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Adenine nucleotides are essential in countless processes within the cellular metabolism. In plants, ATP is mainly produced in chloroplasts and mitochondria through photophosphorylation and oxidative phosphorylation, respectively. Thus, efficient adenylate transport systems are required for intracellular energy partitioning between the cell organelles. Adenylate carriers present in different subcellular compartments have been previously identified and biochemically characterized in plants. Here, by using data-mining bioinformatics tools, we propose how, and to what extent, these carriers integrate energy metabolism within a plant cell under different environmental conditions. We demonstrate that the expression pattern of the corresponding genes is variable under different environmental conditions, suggesting that specific adenylate carriers have distinct and nonredundant functions in plants.

Plant thylakoids have a typical stacking structure, which is the site of photosynthesis, including light-harvesting, water-splitting, and adenosine triphosphate (ATP) production. This stacking structure plays a key role in exchange of substances with extremely high efficiency and minimum energy consumption through photosynthesis. Herein we report an artificially designed honeycomb multilayer for photophosphorylation. To mimic the natural thylakoid stacking structure, the multilayered photosystem II (PSII)-ATP synthase-liposome system is fabricated via layer-by-layer (LbL) assembly, allowing the three-dimensional distributions of PSII and ATP synthase. Under light illumination, PSII splits water into protons and generates a proton gradient for ATP synthase to produce ATP. Moreover, it is found that the ATP production is extremely associated with the numbers of PSII layers. With such a multilayer structure assembled via LbL, one can better understand the mechanism of PSII and ATP synthase integrated in one system, mimicking the photosynthetic grana structure. On the other hand, such an assembled system can be considered to improve the photophosphorylation.

We attempted to elucidate possible reasons of a decline in fresh and dry mass accumulation by Chinese cabbage (Brassica chinensis L.) plants under combined narrowband red and blue light emitting diodes (LEDs) in comparison with illumination by a broad-spectrum high-pressure sodium lamps (HPSL) of equal photosynthetically active radiation intensity. Analysis of photosynthetic activity, sugar content and composition, antioxidant activity, and membrane peroxidation revealed neither inhibition of nor damage to the photosynthetic apparatus. There was also no detectable oxidative stress and related photoassimilate loss, the source-sink relations were also unimpaired in LED-grown plants. Our findings suggest that the light distribution in the plant canopy might be an essential factor limiting plant growth under the LED light. The results are discussed in view of the role of the radiation in the yellow–green range of the spectrum in driving photosynthesis.

The present study was conducted to examine the effects of increasing concentrations of chromium (Cr(6+)) (0, 25, 50, 100, and 200 μmol) on rice (Oryza sativa L.) morphological traits, photosynthesis performance, and the activities of antioxidative enzymes. In addition, the ultrastructure of chloroplasts in the leaves of hydroponically cultivated rice (O. sativa L.) seedlings was analyzed. Plant fresh and dry weights, height, root length, and photosynthetic pigments were decreased by Cr-induced toxicity (200 μM), and the growth of rice seedlings was starkly inhibited compared with that of the control. In addition, the decreased maximum quantum yield of primary photochemistry (Fv/Fm) might be ascribed to the decreased the number of active photosystem II reaction centers. These results were confirmed by inhibited photophosphorylation, reduced ATP content and its coupling factor Ca(2+)-ATPase, and decreased Mg(2+)-ATPase activities. Furthermore, overtly increased activities of antioxidative enzymes were observed under Cr(6+) toxicity. Malondialdehyde and the generation rates of superoxide (O2̄) also increased with Cr(6+) concentration, while hydrogen peroxide content first increased at a low Cr(6+) concentration of 25 μM and then decreased. Moreover, transmission electron microscopy showed that Cr(6+) exposure resulted in significant chloroplast damage. Taken together, these findings indicate that high Cr(6+)concentrations stimulate the production of toxic reactive oxygen species and promote lipid peroxidation in plants, causing severe damage to cell membranes, degradation of photosynthetic pigments, and inhibition of photosynthesis.

Chloroplasts utilize photons from solar radiation to synthesize energy-rich molecules of ATPs and NADPHs, which are further used in active cellular processes. Multiprotein complexes (MPCs), including photosystems (PSII and PSI), and the cellular architecture responsible for generation of the proton motive force and the subsequent photophosphorylation, mediate the task of ATP and NADPH synthesis. Both photosystems and other multiprotein assemblies are embedded in thylakoid membranes. Advances in techniques used to study structural biology, biophysics, and comparative genomics and proteomics have enabled us to gain insights of structure, function, and localization of each individual component of the photosynthetic apparatus. An efficient coordination among MPCs is essential for normal functioning of photosynthesis, but there are various stressors that might directly or indirectly interact with photosynthetic components and processes. Cadmium is one of the toxic heavy metals that interact with photosynthetic components and damage photosystems and other MPCs in thylakoids. In plants, iron deficiency shows similar symptoms as those caused by Cd. Our article provides a general overview of chloroplast structure and a critical account of Cd-induced changes in photosystems and other MPCs in thylakoids, and suggests the possible mechanisms involved in mediating these changes. The connection between Cd-induced Fe deficiency and the elevated Cd toxicity under the Fe-deficient condition was also discussed.

Like the evolutionary related F1FO ATP synthases and V1VO ATPases, the A1AO ATP synthases from archaea are multisubunit, membrane-bound transport machines that couple ion flow to the synthesis of ATP. Although the subunit composition is known for at least two species, nothing is known so far with respect to the function of individual subunits or amino acid residues. To pave the road for a functional analysis of A1AO ATP synthases, we have cloned the entire operon from Methanosarcina mazei into an expression vector and produced the enzyme in Escherichia coli. Inverted membrane vesicles of the recombinants catalyzed ATP synthesis driven by NADH oxidation as well as artificial driving forces. Δ μ ˜ H + as well as ΔpH were used as driving forces which is consistent with the inhibition of NADH-driven ATP synthesis by protonophores. Exchange of the conserved glutamate in subunit c led to a complete loss of ATP synthesis, proving that this residue is essential for H+ translocation. Exchange of two conserved arginine residues in subunit a has different effects on ATP synthesis. The role of these residues in ion translocation is discussed.

