Effect of red light on photosynthetic acclimation and the gene expression of certain light signalling components involved in the microRNA biogenesis in the extremophile Eutrema salsugineum.

The photosynthetic acclimation of extremophile Eutrema salsugineum plants to red light (RL) (14 days, 150 µmol photons m-2 s-1, 660 nm) and the expression of the key photoreceptor apoprotein genes, transcription factors (TFs) and associated with phytochrome system MIR (microRNA) genes were studied. RL exposure induced an increase in the content of anthocyanin and total phenolic compounds and the level of Chls was decreased. The photosystem 2 electron transport rate and the number of open reaction centres (qL) were not changed in RL plants, however, the levels of non-photochemical quenching (NPQ) and the regulated quantum yield of non-photochemical quenching Y(NPQ) were significantly higher in the RL plants. The rate of CO2 uptake was decreased by almost 1.4-fold but the respiration and transpiration rates, as well as the stomatal conductance were not changed in the RL plants. An increase in the expression of the photoreceptor apoprotein genes PHYA, PHYB and PHYC, the TF genes PIF4, PIF5 and miR395, miR408, miR165 and decreases in the levels of the transcripts of the TF gene HY5 and miR171, miR157, and miR827 were detected. The acclimation effect of photosynthetic apparatus to RL was accompanied by an increase of pigment content such as total phenolic compounds and carotenoids and it is due to the changes in the expression of the apoprotein phytochrome genes PHYA, PHYB, PHYC and phytochrome signalling TFs (PIF4, PIF5 and HY5) as well as MIR genes associated with phytochrome system.

Mechanisms of inhibitory effects of polycyclic aromatic hydrocarbons in photosynthetic primary processes in pea leaves and thylakoid preparations.

Inhibitory effects of polycyclic aromatic hydrocarbons (PAHs) on plants were studied in pea leaves in order to elucidate the mechanisms of action of PAHs such as naphthalene (Naph) and phenanthrene (Phen) on activity of photosystem II (PSII). The changes in different Chl fluorescence parameters were calculated on the basis of Chl fluorescence induction curves. H2 O2 content was measured in leaf homogenates with the luminol-dependent chemiluminescence method. We demonstrated that following PAH treatment, total energy dissipation (DI0 /ABS) and amount of QB -non-reducing complexes of PSII significantly increased. Non-photochemical quenching (NPQ) also increased, when weak oxidative stress after PAH application developed. In leaves, a two-step increase in H2 O2 was found with time of incubation in the presence of PAHs, which may be associated with damage to the lipid bilayer of the plasma membrane and then violation of lipid bilayer membranes of cell organelles. A hypothesis for the mode of action of PAHs is provided that involves the role of ROS, membrane permeability and associated functional changes in PSII.

Chlorophylls d and f and Their Role in Primary Photosynthetic Processes of Cyanobacteria.

The finding of unique Chl d- and Chl f-containing cyanobacteria in the last decade was a discovery in the area of biology of oxygenic photosynthetic organisms. Chl b, Chl c, and Chl f are considered to be accessory pigments found in antennae systems of photosynthetic organisms. They absorb energy and transfer it to the photosynthetic reaction center (RC), but do not participate in electron transport by the photosynthetic electron transport chain. However, Chl d as well as Chl a can operate not only in the light-harvesting complex, but also in the photosynthetic RC. The long-wavelength (Qy) Chl d and Chl f absorption band is shifted to longer wavelength (to 750 nm) compared to Chl a, which suggests the possibility for oxygenic photosynthesis in this spectral range. Such expansion of the photosynthetically active light range is important for the survival of cyanobacteria when the intensity of light not exceeding 700 nm is attenuated due to absorption by Chl a and other pigments. At the same time, energy storage efficiency in photosystem 2 for cyanobacteria containing Chl d and Chl f is not lower than that of cyanobacteria containing Chl a. Despite great interest in these unique chlorophylls, many questions related to functioning of such pigments in primary photosynthetic processes are still not elucidated. This review describes the latest advances in the field of Chl d and Chl f research and their role in primary photosynthetic processes of cyanobacteria.

Photoinhibition of photosystem I in a pea mutant with altered LHCII organization.

