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2. Alternative cyanide-sensitive oxidase interacting with photosynthesis in synechocystis PCC6803. Ancestor of the terminal oxidase of chlororespiration?

Creator:
Büchel, C., Zsíros, O., and Garab, G.
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
absorbance, azide, cyanobacteria, cytochromes, flash radiation, KCN, NaN3, phylogeny, respiration, and salicyl hydroxamic acid
Language:
Multiple languages
Description:
Influence of respiration on photosynthesis in Synechocystis PCC6803 was studied by measuring the redox transients of cytochrome f (cyt f) upon excitation of the cells with repetitive single turnover flashes. Upon the addition of KCN the flash-induced oxidation of cyt f was increased and the rereduction of cyt f+ was accelerated. Dependence of these effects on the concentration of KCN clearly demonstrated the existence of two cyanide-sensitive oxidases interacting with photosynthesis: cyt aa3, which was sensitive to low concentrations of cyanide, and an alternative oxidase, which could be suppressed by using ≥1 mM KCN. The interaction between the photosynthetic and the respiratory electron transport chains was regulated mainly by the activity of the alternative cyanide-sensitive oxidase. The oxidative pathway involving the alternative cyanide-sensitive oxidase was insensitive to salicyl hydroxamic acid and azide. The close resemblance of the inhibition pattern reported here and that described for chlororespiration in algae and higher plants strongly suggest that an oxidase of the same type as the alternative cyanide-sensitive oxidase of cyanobacteria functions as a terminal oxidase in chloroplasts. and C. Büchel, O. Zsíros, G. Garab.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

3. Dependence of the rate-limiting steps in the dark-to-light transition of photosystem II on the lipidic environment of the reaction center

Creator:
Magyar, M., Akhtar, P., Sipka, G., Han, W., Li, X., Han, G., Shen, J.-R., Lambrev, P. H., and Garab, G.
Format:
počítač and online zdroj
Type:
model:article and TEXT
Subject:
losed state of PSII, conformational changes, dielectric relaxation, light-adapted state of PSII, light-induced changes, and proteoliposomes
Language:
Multiple languages
Description:
In our earlier works, we have identified rate-limiting steps in the dark-to-light transition of PSII. By measuring chlorophyll a fluorescence transients elicited by single-turnover saturating flashes (STSFs) we have shown that in diuron-treated samples an STSF generates only F1 (< Fm) fluorescence level, and to produce the maximum (Fm) level, additional excitations are required, which, however, can only be effective if sufficiently long Δτ waiting times are allowed between the excitations. Biological variations in the half-rise time (Δτ1/2) of the fluorescence increment suggest that it may be sensitive to the physicochemical environment of PSII. Here, we investigated the influence of the lipidic environment on Δτ1/2 of PSII core complexes of Thermosynechococcus vulcanus. We found that while non-native lipids had no noticeable effects, thylakoid membrane lipids considerably shortened the Δτ1/2, from ~ 1 ms to ~ 0.2 ms. The importance of the presence of native lipids was confirmed by obtaining similarly short Δτ1/2 values in the whole T. vulcanus cells and isolated pea thylakoid membranes. Minor, lipid-dependent reorganizations were also observed by steady-state and time-resolved spectroscopic measurements. These data show that the processes beyond the dark-to-light transition of PSII depend significantly on the lipid matrix of the reaction center.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

4. Effect of chromium on photosystem 2 in the unicellular green alga, Chlorella pyrenoidosa

Creator:
Hörcsik, Z. T., Kovács, L., Láposi, R., Mészáros, I., Lakatos, G., and Garab, G.
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
chlorophyll fluorescence, D1 protein, Western blot analysis, and thermoluminescence
Language:
Multiple languages
Description:
We investigated the effect of chromium (20-40 g m-3, 8-72 h) on the photosystem 2 (PS2) activities of Chlorella pyrenoidosa cells. By using chlorophyll fluorescence transients, thermoluminescence, oxygen polarography, and Western blot analysis for D1 protein we found that inhibition of PS2 can be accounted for by the enhanced photodestruction of the reaction centres in the cells cultivated in the presence of Cr(VI) at 25 °C in "white light" (18 W m-2). Hence photodestruction of D1 is caused by an enhanced oxidative stress and lipid peroxidation, as indicated by the appearance of a high-temperature thermoluminescence band. and Z. T. Hörcsik ... [et al.].
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

5. Increased thermal stability of photosystem II and the macro-organization of thylakoid membranes, induced by co-solutes, associated with changes in the lipid-phase behaviour of thylakoid membranes

Creator:
Kotakis, C., Akhtar, P., Zsiros, O., Garab, G., and Lambrev, P. H.
Format:
print, bez média, and svazek
Type:
model:article and TEXT
Subject:
fotosyntéza, photosynthesis, circular dichroism, merocyanine-540, non-bilayer lipids, osmolyte, time-resolved fluorescence spectroscopy, 2, and 581
Language:
Multiple languages
Description:
The principal function of the thylakoid membrane depends on the integrity of the lipid bilayer, yet almost half of the thylakoid lipids are of non-bilayer-forming type, whose exact functions are not fully understood. Non-bilayer lipids can be extruded from the membrane in the presence of high concentrations of co-solutes. We applied 2 M sucrose to induce lipid phase separation in isolated thylakoid membranes, following consequent structural and physiological effects. Circular dichroism spectroscopy indicated significant changes in the chiral macro-arrangement of the pigment-protein complexes, which were reversed after washing out the co-solute. Similarly, merocyanine-540 fluorescence suggested reversible changes in the lipid phases. The PSII function, as tested by chlorophyll fluorescence induction transients and time-resolved fluorescence, was almost unaffected. However, the presence of sucrose dramatically increased the PSII thermostability, which can partly be explained by a direct osmolyte effect and partly by the lipid phase separation stabilizing the stacked membrane., C. Kotakis, P. Akhtar, O. Zsiros, G. Garab, P. H. Lambrev., and Obsahuje bibliografické odkazy
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

6. Tribute to Jean Lavorel (1928-2021), an outstanding experimenter and a brilliant theorist of photosynthesis

Creator:
Govindjee, G., De Kouchkovsky, Y., and Garab, G.
Format:
počítač and online zdroj
Type:
model:article and TEXT
Subject:
Jean Lavorel
Language:
Multiple languages
Description:
Tribute to Jean Lavorel (16 March 1928–12 January 2021), a pioneer of the ‘Light Reactions of Photosynthesis’. He was known not only for his ingenuity in devising new instruments but in thoroughly analyzing all the available data theoretically and mathematically – mostly all by himself. He measured, elegantly, oxygen evolution and light given off by photosynthetic organisms, both prompt and delayed chlorophyll fluorescence. He ingeniously used these data to understand how light energy is converted to chemical energy in natural systems. We present below a summary of his life and research.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public