Rhodospirillum rubrum has the potential for biomass resource recycling combined with sewage purification. However, low biomass production and yield restricts the potential for sewage purification. This research investigated the improvement of biomass production, yield and organics reduction by Mg 2+ in R. rubrum wastewater treatment. Results showed that with optimal dosage (120 mg/L), biomass production reached 4,000 mg/L, which was 1.5 times of that of the control group. Biomass yield was improved by 43.3%. Chemical oxygen demand (COD) removal reached over 90%. Hydraulic retention time was shortened by 25%. Mechanism analysis indicated that Mg 2+ enhanced the isocitrate dehydrogenase and Ca 2+ /Mg 2+ -ATPase activities, bacteriochlorophyll content on respiration and photophosphorylation. These effects then enhanced ATP production, which led to more biomass accumulation and COD removal. With 120 mg/L Mg 2+ dosage, the isocitrate dehydrogenase and Ca 2+ /Mg 2+ -ATPase activities, bacteriochlorophyll content, ATP production were improved, respectively, by 33.3%, 50%, 67%, 41.3% compared to those of the control group.

The effect of an increase in the viscosity of the medium on cyclic photophosphorylation in chloroplast thylakoids and the Ca2+-dependent ATP hydrolysis by the chloroplast coupling factor CF1 was studied. Using 0.1–0.2 mM ADP, it was found that the rate of ATP synthesis decreases after the addition of various agents that increase the viscosity of the medium (sucrose, dextran 40, or polyethylene glycol 6000) provided that these agents cause neither uncoupling nor electron-transport inhibition in the absence of ADP. Dextran and polyethylene glycol inhibited ATP synthesis by 50% when their concentrations were much lower (6–10%) than that of sucrose (30–40%), while 50% inhibition of the Ca2+-dependent ATP hydrolysis by CF1-ATPase was observed at higher concentrations of dextran and polyethylene glycol (9–13%) and lower concentrations of sucrose (about 20%). For ADP, the effective Michaelis constant (KM) was shown to increase by factors of 2–3 with increasing viscosity, while the maximum rate of cyclic photophosphorylation remained virtually unchanged. The dependence of KM on the medium viscosity can serve as a criterion for the operation of diffusion-controlled photophosphorylation. Possible mechanisms of the diffusion of ADP and ATP are discussed.

Since solar light energy is the source of all renewable biological energy, the direct usage of light energy by bacterial cell factory has been a very attractive concept, especially using light energy to promote anaerobic fermentation growth and even recycle low-energy carbon source when energy is the limiting factor. Proteorhodopsin(PR), a light-driven proton pump proven to couple with ATP synthesis when expressed heterogeneously, is an interesting and simple option to enable light usage in engineered strains. However, although it was reported to influence fermentation in some cases, heterogeneous proteorhodopsin expression was never shown to support growth advantage or cause metabolic shift by photophosphorylation so far. Hereby, we presented the first experimental evidence that heterogeneously expressed proteorhodopsin can provide growth advantage and cause ATP-dependent metabolism shift of acetate and lactate changes in Escherichia coli at anaerobic condition. Those discoveries suggest further application potential of PR in anaerobic fermentation where energy is a limiting factor.

The fundamentals of oxidative phosphorylation and photophosphorylation are revisited. New experimental data on the involvement of succinate and malate anions respectively in oxidative phosphorylation and photophosphorylation are presented. These new data offer a novel molecular mechanistic explanation for the energy coupling and ATP synthesis carried out in mitochondria and chloroplast thylakoids. The mechanism does not suffer from the flaws in Mitchell's chemiosmotic theory that have been pointed out in many studies since its first appearance 50 years ago, when it was hailed as a ground-breaking mechanistic explanation of what is perhaps the most important process in cellular energetics. The new findings fit very well with the predictions of Nath's torsional mechanism of energy transduction and ATP synthesis. It is argued that this mechanism, based on at least 15 years of experimental and theoretical work by Sunil Nath, constitutes a fundamentally different theory of the energy conversion process that eliminates all the inconsistencies in Mitchell's chemiosmotic theory pointed out by other authors. It is concluded that the energy-transducing complexes in oxidative phosphorylation and photosynthesis are proton-dicarboxylic acid anion cotransporters and not simply electrogenic proton translocators. These results necessitate revision of previous theories of biological energy transduction, coupling, and ATP synthesis. The novel molecular mechanism is extended to cover ATP synthesis in prokaryotes, in particular to alkaliphilic and haloalkaliphilic bacteria, essentially making it a complete theory addressing mechanistic, kinetic, and thermodynamic details. Finally, based on the new interpretation of oxidative phosphorylation, quantitative values for the P/O ratio, the amount of ATP generated per redox package of the reduced substrates, are calculated and compared with experimental values for fermentation on different substrates. It is our hope that the presentation of oxidative phosphorylation and photophosphorylation from a wholly new perspective will rekindle scientific discussion of a key process in bioenergetics and catalyze new avenues of research in a truly interdisciplinary field. Biotechnol. Bioeng. 2015;112: 429–437. © 2014 Wiley Periodicals, Inc.

The ozone depletion has caused plants to be exposed to an increased penetration of solar ultraviolet-B (UV-B) radiation. Enhanced UV-B radiation may have influence on biological functions of plant in many aspects including inhibition of photosynthesis. It is evident that UV-B can potentially impair the performance of all three main component processes of photosynthesis, the photophosphorylation reactions of the thylakoid membrane, the CO2-fixation reactions of the Calvin cycle and stomatal control of CO2 supply. Owing to these depressed reactions, the production and allocation of carbohydrates might be markedly affected, and therefore, the growth and development of plant are distinctly reduced. In this review paper, we provide basic theory and further researches in terms of photosynthesis and carbohydrate synthesis in response to elevated UV-B radiation.

Some anaerobic archaea and bacteria live on substrates that do not allow the synthesis of one mol of ATP per mol of substrate via substrate level phosphorylation (SLP). Energy conservation in these cases is only possible by a chemiosmotic mechanism that involves the generation of an electrochemical ion gradient across the cytoplasmic membrane that then drives ATP synthesis via an ATP synthase. The minimal amount of energy required for ATP synthesis is thus dependent on the magnitude of the electrochemical ion gradient, the phosphorylation potential in the cell and the ion/ATP ratio of the ATP synthase. It was always thought that the minimum biological energy quantum is defined as the amount of energy required to translocate one ion across the cytoplasmic membrane. We will discuss the thermodynamics of the reactions involved in chemiosmosis and describe the limitations for ion transport and ATP synthesis that led to the proposal that at least −20 kJ/mol are required for ATP synthesis. We will challenge this hypothesis by arguing that the enzyme energizing the membrane may translocate net less than one ion: By using a primary pump connected to an antiporter module a stoichiometry below one can be obtained, implying that the minimum biological energy quantum that sustains life is even lower than assumed to date.