Comparative analysis of in vivo chlorophyll fluorescence imaging revealed that photosystem II (PSII) photochemical efficiency (Fv/Fm) of leaves of the Costata 2/133 pea mutant with altered pigment composition and decreased level of oligomerization of the light harvesting chlorophyll a/b-protein complexes (LHCII) of PSII (Dobrikova et al., 2000; Ivanov et al., 2005) did not differ from that of WT. In contrast, photosystem I (PSI) activity of the Costata 2/133 mutant measured by the far-red (FR) light inducible P700 (P700(+)) signal exhibited 39% lower steady state level of P700(+), a 2.2-fold higher intersystem electron pool size (e(-)/P700) and higher rate of P700(+) re-reduction, which indicate an increased capacity for PSI cyclic electron transfer (CET) in the Costata 2/133 mutant than WT. The mutant also exhibited a limited capacity for state transitions. The lower level of oxidizable P700 (P700(+)) is consistent with a lower amount of PSI related chlorophyll protein complexes and lower abundance of the PsaA/PsaB heterodimer, PsaD and Lhca1 polypeptides in Costata 2/133 mutant. Exposure of WT and the Costata 2/133 mutant to high light stress resulted in a comparable photoinhibition of PSII measured in vivo, although the decrease of Fv/Fm was modestly higher in the mutant plants. However, under the same photoinhibitory conditions PSI photochemistry (P700(+)) measured as ΔA820-860 was inhibited to a greater extent (50%) in the Costata 2/133 mutant than in the WT (22%). This was accompanied by a 50% faster re-reduction rate of P700(+) in the dark indicating a higher capacity for CET around PSI in high light treated mutant leaves. The role of chloroplast thylakoid organization on the stability of the PSI complex and its susceptibility to high light stress is discussed.

Photobiological hydrogen production and artificial photosynthesis for clean energy: from bio to nanotechnologies.

Global energy demand is increasing rapidly and due to intensive consumption of different forms of fuels, there are increasing concerns over the reduction in readily available conventional energy resources. Because of the deleterious atmospheric effects of fossil fuels and the uncertainties of future energy supplies, there is a surge of interest to find environmentally friendly alternative energy sources. Hydrogen (H2) has attracted worldwide attention as a secondary energy carrier, since it is the lightest carbon-neutral fuel rich in energy per unit mass and easy to store. Several methods and technologies have been developed for H2 production, but none of them are able to replace the traditional combustion fuel used in automobiles so far. Extensively modified and renovated methods and technologies are required to introduce H2 as an alternative efficient, clean, and cost-effective future fuel. Among several emerging renewable energy technologies, photobiological H2 production by oxygenic photosynthetic microbes such as green algae and cyanobacteria or by artificial photosynthesis has attracted significant interest. In this short review, we summarize the recent progress and challenges in H2-based energy production by means of biological and artificial photosynthesis routes.

Effect of naphthalene on photosystem 2 photochemical activity of pea plants.

The effect of a typical polyaromatic hydrocarbon, naphthalene (Naph), on photosystem 2 (PS-2) photochemical activity in thylakoid membrane preparations and 20-day-old pea leaves was studied. Samples were incubated in water in the presence of Naph (0.078, 0.21, and 0.78 mM) for 0.5-24 h under white light illumination (15 µmol photons·m(-2)·s(-1)). The PS-2 activity was determined by studying fast and delayed chlorophyll (Chl) a fluorescence. Incubation of samples in water solutions at Naph concentrations of 0.21 and 0.78 mM led to a decrease in the maximum PS-2 quantum efficiency (Fv/Fm), noticeable changes in the polyphasic induction kinetics of fluorescence (OJIP), and a decrease in the amplitudes of the fast and slow components of delayed fluorescence of Chl a. The rate of release of electrolytes from leaves that were preliminarily incubated with Naph (0.21 mM) was also increased. Significant decrease in the fluorescence parameters in thylakoid membrane preparations was observed at Naph concentration of 0.03 mM and 12-min exposure of the samples. Chlorophyll (a and b) and carotenoid content (mg per gram wet mass) was insignificantly changed. The quantum yields of electron transfer from QA to QB (φET2o) and also to the PS-1 acceptors (φRE1o) were reduced. These results are explained by the increase in the number of QB-non-reducing centers of PS-2, which increased with increasing Naph concentration and exposure time of leaves in Naph solution. The suppression of PS-2 activity was partly abolished in the presence of the electron donor sodium ascorbate. Based on these results, it is suggested that Naph distorts cell membrane intactness and acts mainly on the PS-2 acceptor and to a lesser degree on the PS-2 donor side.

