Trimeric organization of photosystem I is required to maintain the balanced photosynthetic electron flow in cyanobacterium Synechocystis sp. PCC 6803.

In Synechocystis sp. PCC 6803 and some other cyanobacteria photosystem I reaction centres exist predominantly as trimers, with minor contribution of monomeric form, when cultivated at standard optimized conditions. In contrast, in plant chloroplasts photosystem I complex is exclusively monomeric.

Photosystem I oligomerization affects lipid composition in Synechocystis sp. PCC 6803.

In cyanobacteria, increasing growth temperature decreases lipid unsaturation and the ratio of monomer/trimer photosystem I (PSI) complexes. In the present study we applied Fourier-transform infrared (FTIR) spectroscopy and lipidomic analysis to study the effects of PSI monomer/oligomer ratio on the physical properties and lipid composition of thylakoids. To enhance the presence of monomeric PSI, a Synechocystis sp.

Opposite domination of cyclic and pseudocyclic electron flows in short-illuminated dark-adapted leaves of angiosperms and gymnosperms.

The present work was aimed to explain the recently reported higher O-dependent electron flow capacity in gymnosperms than in angiosperms and to search for other differences in the electron transport processes by simultaneous characterization of the relative capacities of pseudocyclic (direct or Flavodiiron proteins (Flv)-mediated O-reduction, Mehler(-like) reactions) and cyclic electron flows around photosystem I (CEF-PSI). To this end, a comparative multicomponent analysis was performed on the fluorescence decay curves of dark-adapted leaves after illumination with a 1-s saturating light pulse. In both gymnosperms and angiosperms, two or three exponential decay components were resolved: fast (t 1 ~ 170-260 ms), middle (~1.

Chlorophyll a is the crucial redox sensor and transmembrane signal transmitter in the cytochrome b6f complex. Components and mechanisms of state transitions from the hydrophobic mismatch viewpoint.

The cytochrome (cyt) b6f complex is involved in the transmembrane redox signaling that triggers state transitions in cyanobacteria and chloroplasts. However, the components and molecular mechanisms are still unclear. In an attempt to solve this long-standing problem, we first focused on the unknown role of a single chlorophyll a (Chla) in cyt b6f with a new approach based on Chla structural properties.

Action and target sites of nitric oxide in chloroplasts.

Nitric oxide (NO) is an important signalling molecule in plants under physiological and stress conditions. Here we review the influence of NO on chloroplasts which can be directly induced by interaction with the photosynthetic apparatus by influencing photophosphorylation, electron transport activity and oxido-reduction state of the Mn clusters of the oxygen-evolving complex or by changes in gene expression. The influence of NO-induced changes in the photosynthetic apparatus on its functions and sensitivity to stress factors are discussed.

Effects of exogenous 24-epibrassinolide on the photosynthetic membranes under non-stress conditions.

In the present work the effects of exogenous 24-epibrassinolide (EBR) on functional and structural characteristics of the thylakoid membranes under non-stress conditions were evaluated 48 h after spraying of pea plants with different concentrations of EBR (0.01, 0.1 and 1.

Photoelectron transport ability of chloroplast thylakoid membranes treated with NO donor SNP: changes in flash oxygen evolution and chlorophyll fluorescence.

The nitric oxide (NO) donor sodium nitroprusside (SNP) is frequently used in plant science in vivo. The present in vitro study reveals its effects on the photosynthetic oxygen evolution and the chlorophyll fluorescence directly on isolated pea thylakoid membranes. It was found that even at very low amounts of SNP (chlorophyll/SNP molar ratio∼67:1), the SNP-donated NO stimulates with more than 50% the overall photosystem II electron transport rate and diminishes the evolution of molecular oxygen.

Bilayer structural destabilization by low amounts of chlorophyll a.

The present study shows that small admixtures of one chlorophyll a (Chla) molecule per several hundred lipid molecules have strong destabilizing effect on lipid bilayers. This effect is clearly displayed in the properties of the L(alpha)-H(II) transformations and results from a Chla preference for the H(II) relative to the L(alpha) phase. Chla disfavors the lamellar liquid crystalline phase L(alpha) and induces its replacement with inverted hexagonal phase H(II), as is consistently demonstrated by DSC and X-ray diffraction measurements on phosphatidylethanolamine (PE) dispersions.