The mutant F54 of the unicellular green alga Chlamydomonas reinhardii is not able to perform photophos-phorylation. Nevertheless, it grows on acetate and the chloroplasts accomplish most of their energy-requiring synthetic processes. However, no light-dependent chloroplast protein synthesis could be detected in intact F54 chloroplasts isolated from a cell wall-deficient double mutant F54-cw-15. Exogenous ATP was not able to induce this in organello protein synthesis to an appreciable degree. In contrast, the strictly ATP-dependent protein synthesis was stimulated very efficiently by glyceraldehyde-3-phosphate, dihydroxy-acetone phosphate and glycerol-3-phosphate, but strongly inhibited by 3-phosphoglycerate. These compounds can be transported across the envelope membrane by the triose phosphate translocator. Pyridoxal phosphate, a specific inhibitor of the translocator, abolished the stimulation by triose phosphates. Spermidine, which activates initiation of translation in chloroplasts, enhanced triose phosphate-stimulated protein synthesis even further. In the dark, no stimulation was observed, indicating that a light-dependent reaction was also involved in this kind of ATP production in chloroplasts. The results suggest that chloroplasts defective in photophosphorylation recruit their energy via an ATP shuttle which was shown in this study to import rather than export ATP across the chloroplast envelope

The chloroplast ATP synthase catalyzes the light-driven synthesis of ATP and is activated in the light and inactivated in the dark by redox-modulation through the thioredoxin system. It has been proposed that this down-regulation is important for preventing wasteful hydrolysis of ATP in the dark. To test this proposal, we compared the effects of extended dark exposure in Arabidopsis lines expressing the wild-type and mutant forms of ATP synthase that are redox regulated or constitutively active. In contrast to the predictions of the model, we observed that plants with wild-type redox regulation lost photosynthetic capacity rapidly in darkness, whereas those expressing redox-insensitive form were far more stable. To explain these results, we propose that in wild-type plants, down-regulation of ATP synthase inhibits ATP hydrolysis, leading to dissipation of thylakoid proton motive force (pmf) and subsequent inhibition of protein transport across the thylakoid through the twin arginine transporter (Tat)-dependent and Sec-dependent import pathways, resulting in the selective loss of specific protein complexes. By contrast, in mutants with a redox-insensitive ATP synthase, pmf is maintained by ATP hydrolysis, thus allowing protein transport to maintain photosynthetic activities for extended periods in the dark. Hence, a basal level of Tat-dependent, as well as, Sec-dependent import activity, in the dark helps replenishes certain components of the photosynthetic complexes and thereby aids in maintaining overall complex activity. However, the influence of a dark pmf on thylakoid protein import, by itself, could not explain all the effects we observed in this study. For example, we also observed in wild type plants a large transient buildup of thylakoid pmf and nonphotochemical exciton quenching upon sudden illumination of dark adapted plants. Therefore, we conclude that down-regulation of the ATP synthase is probably not related to preventing loss of ATP per se. Instead, ATP synthase redox regulation may be impacting a number of cellular processes such as (1) the accumulation of chloroplast proteins and/or ions or (2) the responses of photosynthesis to rapid changes in light intensity. A model highlighting the complex interplay between ATP synthase regulation and pmf in maintaining various chloroplast functions in the dark is presented. Significance Statement: We uncover an unexpected role for thioredoxin modulation of the chloroplast ATP synthase in regulating the dark-stability of the photosynthetic apparatus, most likely by controlling thylakoid membrane transport of proteins and ions.

The vital coupled processes of oxidative phosphorylation and photosynthetic phosphorylation synthesize molecules of adenosine-5'-triphosphate (ATP), the universal biological energy currency, and sustain all life on our planet. The chemiosmotic theory of energy coupling in oxidative and photophosphorylation was proposed by Mitchell >50years ago. It has had a contentious history, with part of the accumulated body of experimental evidence supporting it, and part of it in conflict with the theory. Although the theory was strongly criticized by many prominent scientists, the controversy has never been resolved. Here, the mathematical steps of Mitchell's original derivation leading to the principal equation of the chemiosmotic theory are scrutinized, and a fundamental flaw in them has been identified. Surprisingly, this flaw had not been detected earlier. Discovery of such a defect negates, or at least considerably weakens, the theoretical foundations on which the chemiosmotic theory is based. Ad hoc or simplistic ways to remedy this defect are shown to be scientifically unproductive and sterile. A novel two-ion theory of biological energy coupling salvages the situation by rectifying the fundamental flaw in the chemiosmotic theory, and the governing equations of the new theory have been shown to accurately quantify and predict extensive recent experimental data on ATP synthesis by F1FO-ATP synthase without using adjustable parameters. Some major biological implications arising from the new thinking are discussed. The principles of energy transduction and coupling proposed in the new paradigm are shown to be of a very general and universal nature. It is concluded that the timely availability after a 25-year research struggle of Nath's torsional mechanism of energy transduction and ATP synthesis is a rational alternative that has the power to solve the problems arising from the past, and also meet present and future challenges in this important interdisciplinary field of research.

To investigate the effects of Nitrogen (N):phosphorus (P) ratio and solar ultraviolet radiation (UVR) on the growth and photophosphorylation of oceanic phytoplankton, the effects of UVR and N:P ratio on K. mikimotoi were evaluated. K. mikimotoi cells were cultured in artificial seawater (ASW) under five different N:P ratios (1:1, 16:1, 50:1, 100:1 and 200:1) for 15 days (phase 1: 1–5 day; phase 2: 6–10 day; phase 3: 11–15 days). Next, K. mikimotoi cultures were exposed to photosynthetically active radiation (PAR), PAB (PAR + UV-A + UV-B) and PA (PAR + UV-A), respectively. Finally, K. mikimotoi cells grown under the Redfield ratio (16:1) had the largest growth rate (0.257day−1), highest pigment concentrations (chlorophyll a (Chla): 0.465 × 10− 5 μg cell−1, carotenoid (Caro): 0.249 × 10−5 μg cell−1) and maximum superoxide dismutase (SOD) activity (0.9 U × 10−6 cell−1) compared with those grown under other N:P ratios. The UV-absorbing compounds’ (UVabc) absorbance was largest at the N:P ratio of 50:1 during the range of 310–360 nm, with a relatively higher value at the N:P ratio of 16:1. UV intensity was positively correlated with photoinhibition. K. mikimotoi cells grown at the N:P ratio of 16:1 showed the smallest photoinhibition compared to those grown at other N:P ratios under the PAR treatment with the largest r:k ratio; similar results were found for both the PA and PAB treatments. The Redfield ratio of 16:1 is optimal for the growth and photophosphorylation of K. mikimotoi. The weakest UVR-induced photoinhibition at this ratio may be attributed to the highest photosystem II (PSII) repair rate and SOD activity.