Nano-sized manganese-calcium cluster in photosystem II.

Cyanobacteria, algae, and plants are the manufacturers that release O2 via water oxidation during photosynthesis. Since fossil resources are running out, researchers are now actively trying to use the natural catalytic center of water oxidation found in the photosystem II (PS II) reaction center of oxygenic photosynthetic organisms to synthesize a biomimetic supercatalyst for water oxidation. Success in this area of research will transcend the current bottleneck for the development of energy-conversion schemes based on sunlight. In this review, we go over the structure and function of the water-oxidizing complex (WOC) found in Nature by focusing on the recent advances made by the international research community dedicated to achieve the goal of artificial water splitting based on the WOC of PS II.

Bicarbonate stimulates the electron donation from Mn²âº to P680⁺ in isolated D1/D2/cytochrome b559 complex.

Influence of bicarbonate on the efficiency of the electron donation from Mn(2+) to P680(+) in isolated D1/D2/cytochrome b559 complex was investigated. All the experiments were carried out in a medium depleted of HCO3(-)/CO2. Kinetics of photoinduced absorbance changes (ΔA) at different wavelengths and decrease of chlorophyll fluorescence yield (-ΔF) related to photoaccumulation of reduced pheophytin, the intermediary electron acceptor of photosystem II (PSII), in the presence of Mn(2+) under anaerobic conditions were measured. Addition of bicarbonate (1 mM) increased the amplitude of these ΔA and -ΔF at least by a factor of 3. Measurements of the photoinduced ΔA, related to photooxidation of the primary electron donor of PSII, chlorophyll P680, were done in the presence of silicomolybdate as electron acceptor. These results show that the addition of 0.05 mM Mn(2+) alone or jointly with 1 mM bicarbonate induces a 20% and 70%-decrease of the magnitude of the ΔA at 680 nm. The effect of Mn(2+) (in the presence and absence of bicarbonate) was completely eliminated by the addition of 12 mM EDTA. All these bicarbonate effects were not observed if MgCl2 or formate were used instead of MnCl2 and bicarbonate, respectively. In the absence of Mn(2+), bicarbonate induced none of the mentioned above effects (increase of photoaccumulation of reduced pheophytin and decrease of photooxidation of P680). The presented data suggest that bicarbonate stimulates the electron donation from Mn(2+) to D1/D2/cyt b559 reaction center evidently due to formation of easily oxidizable Mn-bicarbonate complexes.

Identification and differential expression of two dehydrin cDNAs during maturation of Jatropha curcas seeds.

Plant dehydrin proteins (DHNs) are known to be important for environmental stress tolerance and are involved in various developmental processes. Two full-length cDNAs JcDHN-1 and JcDHN-2 encoding two dehydrins from Jatropha curcas seeds were identified and characterized. JcDHN-1 is 764 bp long and contains an open reading frame of 528 bp. The deduced JcDHN-1 protein has 175 a.a. residues that form a 19.3-kDa polypeptide with a predicted isoelectric point (pI) of 6.41. JcDHN-2 is 855 bp long and contains an open reading frame of 441 bp. The deduced JcDHN-2 protein has 156 a.a. residues that form a 17.1-kDa polypeptide with a predicted pI of 7.09. JcDHN-1 is classified as type Y3SK2 and JcDHN-2 is classified as type Y2SK2 according to the YSK shorthand for structural classification of dehydrins. Homology analysis indicates that both JcDHN-1 and JcDHN-2 share identity with DHNs of other plants. Analysis of the conserved domain revealed that JcDHN-2 has glycoside hydrolase GH20 super-family activity. Quantitative real time PCR analysis for JcDHN-1 and JcDHN-2 expression during seed development showed increasing gene expression of both their transcript levels along with the natural dehydration process during seed development. A sharp increase in JcDHN-2 transcript level occurred in response to water content dropping from 42% in mature seeds to 12% in dry seeds. These results indicate that both JcDHNs have the potential to play a role in cell protection during dehydration occurring naturally during jatropha orthodox seed development.

