSII α centres and cooperative one connected with PSII (Maslenkova et al, 1989;Zeinalov, 1982Zeinalov, , 2005. The contribution of the slower (PSII ) component increases after stigmasterol incorporation (Fig.…”

Section: Discussionmentioning

confidence: 99%

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Effect of Membrane Fluidity on Photosynthetic Oxygen Production Reactions

Popova

Velitchkova

Zanev

2007

Zeitschrift Für Naturforschung C

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The effect of changes of membrane fluidity on the oxygen evolving capability of isolated thylakoids was investigated. Alteration of the lipid phase fluidity was achieved by incorporation of the plant sterol stigmasterol. Incorporation of stigmasterol in the lipid bilayer of thylakoid membranes results in rigidization of the hydrophobic phase of thylakoid membranes and decreases the degree of packing of the lipid head groups. These changes of lipid order are accompanied by a reduction of oxygen evolution, measured with 1,4-benzoquinone as an electron acceptor, and by a more pronounced inhibition of PSI-mediated electron transport. By analysis of the parameters of oxygen flash yields and oxygen burst under continuous illumination it was shown that after treatment with stigmasterol: 1.) the number of active oxygen-evolving centres decreased; 2.) the remaining active oxygen-evolving centres were not affected in respect to the oscillation pattern; 3.) the contribution of the slow oxygenevolving centres in oxygen burst yield was increased. The effect of stigmasterol was compared with the well-studied effect of cholesterol. Results were discussed in terms of determining the role of lipid order for the organization and functioning of the photosynthetic machinery.

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“…The investigations of the group are concerned mainly with the luminescence characteristics of the photosynthetic samples-clarification of the mechanisms of the prompt and delayed chlorophyll a fluorescence and the relation between these phenomena (Goltsev and Yordanov 1997;Goltsev et al 2003;2005). For a complete account of the knowledge on prompt fluorescence, see Papageorgiou and Govindjee (2004).…”

Section: Department Of Biophysics and Radiobiology At Sofia Universitymentioning

confidence: 98%

A brief history of the investigations on photosynthesis in Bulgaria

Zeinalov

2006

Photosynth Res

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Investigations on photosynthesis in Bulgaria started in 1941 with the doctoral thesis of Kyrill Popov (University of Münster, Germany). In 1965, at the Institute of Plant Physiology, in Sofia, Kyrill Popov guided the establishment of a special group of researchers on the biochemistry, biophysics and physiology of photosynthesis. In this paper, a brief description of research in photosynthesis in Bulgaria is presented.

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Mechanisms of Photosynthetic Oxygen Evolution and Fundamental Hypotheses of Photosynthesis

Cited by 10 publications

References 8 publications

Response of isolated thylakoid membranes with altered fluidity to short term heat stress

Response of isolated thylakoid membranes with altered fluidity to short term heat stress

Effect of Membrane Fluidity on Photosynthetic Oxygen Production Reactions

A brief history of the investigations on photosynthesis in Bulgaria

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