Nitric oxide (NO) is emerging as a signaling molecule in plants. Its metabolism, site and mode of action in chloroplasts are still not clear. Chloroplasts are emerging as an alternative site for NO synthesis in plants. However, exogenous NO donors show direct evidence on the action of this molecule on chloroplasts under stress as well non-stress conditions. Nitric oxide is also implicated in the development and senescence of the organelle. The effects of NO on chloroplasts, particularly on photosynthetic and antioxidative processes are described. The target sites and probable sites of action are enumerated.

Rubrivivax gelatinosus has the potential of biomass resource recycling combined with sewage purification. However, low biomass production and yield restricts the potential for sewage purification. Thus, this research investigated the improvement of biomass production and yield and organics reduction by Fe3+ in R. gelatinosus wastewater treatment. Results showed that 10–30 mg/L Fe3+ improved biomass yield in wastewater to a level found in culture medium. With optimal dosage (20 mg/L), biomass production reached 4,300 mg/L, which was 1.67 times that of the control group. Biomass yield was improved by 43.3%. Chemical oxygen demand (COD) removal reached above 91%. Hydraulic retention time was shortened by 25%. Mechanism analysis indicated that Fe3+ enhanced the succinate and NADH dehydrogenase activities and, bacteriochlorophyll content in three energy metabolism pathways. These effects then enhanced adenosine triphosphate (ATP) production, which led to more biomass accumulation and COD removal. With 20 mg/L Fe2+ dosage, succinate and NADH dehydrogenase, coproporphyrinogen III oxidase activities, bacteriochlorophyll content and ATP production were improved, respectively, by 48.4, 50.8, 50, 67 and 56% compared to those of the control group.

Physiological, biochemical and electron microscopy analyses were used to investigate the photosynthetic performance of flag leaves in rice white stripe mutant 6001 during the senescence process. Results showed that the chlorophyll content at the heading and milk-ripe stages in rice mutant 6001 were about 34.78% and 3.00% less than those in wild type 6028, respectively. However, the chlorophyll content at the fully-ripe stage in rice mutant 6001 was higher than that in wild type 6028. At the heading stage, the net photosynthetic rate (Pn) in rice mutant 6001 was lower than that in wild type 6028. Rice mutant 6001 also exhibited a significantly slower decrease rate of Pn than wild type 6028 during the senescence progress, especially at the later stage. Furthermore, Ca2+-ATPase, Mg2+-ATPase and photophosphorylation activities exhibited the similar trends as the Pn. During the senescence process, the 68 kDa polypeptide concentrations in the thylakoid membrane proteins exhibited a significant change, which was one of the critical factors that contributed to the observed change in photosynthesis. We also observed that the chloroplasts of rice mutant 6001 exhibited higher integrity than those of wild type 6028, and the chloroplast membrane of rice mutant 6001 disintegrated more slow during the senescence process. In general, rice mutant 6001 had a relatively slower senescence rate than wild type 6028, and exhibited anti-senescence properties.

Photosynthetic pigments, biochemical activities and chlorophyll a fluorescence kinetics were investigated to survey the photosynthetic characteristics of Ginkgo biloba L. during leaf growth. The content of total chlorophyll increased rapidly while the content of carotenoids changed a little. The content of ATP, the activity of O 2 evolution of chloroplasts, the electron transport activities, the activity of photophosphorylation and the activities of Ca 2+ - and Mg 2+ - ATPase were strengthened. All leaves at various growing stages exhibited typical chlorophyll ? fluorescence transient, the intensity of fluorescence in the chlorophyll ? fluorescence transient (OJIP) increased during leaf growth. Photosynthetic abilities gradually increased as the leaves grew. DOI: http://dx.doi.org/10.3329/bjb.v43i1.19749 Bangladesh J. Bot. 43 (1): 73-77, 2014 (June)

Currently light emitting diodes (LEDs) are considered to be most preferable source for space plant growth facilities. We performed a complex study of growth and photosynthesis in Chinese cabbage plants (Brassica chinensis L.) grown with continuous LED lighting based on red (650 nm) and blue (470 nm) LEDs with a red to blue photon ratio of 7:1. Plants grown with high-pressure sodium (HPS) lamps were used as a control. PPF levels used were about 100 μmol/(m2 s) (PPF 100) and nearly 400 μmol/(m2 s) (PPF 400). One group of plants was grown with PPF 100 and transferred to PPF 400 at the age of 12 days. Plants were studied at the age of 15 and 28 days (harvest age); some plants were left to naturally end their life cycle. We studied a number of parameters reflecting different stages of photosynthesis: photosynthetic pigment content; chlorophyll fluorescence parameters (photosystem II quantum yield, photochemical and non-photochemical chlorophyll fluorescence quenching); electron transport rate, proton gradient on thylakoid membranes (ΔpH), and photophosphorylation rate in isolated chloroplasts. We also tested parameters reflecting plant growth and productivity: shoot and root fresh and dry weight, sugar content and ascorbic acid content in shoots. Our results had shown that at PPF 100, plants grown with LEDs did not differ from control plants in shoot fresh weight, but showed substantial differences in photophosphorylation rate and sugar content. Differences observed in plants grown with PPF 100 become more pronounced in plants grown with PPF 400. Most parameters characterizing the plant photosynthetic performance, such as photosynthetic pigment content, electron transport rate, and ΔpH did not react strongly to light spectrum. Photophosphorylation rate differed strongly in plants grown with different spectrum and PPF level, but did not always reflect final plant yield. Results of the present work suggest that narrow-band LED lighting caused changes in Chinese cabbage plants on levels of the photosynthetic apparatus and the whole plant, concerning its development and adaptation to a varying PPF level.