Genetic decrease in fatty acid unsaturation of phosphatidylglycerol increased photoinhibition of photosystem I at low temperature in tobacco leaves.

Leaves of transgenic tobacco plants with decreased levels of fatty acid unsaturation in phosphatidylglycerol (PG) exhibited a slightly lower level of the steady state oxidation of the photosystem I (PSI) reaction center P700 (P700(+)) than wild-type plants. The PSI photochemistry of wild-type plants was only marginally affected by high light treatments. Surprisingly, all plants of transgenic lines exhibited much higher susceptibility to photoinhibition of PSI than wild-type plants. This was accompanied by a 2.5-fold faster re-reduction rate of P700(+) in the dark, indicating a higher capacity for cyclic electron flow around PSI in high light treated transgenic leaves. This was associated with a much higher intersystem electron pool size suggesting over-reduction of the PQ pool in tobacco transgenic lines with altered PG unsaturation compared to wild-type plants. The physiological role of PG unsaturation in PSI down-regulation and modulation of the capacity of PSI-dependent cyclic electron flows and distribution of excitation light energy in tobacco plants under photoinhibitory conditions at low temperatures is discussed. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

A carbonic anhydrase inhibitor induces bicarbonate-reversible suppression of electron transfer in pea photosystem 2 membrane fragments.

The effects of suppression of the carbonic anhydrase (CA) activity by a CA-inhibitor, acetazolamide (AA), on the photosynthetic activities of photosystem II (PS II) particles from higher plants were investigated. AA along with CA-activity inhibits the PS II photosynthetic electron transfer and the AA-induced suppression is totally reversed by the addition of bicarbonate (3-5 mM). Similar effect of recovery in the PS II photosynthetic activity was also revealed upon the addition of known artificial electron donors (potassium ferrocyanide and TMPD). Significance and possible functions of CA for the PS II donor side are discussed.

High salt stress in coupled and uncoupled thylakoid membranes: a comparative study.

The effect of high salt concentration on photosystem II (PS II) electron transport rates and chlorophyll a fluorescence induction kinetics was investigated in coupled and uncoupled spinach thylakoid membranes. With increase in salt concentration, the rates of electron transport mediated by PS II and the F(v)/F(m) ratio were affected more in uncoupled thylakoids as compared to coupled thylakoid membranes. The uncoupled thylakoid membranes seemed to behave like coupled thylakoid membranes at high NaCl concentration (approximately 1 M). On increasing the salt concentration, the uncoupler was found to be less effective and Na+ probably worked as a coupling enhancer or uncoupling suppressor. We suggest that positive charge of Na+ mimics the function of positive charge of H+ in the thylakoid lumen in causing coupled state. The function of NaCl (monovalent cation) could be carried out by even lower concentration of Ca2+ (divalent cation) or Al3+ (trivalent cation). We conclude that this function of NaCl as coupling enhancer is not specific, and in general a positive charge is required for causing coupling in uncoupled thylakoid membranes.

Manganese-dependent carboanhydrase activity of photosystem II proteins.

Four sources of carbonic anhydrase (CA) activity in submembrane preparations of photosystem II (PS II) isolated from pea leaves were examined. Three of them belong to the hydrophilic proteins of the oxygen-evolving complex of PS II with molecular mass 33 kDa (protein PsbO), 24 kDa (protein PsbP), and 18 kDa (protein PsbQ). The fourth source of CA activity is associated with a pigment-protein complex of PS II after removing three hydrophilic proteins by salt treatment. Except for protein PsbQ, the CA activity of all these proteins depends on the presence of Mn2+: the purified protein PsbO did not show CA activity before adding Mn2+ into the medium (concentration of Mn2+ required for 50% effect, EC(50), was 670 microM); CA activity of protein mixture composed of PsbP and PsbQ increased more than 5-fold upon adding Mn2+ (EC(50) was 45 microM). CA activity of purified protein PsbP increased 2-fold in the presence of 200 microM Mn2+. As indicated for the mixture of two proteins (PsbP and PsbQ), Mg2+, Ca2+, and Zn2+, in contrast to Mn2+, suppressed CA activity (both initial and Mn2+-induced activity). Since the found sources of CA activity demonstrated properties different from ones of typical CA (need for Mn2+, insensitivity or low sensitivity to acetazolamide or ethoxyzolamide) and such CA activity was found only among PS II proteins, we cannot exclude that they belong to the type of Mn-dependent CA associated with PS II.