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.

Some anaerobic archaea live on substrates that do not allow the synthesis of 1 mol of ATP per mol of substrate. Energy conservation in these cases is only possible by a chemiosmotic mechanism that involves the generation of an electrochemical ion gradient across the cytoplasmatic membrane that then drives ATP synthesis via an A1AO ATP synthase. The minimal amount of energy required is thus depending on the magnitude of the electrochemical ion gradient, the phosphorylation potential, and the ion/ATP ratio of the ATP synthase. Methanogens, Thermococcus, Pyrococcus, and Ignicoccus have evolved different ways to energize their membranes, such as methyltransferases, H+, or NAD+ reducing electron transport systems fueled by reduced ferredoxin or H2 -dependent sulfur reduction that all operate at the thermodynamic limit of life. The structure and function of the enzymes involved are discussed. Despite the differences in membrane energization, they have in common an A1AO ATP synthase that shows an extraordinary divergence in rotor composition and structural adaptations to life under these conditions. In sum, adaptation of anaerobic archaea to energy-limited substrates involves chemiosmotic energy coupling, often with Na+ as coupling ion and a structurally and functionally highly adapted ATP synthase.

ATP synthase is a biological motor that produces a molecule called adenosine tri-phosphate (ATP for short), which acts as the major store of chemical energy in cells. A single molecule of ATP contains three phosphate groups: the cell can remove one of these phosphates to make a molecule called adenosine di-phosphate (ADP) and release energy to drive a variety of biological processes. ATP synthase sits in the membranes that separate cell compartments or form barriers around cells. When cells break down food they transport hydrogen ions across these membranes so that each side of the membrane has a different level (or “concentration”) of hydrogen ions. Movement of hydrogen ions from an area with a high concentration to a low concentration causes ATP synthase to rotate like a turbine. This rotation of the enzyme results in ATP synthase adding a phosphate group to ADP to make a new molecule of ATP. In certain conditions cells need to switch off the ATP synthase and this is done by changing the shape of the central shaft in a process called autoinhibition, which blocks the rotation. The ATP synthase from a bacterium known as E. coli – which is commonly found in the human gut –has been used as a model to study how this biological motor works. However, since the precise details of the three-dimensional structure of ATP synthase have remained unclear it has been difficult to interpret the results of these studies. Sobti et al. used a technique called Cryo-electron microscopy to investigate the structure of ATP synthase from E. coli. This made it possible to develop a three-dimensional model of the ATP synthase in its autoinhibited form. The structural data could also be split into three distinct shapes that relate to dwell points in the rotation of the motor where the rotation has been inhibited. These models further our understanding of ATP synthases and provide a template to understand the findings of previous studies. Further work will be needed to understand this essential biological process at the atomic level in both its inhibited and uninhibited form. This will reveal the inner workings of a marvel of the natural world and may also lead to the discovery of new antibiotics against related bacteria that cause diseases in humans.

ATP synthases (FoF1-ATPases) of chloroplasts, mitochondria, and bacteria catalyze ATP synthesis or hydrolysis coupled with the transmembrane transfer of protons or sodium ions. Their activity is regulated through their reversible inactivation resulting from a decreased transmembrane potential difference. The inactivation is believed to conserve ATP previously synthesized under conditions of sufficient energy supply against unproductive hydrolysis. This review is focused on the mechanism of nucleotide-dependent regulation of the ATP synthase activity where the so-called noncatalytic nucleotide binding sites are involved. Properties of these sites varying upon free enzyme transition to its membrane-bound form, their dependence on membrane energization, and putative mechanisms of noncatalytic site-mediated regulation of the ATP synthase activity are discussed.

A model of photophosphorylation of ADP to ATP under UV and blue light with the use of substances available in the prebiotic period of evolution is proposed. It is shown that the photoactive pigments of flavin and pterin nature formed along with polyamino acids during thermal synthesis of “proteinoids” from a mixture of amino acids initiate the process of photophosphorylation of ADP to ATP. Photophosphorylation occurs on proteinoid-silicate matrices of two types: (1) in the microspheres formed of proteinoids in the presence of polysilicic acid and (2) on the matrices obtained by adsorption of proteinoids on silicate particles.

Manganese (Mn) is an essential element for plants which intervenes mainly in photosynthesis. In this study we establish that manganese nanoparticles (MnNP) work as a better micronutrient than commercially available manganese salt, MnSO4 (MS) at recommended doses on leguminous plant mung bean (Vigna radiata) under laboratory condition. At higher doses it does not impart toxicity to the plant unlike MS. MnNP-treated chloroplasts show greater photophosphorylation, oxygen evolution with respect to control and MS-treated chloroplasts as determined by biophysical and biochemical techniques. Water splitting by an oxygen evolving complex is enhanced by MnNP in isolated chloroplast as confirmed by polarographic and spectroscopic techniques. Enhanced activity of the CP43 protein of a photosystem II (PS II) Mn4Ca complex influenced better phosphorylation in the electron transport chain in the case of MnNP-treated chloroplast, which is evaluated by sodium dodecyl sulfate polyacrylamide gel electrophoresis and corresponding Western blot analysis. To the best of our knowledge this is the first report to augment photosynthesis using MnNP and its detailed correlation with different molecular, biochemical and biophysical parameters of photosynthetic pathways. At effective dosage, MnNP is found to be biosafe both in plant and animal model systems. Therefore MnNP would be a novel potential nanomodulator of photochemistry in the agricultural sector.

The numerous data suggest an important role of phytohormones, particularly cytokinins, in regulation of plants growth and development. The cytokinins stimulates the cells division, takes part in cells differentiation and other physiological processes. In the present paper the effect of N,N-diphenylurea (DPU), a compound possessing cytokinine activity, on the rate of photophosphorylation and thylakoid membrane structure of chloroplasts in milky phase as well as on amino acid composition of reserve protein of barley ( Hordeum vulgare L.) of the Trumpf and Odesskii varieties and wheat ( Triticum aestivum L.) of the Moskovskaya 35 and Tulunskaya varieties was investigated. The treatment with DPU changed the rates of cyclic and acyclic photophosphorylation of thylakoid membrane isolated from flag leaves of treated plants and induced destructive changes in chloroplasts. The changes in percentage ratio of a number of amino acids in reserve grain protein, especially proline, were shown. The modifications in mesophyll cells of chloroplasts after DPU treatment suggest that an action of this compound at the beginning of milky phase accelerates the process of plants aging, but its action at the beginning of flowering phase results in converse effect. A conclusion was done that DPU controls energy metabolism in the leaves and protein exchange in grain of wheat and barley plants.

A model for abiotic photophosphorylation of adenosine diphosphate by orthophosphate with the formation of adenosine triphosphate was studied. The model was based on the photochemical activity of the abiogenic conjugates of pigments with the polymeric material formed after thermolysis of amino acid mixtures. The pigments formed showed different fluorescence parameters depending on the composition of the mixture of amino acid precursors. Thermolysis of the mixture of glutamic acid, glycine, and lysine (8:3:1) resulted in a predominant formation of a pigment fraction which had the fluorescence maximum at 525 nm and the excitation band maxima at 260, 375, and 450 nm and was identified as flavin. When glycine in the initial mixture was replaced with alanine, a product formed whose fluorescence parameters were typical to pteridines (excitation maximum at 350 nm, emission maximum at 440 nm). When irradiated with the quasi-monochromatic light (over the range 325-525 nm), microspheres in which flavin pigments were prevailing showed a maximum photophosphorylating activity at 375 and 450 nm, and pteridine-containing chromoproteinoid microspheres were most active at 350 nm. The positions and the relative height of maxima in the action spectra correlate with those in the excitation spectra of the pigments, which point to the involvement of abiogenic flavins and pteridines in photophosphorylation.

The molecular mechanism by which the membrane-embedded FO sector of the mitochondrial ATP synthase translocates protons, thus dissipating the transmembrane protonmotive force and leading to ATP synthesis, involves the neutralization of the carboxylate residues of the c-ring. Carboxylates are thought to constitute the binding sites for ion translocation. In order to cast light on this mechanism, we exploited N,N’-dicyclohexylcarbodiimide, which covalently binds to FO c-ring carboxylates, and ionophores which selectively modulate the transmembrane electric (Δφ) and chemical (ΔpH) gradients such as valinomycin, nigericin and dinitrophenol. ATP hydrolysis was evaluated in mitochondrial preparations and/or inside-out submitochondrial particles from mussel and mammalian tissues under different experimental conditions. The experiments pointed out striking similarities between mussel and mammalian mitochondrial ATP synthase. Our results support the hypothesis that the ATP synthase of Mytilus galloprovincialis induces intersubunit torque generation and translocates H+ by coordinating the hydronium ion (H3O+) in the ion binding site of FO. Our results are consistent with the hypothesis that in mussel mitochondria the main component of the electrochemical gradient driving proton flux and ATP synthesis is Δφ. Therefore, mussel FO probably contains a small c-ring, which implies a low bioenergetic cost of making ATP as in mammals. These features which make mussel mitochondria as efficient in ATP production as mammalian ones may be especially advantageous in facultative aerobic species which intermittently exploit mitochondrial respiration to generate ATP.

The vast majority of life on earth is dependent on harvesting electrochemical potentials over membranes for the synthesis of ATP. Generation of membrane potential often relies on electron transport through membrane protein complexes, which vary among the bioenergetic membranes found in living organisms. In order to maximize the efficient harvesting of the electrochemical potential, energy loss must be minimized, and this is achieved partly by restricting certain events to specific microcompartments, on bioenergetic membranes. In this review we will describe the characteristics of the energy-converting supramolecular structures involved in oxidative phosphorylation in mitochondria and bacteria, and photophosphorylation. Efficient function of electron transfer pathways requires regulation of electron flow, and we will also discuss how this is partly achieved through dynamic re-compartmentation of the membrane complexes into different supercomplexes. In addition to supercomplexes, the supramolecular structure of the membrane, and in particular the role of water layers on the surface of the membrane in the prevention of wasteful proton escape (and therefore energy loss), is discussed in detail. In summary, the restriction of energetic processes to specific microcompartments on bioenergetic membranes minimizes energy loss, and dynamic rearrangement of these structures allows for regulation.

STARCH SYNTHASE4 (SS4) is required for proper starch granule initiation in Arabidopsis (Arabidopsis thaliana), although SS3 can partially replace its function. Unlike other starch-deficient mutants, ss4 and ss3/ss4 mutants grow poorly even under long-day conditions. They have less chlorophyll and carotenoids than the wild type and lower maximal rates of photosynthesis. There is evidence of photooxidative damage of the photosynthetic apparatus in the mutants from chlorophyll a fluorescence parameters and their high levels of malondialdehyde. Metabolite profiling revealed that ss3/ss4 accumulates over 170 times more ADP-glucose (Glc) than wild-type plants. Restricting ADP-Glc synthesis, by introducing mutations in the plastidial phosphoglucomutase (pgm1) or the small subunit of ADP-Glc pyrophosphorylase (aps1), largely restored photosynthetic capacity and growth in pgm1/ss3/ss4 and aps1/ss3/ss4 triple mutants. It is proposed that the accumulation of ADP-Glc in the ss3/ss4 mutant sequesters a large part of the plastidial pools of adenine nucleotides, which limits photophosphorylation, leading to photooxidative stress, causing the chlorotic and stunted growth phenotypes of the plants.

17β-estradiol (E2) is considered to modulate the ATP synthase activity through direct binding to the oligomycin sensitive-conferring protein. We have previously demonstrated that E2 increases the amplitude of depolarization associated with the addition of ADP to energized mitochondria (i.e., to initiate a phosphorylative cycle) suggesting a direct action on the phosphorylative system of mitochondria. The purpose of the present study was to investigate the underlying mechanisms responsible for this effect. We show here that E2 modulates the activity of mitochondrial ATP synthase by promoting the intrinsic uncoupling ("slipping") of the ATP synthase. E2 depressed RCR, ADP/O ratio and state 3 respiration, whereas state 4 respiration was increased and VFCCP (uncoupled respiration) remained unaltered. In contrast to the stimulatory effect on state 4 respiration, state 2 respiration and Volig were not affected by E2. The effect of E2 appeared to be directed towards ATP synthase, since glutamate/malate respiration, uncoupled from the electron transport chain, was unaffected by E2. Apparently, E2 allows a proton back-leak through the Fo component of ATP synthase. This action of E2 is dependent on the presence of ATP, is more pronounced at high membrane potentials, and it is reversed by oligomycin (a Fo-ATP synthase inhibitor) but not by resveratrol (a F1-ATP synthase inhibitor). Altogether, our data provide a mechanistic explanation for the effect of E2 at the level of mitochondrial ATP synthase.