Binding of novel inhibitors of electron transfer in photosystem 2, derivatives of perfluoroisopropyldinitrobenzene, with polypeptide D2 of the reaction center.

A binding site for novel inhibitors of K15 type (derivatives of perfluoroisopropyldinitrobenzene) with the components of reaction center (RC) of photosystem 2 (PS-2) of higher plants has been investigated. It has been shown that multiple washing the PS-2 submembrane chloroplast fragments (BBY-particles) treated with the K15 inhibitor, including multiple dilution in buffer in the presence of high concentrations of mono- and divalent ions, prolonged (up to 2-5 h) incubation, centrifugation, and subsequent resuspension in buffer deprived of the inhibitor, does not lead to restoration of functional activity of the PS-2. After addition of dithionite, inducing reduction and consequent decomposition of the inhibitor, and subsequent removal of dithionite by washing, the functional activity of PS-2 was completely restored. Incubation in the presence of sodium dodecyl sulfate (SDS), leading to solubilization of the sample to the level of protein components, induced the appearance of a fraction of free K15 retaining the initial inhibitory efficiency. To create a covalent binding of the inhibitor with protein, retained under the conditions of denaturing SDS polyacrylamide gel electrophoresis, the azido-containing analog of K15 (K15-N(3)) was used. The need for radioactive label for identification of K15 was avoided by the revealed ability of K15-type inhibitors to emit fluorescence, which retained its features under the experimental conditions. With the technique of photoaffinity binding and denaturing SDS-PAGE in the presence of 6 M urea of submembrane chloroplast fragments enriched in PS-2 the D2-polypeptide, an integral component of the reaction center of PS-2, has been shown to be a binding site for K15-type inhibitors. This conclusion is in agreement with a suggestion (put forward in our earlier publications) that K15-type inhibitors are bound to PS-2 reaction center, replacing Q(A) in its binding site. Hence, an agent specifically binding to polypeptide D2 has been found for the first time. The data are compared with information about inhibitory action and binding sites of the known inhibitors of electron transfer in PS-2.

Oxidative stress inhibits the repair of photodamage to the photosynthetic machinery.

Absorption of excess light energy by the photosynthetic machinery results in the generation of reactive oxygen species (ROS), such as H2O2. We investigated the effects in vivo of ROS to clarify the nature of the damage caused by such excess light energy to the photosynthetic machinery in the cyanobacterium Synechocystis sp. PCC 6803. Treatments of cyanobacterial cells that supposedly increased intracellular concentrations of ROS apparently stimulated the photodamage to photosystem II by inhibiting the repair of the damage to photosystem II and not by accelerating the photodamage directly. This conclusion was confirmed by the effects of the mutation of genes for H2O2-scavenging enzymes on the recovery of photosystem II. Pulse labeling experiments revealed that ROS inhibited the synthesis of proteins de novo. In particular, ROS inhibited synthesis of the D1 protein, a component of the reaction center of photosystem II. Northern and western blot analyses suggested that ROS might influence the outcome of photodamage primarily via inhibition of translation of the psbA gene, which encodes the precursor to D1 protein.

Optical study of cytochrome cM formation in Synechocystis.

The expression of the cytM gene, which encodes cytochrome cM in Synechocystis sp. PCC 6803, is induced under stress conditions such as low temperature. Results of spectrophotometric studies revealed that cytochrome cM was oxidized by light absorbed by photosystem I in cells that had acclimatized to a low temperature. However, no similar light-induced oxidation of cytochrome cM was observed in delta cytM mutant cells. The kinetics of the oxidation and reduction of P700 before and after acclimation of Synechocystis cells to low temperature suggested that cytochrome cM might donate electrons to photooxidized P700. Our observations indicate that cytochrome cM is synthesized under low-temperature stress and that it might carry electrons directly to P700+ in photosystem I.

Unsaturated fatty acids in membrane lipids protect the photosynthetic machinery against salt-induced damage in Synechococcus.