Excited flavin molecules can photocatalyze reactions, leading to the accumulation of free energy in the products, and the data accumulated through biochemical experiments and by modeling prebiological processes suggest that flavins were available in the earliest stages of evolution. Furthermore, model experiments have shown that abiogenic flavin conjugated with a polyamino acid matrix, a pigment that photocatalyzes the phosphorylation of ADP to form ATP, could have been present in the prebiotic environment. Indeed, excited flavin molecules play key roles in many photoenzymes and regulatory photoreceptors, and the substantial structural differences between photoreceptor families indicate that evolution has repeatedly used flavins as chromophores for photoreceptor proteins. Some of these photoreceptors are equipped with a light-harvesting antenna, which transfers excitation energy to chemically reactive flavins in the reaction center. The sum of the available data suggests that evolution could have led to the formation of a flavin-based biological converter to convert light energy into energy in the form of ATP.

Cyanophage infecting the marine cyanobacteria Prochlorococcus and Synechococcus require light and host photosystem activity for optimal reproduction. Many cyanophages encode multiple photosynthetic electron transport (PET) proteins, which are presumed to maintain electron flow and produce ATP and NADPH for nucleotide biosynthesis and phage genome replication. However, evidence suggests phage augment NADPH production via the pentose phosphate pathway (PPP), thus calling into question the need for NADPH production by PET. Genes implicated in cyclic PET have since been identified in cyanophage genomes. It remains an open question which mode of PET, cyclic or linear, predominates in infected cyanobacteria, and thus whether the balance is towards producing ATP or NADPH. We sequenced transcriptomes of a cyanophage (P-HM2) and its host (Prochlorococcus MED4) throughout infection in the light or in the dark, and analyzed these data in the context of phage replication and metabolite measurements. Infection was robust in the light, but phage were not produced in the dark. Host gene transcripts encoding high-light inducible proteins and two terminal oxidases (plastoquinol terminal oxidase and cytochrome c oxidase)—implicated in protecting the photosynthetic membrane from light stress—were the most enriched in light but not dark infection. Among the most diminished transcripts in both light and dark infection was ferredoxin–NADP[superscript +] reductase (FNR), which uses the electron acceptor NADP[superscript +] to generate NADPH in linear photosynthesis. The phage gene for CP12, which putatively inhibits the Calvin cycle enzyme that receives NADPH from FNR, was highly expressed in light infection. Therefore, both PET production of NADPH and its consumption by carbon fixation are putatively repressed during phage infection in light. Transcriptomic evidence is thus consistent with cyclic photophosphorylation using oxygen as the terminal electron acceptor as the dominant mode of PET under infection, with ATP from PET and NADPH from the PPP producing the energy and reducing equivalents for phage nucleotide biosynthesis and replication., Gordon and Betty Moore Foundation (GBMF495), National Science Foundation (U.S.) (OCE-1153588 and DBI-0424599), National Institutes of Health (U.S.) (Pre-Doctoral Training Grant T32GM007287)

This work is devoted to critical analysis and reexamination of the problem of lateral heterogeneity of the trans-thylakoid pH difference (ΔpH = pHout − pHin) in thylakoid membranes of chloroplasts. Correct measurements of ΔpH may be complicated by nonuniform partitioning of the protons pumped into the lumen of granal (stacked) and stroma-exposed thylakoids. We have compared results of ΔpH estimations in isolated bean chloroplasts by two different methods. One of the methods is based on the use of pH-sensitive spin-probes. Another approach relies on the analysis of pH-dependent post-illumination reduction of P700+ - oxidized reaction center of photosystem I (PSI). Both methods lead to virtually the same values of ΔpH, as measured in the state of photosynthetic control when the ATP synthase complexes are inactive (ΔpH ~ 2.3–2.5 at pHout ~ 8). Under the photophosphorylation conditions (metabolic state 3), ΔpH decreases due to the proton drain from the lumen to stroma via active ATP synthases (ΔpH ~ 1–2 at pHout ~ 8). In this state, ΔpH values derived from kinetic data are smaller than ΔpH measured with the pH-probing amines. Such a discrepancy can be explained by the coexistence of thylakoids with different pHin established in granal and stromal thylakoids. The kinetic method is equivalent to the use of a “local pH-meter”, which is sensitive to less significant decrease in pHin inside the stroma-exposed thylakoids. Otherwise, pH-indicating probes give information on pHin values averaged out at both granal and stromal thylakoids. Experimental results have been analyzed within the framework of our mathematical model developed for simulation of electron and proton transport processes in laterally heterogeneous thylakoids. The model provides a reasonable description of experimental data, supporting the notion that the long-range diffusion of protons within the lumen and obstructed diffusion of mobile electron carriers (PQH2 and Pc) influence the lateral profiles of pH along the thylakoid membranes. The model predicts significant alkalization of the inter-thylakoid gap and the establishment of nonuniform lateral profiles of ΔpH under the photophosphorylation conditions. These results are discussed in the context of the problem of energy coupling in laterally heterogeneous lamellar system of chloroplasts.

Here we consider the cyanobacterial carbon-concentrating mechanism (CCM) and photorespiration in the context of the regulation of light harvesting, using a conceptual framework borrowed from engineering: modularity. Broadly speaking, biological 'modules' are semi-autonomous functional units such as protein domains, operons, metabolic pathways, and (sub)cellular compartments. They are increasingly recognized as units of both evolution and engineering. Modules may be connected by metabolites, such as NADPH, ATP, and 2PG. While the Calvin-Benson-Bassham Cycle and photorespiratory salvage pathways can be considered as metabolic modules, the carboxysome, the core of the cyanobacterial CCM, is both a structural and a metabolic module. In photosynthetic organisms, which use light cues to adapt to the external environment and which tune the photosystems to provide the ATP and reducing power for carbon fixation, light-regulated modules are critical. The primary enzyme of carbon fixation, RuBisCO, uses CO2 as a substrate, which is accumulated via the CCM. However RuBisCO also has a secondary reaction in which it utilizes O2, a by-product of the photochemical modules, which leads to photorespiration. A complete understanding of the interplay among CCM and photorespiration is predicated on uncovering their connections to the light reactions and the regulatory factors and pathways that tune these modules to external cues. We probe this connection by investigating light inputs into the CCM and photorespiratory pathways in the chromatically acclimating cyanobacterium Fremyella diplosiphon.