In this study, the tolerance to salt stress of the photosynthetic machinery was examined in relation to the effects of the genetic enhancement of the unsaturation of fatty acids in membrane lipids in wild-type and desA+ cells of Synechococcus sp. PCC 7942. Wild-type cells synthesized saturated and mono-unsaturated fatty acids, whereas desA+ cells, which had been transformed with the desA gene for the Delta12 acyl-lipid desaturase of Synechocystis sp. PCC 6803, also synthesized di-unsaturated fatty acids. Incubation of wild-type and desA+ cells with 0.5 M NaCl resulted in the rapid loss of the activities of photosystem I, photosystem II, and the Na+/H+ antiport system both in light and in darkness. However, desA+ cells were more tolerant to salt stress and osmotic stress than the wild-type cells. The extent of the recovery of the various photosynthetic activities from the effects of 0.5 M NaCl was much greater in desA+ cells than in wild-type cells. The photosystem II activity of thylakoid membranes from desA+ cells was more resistant to 0.5 M NaCl than that of membranes from wild-type cells. These results demonstrated that the genetically engineered increase in unsaturation of fatty acids in membrane lipids significantly enhanced the tolerance of the photosynthetic machinery to salt stress. The enhanced tolerance was due both to the increased resistance of the photosynthetic machinery to the salt-induced damage and to the increased ability of desA+ cells to repair the photosynthetic and Na+/H+ antiport systems.

Redox characteristics of manganese and cobalt complexes obtained from pyridine N-oxide.

Manganese and cobalt complexes, using pyridine N-oxide as ligand, have been synthesized, and their cyclic and square-wave voltammetric measurements have been carried out. The results reveal that the complexes exhibit different voltammetric pattern, which suggests that the redox processes are most probably metal-centered. In both complexes, extra redox activity is observed once the potential exceeds certain value of the voltage. The observation of an oxidation wave in manganese complex at + 0.75 V vs. Ag/AgCl or + 0.95 V vs. NHE strongly suggests that this complex can bring about oxidation of water and can, thus, serve as a synthetic analogue of water oxidizing complex (WOC) of PS II.

Ionic and osmotic effects of NaCl-induced inactivation of photosystems I and II in Synechococcus sp.

We report here that osmotic effects and ionic effects are both involved in the NaCl-induced inactivation of the photosynthetic machinery in the cyanobacterium Synechococcus sp. PCC 7942. Incubation of the cyanobacterial cells in 0.5 M NaCl induced a rapid and reversible decline and subsequent slow and irreversible loss of the oxygen-evolving activity of photosystem (PS) II and the electron transport activity of PSI. An Na(+)-channel blocker protected both PSII and PSI against the slow, but not the rapid, inactivation. The rapid decline resembled the effect of 1.0 M sorbitol. The presence of both an Na(+)-channel blocker and a water-channel blocker protected PSI and PSII against the short- and long-term effects of NaCl. Salt stress also decreased cytoplasmic volume and this effect was enhanced by the Na(+)-channel blocker. Our observations suggested that NaCl had both osmotic and ionic effects. The osmotic effect decreased the amount of water in the cytosol, rapidly increasing the intracellular concentration of salts. The ionic effect was caused by an influx of Na(+) ions through potassium/Na(+) channels that also increased concentrations of salts in the cytosol and irreversibly inactivated PSI and PSII.

Inactivation of photosystems I and II in response to osmotic stress in Synechococcus. Contribution of water channels.

The effects of osmotic stress due to sorbitol on the photosynthetic machinery were investigated in the cyanobacterium Synechococcus R-2. Incubation of cells in 1.0 M sorbitol inactivated photosystems I and II and decreased the intracellular solute space by 50%. These effects of sorbitol were reversible: Photosynthetic activity and cytoplasmic volume returned to the original values after removal of the osmotic stress. A blocker of water channels prevented the osmotic-stress-induced inactivation and shrinkage of the intracellular space. It also prevented the recovery of photosynthetic activity and cytoplasmic volume when applied just before release from osmotic stress. Inhibition of protein synthesis by lincomycin had no significant effects on the inactivation and recovery processes, an observation that suggests that protein synthesis was not involved in these processes. Our results suggest that osmotic stress decreased the amount of water in the cytoplasm via the efflux of water through water channels (aquaporins), with resultant increases in intracellular concentrations of ions and a decrease in photosynthetic activity.