Energy conversion in biological systems is underpinned by membrane-bound proton transporters that generate and maintain a proton electrochemical gradient across the membrane which used, e.g. for generation of ATP by the ATP synthase. Here, we have co-reconstituted the proton pump cytochrome bo3 (ubiquinol oxidase) together with ATP synthase in liposomes and studied the effect of changing the lipid composition on the ATP synthesis activity driven by proton pumping. We found that for 100 nm liposomes, containing 5 of each proteins, the ATP synthesis rates decreased significantly with increasing fractions of DOPA, DOPE, DOPG or cardiolipin added to liposomes made of DOPC; with e.g. 5% DOPG, we observed an almost 50% decrease in the ATP synthesis rate. However, upon increasing the average distance between the proton pumps and ATP synthases, the ATP synthesis rate dropped and the lipid dependence of this activity vanished. The data indicate that protons are transferred along the membrane, between cytochrome bo3 and the ATP synthase, but only at sufficiently high protein densities. We also argue that the local protein density may be modulated by lipid-dependent changes in interactions between the two proteins complexes, which points to a mechanism by which the cell may regulate the overall activity of the respiratory chain.

The purple nonsulfur bacterium Rhodopseudomonas palustris grows aerobically using oxidative phosphorylation or anaerobically using photophosphorylation. The oxygen-responsive transcription regulator, PpsR2, regulates the transition to a phototrophic lifestyle by repressing transcription of photosynthesis genes during aerobic growth. Whereas most R. palustris strains have an arginine (Arg) at position 439 in the helix-turn-helix DNA-binding domain of this protein, some strains, including the well-studied strain CGA009, have a cysteine (Cys) at this position. Using allelic exchange, we found that the Cys439 in PpsR2 resulted in increased pigmentation and photosynthetic gene expression under both aerobic and anaerobic conditions. The Cys439 substitution also conferred a growth advantage to R. palustris at low light intensities. This indicates that variation in the PpsR2 protein results in R. palustris strains that have two different thresholds for derepressing photosynthesis genes in response to oxygen and light.

Cyclic electron flow (CEF) around photosystem I (PSI) can protect photosynthetic electron carriers under conditions of stromal over-reduction. The goal of the research reported in this paper was to investigate the responses of both PSI and photosystem II (PSII) to a short-term heat stress in two rice lines with different capacities of cyclic electron transfer, i.e., Q4149 with a high capacity (hcef) and C4023 with a low capacity (lcef). The absorbance change at 820 nm (ΔA820) was used here to assess the charge separation in the PSI reaction center (P700). The results obtained show that short-term heat stress abolishes the ferredoxin-quinone oxidoreductase (FQR)-dependent CEF in rice and accelerates the initial rate of P700 (+) re-reduction. The P700 (+) amplitude was slightly increased at a moderate heat-stress (35°C) because of a partial restriction of FQR but it was decreased following high heat-stress (42°C). Assessment of PSI and PSII activities shows that PSI is more susceptible to heat stress than PSII. Under high temperature, FQR-dependent CEF was completely removed and NDH-dependent CEF was up-regulated and strengthened to a higher extent in C4023 than in Q4149. Specifically, under normal growth temperature, hcef (Q4149) was characterized by higher FQR- and chloroplast NAD(P)H dehydrogenase (NDH)-dependent CEF rates than lcef (C4023). Following thermal stress, the activation of NDH-pathway was 130 and 10% for C4023 and Q4149, respectively. Thus, the NDH-dependent CEF may constitute the second layer of plant protection and defense against heat stress after the main route, i.e., FQR-dependent CEF, reaches its capacity. We discuss the possibility that under high heat stress, the NDH pathway serves as a safety valve to dissipate excess energy by cyclic photophosphorylation and overcome the stroma over-reduction following inhibition of CO2 assimilation and any shortage or lack in the FQR pathway. The potential role of the NDH-dependent pathway during the evolution of C4 photosynthesis is briefly discussed.

The Calvin-Benson cycle and the photorespiratory pathway form the photosynthetic-photorespiratory supercycle that is responsible for nearly all biological CO2 fixation on Earth. In essence, supplementation with the photorespiratory pathway is necessary because the CO2-fixing enzyme of the Calvin-Benson cycle, ribulose 1,5-bisphosphate carboxylase (Rubisco), catalyses several side reactions including the oxygenation of ribulose 1,5-bisphosphate, which produces the noxious metabolite phosphoglycolate. The photorespiratory pathway recycles the phosphoglycolate to 3-phosphoglycerate and in this way allows the Calvin-Benson cycle to operate in the presence of molecular oxygen generated by oxygenic photosynthesis. While the carbon flow through the individual and combined subprocesses is well known, information on their regulatory interaction is very limited. Regulatory feedback from the photorespiratory pathway to the Calvin-Benson cycle can be presumed from numerous inhibitor experiments and was demonstrated in recent studies with transgenic plants. This complexity illustrates that we are not yet ready to rationally engineer photosynthesis by altering photorespiration since despite massive understanding of the core photorespiratory pathway our understanding of its interaction with other pathways and processes remains fragmentary.

After termination of longer-illumination (more than 30 s), the wild type of Synechocystis PCC 6803 showed the oscillation kinetics of post-illumination increase in Chl fluorescence: a fast phase followed by one or two slow phases. Unlike the wild type, ndh-B defective mutant M55 did not show any post-illumination increase under the same conditions, indicating that not only the fast phase, but also the slow phases were related to the NDH-mediated cyclic electron flow around photosystem I (PS I) to plastoquinone (PQ).The fast phase was stimulated by dark incubation or in the presence of Calvin cycle inhibitor, iodoacetamid (IA) or cyclic photophosphorylation cofactor, phenazinemethosulphate (PMS), implying the redox changes of PQ by electrons generated at PS I reduced side, probably NAD(P)H or ferredoxin (Fd). In contrast, the slow phases disappeared after dark starvation or in the presence of IA or PMS, and reappeared by longer re-illumination, suggesting that they are related to the redox changes of PQ by the electrons from the photoreductants produced in carbon assimilation process. Both the fast phase and slow phases were stimulated at high temperature and the slow phase (P2) was promoted by response to high concentration of NaCl. The mutant M55 without both phases could not survive under the stressed conditions.