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To examine the effect of mitochondrial function on photosynthesis, wild-type and transgenic Nicotiana tabacum with varying amounts of alternative oxidase (AOX) were treated with different respiratory inhibitors. Initially, each inhibitor increased the reduction state of the chloroplast electron transport chain, most severely in AOX knockdowns and least severely in AOX overexpressors. This indicated that the mitochondrion was a necessary sink for photo-generated reductant, contributing to the 'P700 oxidation capacity' of photosystem I. Initially, the Complex III inhibitor myxothiazol and the mitochondrial ATP synthase inhibitor oligomycin caused an increase in photosystem II regulated non-photochemical quenching not evident with the Complex III inhibitor antimycin A (AA). This indicated that the increased quenching depended upon AA-sensitive cyclic electron transport (CET). Following 12 h with oligomycin, the reduction state of the chloroplast electron transport chain recovered in all plant lines. Recovery was associated with large increases in the protein amount of chloroplast ATP synthase and mitochondrial uncoupling protein. This increased the capacity for photophosphorylation in the absence of oxidative phosphorylation and enabled the mitochondrion to act again as a sink for photo-generated reductant. Comparing the AA and myxothiazol treatments at 12 h showed that CET optimized photosystem I quantum yield, depending upon the P700 oxidation capacity. When this capacity was too high, CET drew electrons away from other sinks, moderating the P700+ amount. When P700 oxidation capacity was too low, CET acted as an electron overflow, moderating the amount of reduced P700. This study reveals flexible chloroplast-mitochondrion interactions able to overcome lesions in energy metabolism.

We have investigated the effect of colchicine, a disrupting agent of the tubulin cytoskeleton, on chlorophyll fluorescence parameters, the Hill reaction, noncyclic photophosphorylation, and the lipid peroxidation reaction in Solanum tuberosum grown in soil in a greenhouse environment. The destruction of microtubules caused an increase in the content of lipid fatty acid hydroperoxides, the primary product of lipid peroxidation, and led to changes in fluorescence parameters: F0 increased, Fm and the maximum quantum efficiency of PSII (Fv/Fm) decreased, and the dissipation of electronic excitation energy as heat increased. Simultaneously, it was found that the Hill reaction rate and the intensity of the process of noncyclic photophosphorylation decreased. The results obtained in this work are discussed in view of the destruction of the integrity of the chloroplast membrane and changes in chlorophyll fluorescence parameters due to colchicine application, as well as in light of our previously obtained data on the change in the content of phytohormones and their concentration ratios in potato leaves when microtubules are destroyed.

Lead (Pb) is an important pollutant of worldwide concern with respect to extensive pollution sources and highly toxic effect. Flavonol can improve plant resistance to abiotic stress and is also responsible for the alleviating effect under Pb stress. The relationship between Pb stress and flavonol and the knowledge about the mechanisms of flavonol function are very limited. Pb affected the energy metabolism process and, thus, inhibited plant growth and development. Flavonol accumulation controlled by FLS1 (flavonol synthase) could alleviate the toxic effect. Importantly, nes (mutant of NES that allows FLS1 to enter the nucleus expression) showed better growth status and lighter oxidative damage than NES (N-terminal nucleus exclusion signal peptide prevents FLS1 from entering the nucleus expression), which indicated that nucleus flavonol synthesized by nucleus FLS1 plays a key role in plant resistance to Pb stress. Although FLS1 signals were detected in the cell membrane, cytoplasm, and nucleus, membrane flavonol, cytoplasm flavonol, and nucleus flavonol were not exercising their function in the corresponding position. The expression of nucleus FLS1 intervened in the total content and composition of flavonol. The results also revealed that nucleus flavonol could regulate the ascorbate metabolism for alleviating the damage on the chloroplast, thus maintaining the photophosphorylation pathway. Our findings provided new insights for the molecular basis of Pb tolerance and response mechanism of the plant.

New and enhanced functions were potentially imparted to the plant organelles after interaction with nanoparticles. In this study, we found that ∼ 44% and ∼ 29% of the accumulated graphene in the rice leaves passively transported to the chloroplasts and thylakoid, respectively, significantly enhanced the fluorescence intensity of chloroplasts, and promoted about 2.4 times higher adenosine triphosphate production than that of controls. The enhancement of graphene on the photophosphorylation was ascribed to two reasons: One is that graphene facilitates the electron transfer process of photosystem II in thylakoid, and the other is that graphene protects the photosystem II against photo-bleaching by acting as a scavenger of reactive oxygen species. Overall, our work here confirmed that graphene translocating in the thylakoid promoted the photosynthetic activity of chloroplast in vivo and in vitro, providing new opportunities for designing biomimetic materials to enhance the solar energy conversion systems, especially for repairing or increasing the photosynthesis activity of the plants grown under stress environment.

To investigate the adaptive mechanism of wheat under high light, osmotic stress, and salt stress, redox regulation, and photosynthesis were compared. Under high light, the activities of antioxidant enzymes, except for catalase, significantly increased and then decreased after 1 and 3 h, respectively. Under osmotic stress, antioxidant enzyme activities significantly increased and subsequently declined. Except for superoxide dismutase, salt stress induced a significant increase in all the antioxidant enzyme activities. A significant decrease of D1 protein by high light and osmotic stress, strong photophosphorylation of D1 and D2 under high light and salt stress were observed, while all the stresses induced upregulation of PsbS protein. Eight stress-associated genes (TaMYB73, TaABC1, TaOPR1, TaASR1, TaWRKY44, TaWRKY2, TaWRKY19, and TaCIPK29) showed different expression levels under all the stresses. We conclude that the wheat plant adopted various strategies by regulating the antioxidant system, expression of stress-responsive genes, and photosystems under different abiotic stresses.

We studied bicarbonate-induced stimulation of photophosphorylation in thylakoids isolated from leaves of Arabidopsis thaliana plants. This stimulation was not observed in thylakoids of wild-type in the presence of mafenide, a soluble carbonic anhydrase inhibitor, and was absent in thylakoids of two mutant lines lacking the gene encoding alpha carbonic anhydrase 5 (αCA5). Using mass spectrometry, we revealed the presence of αCA5 in stromal thylakoid membranes of wild-type plants. A possible mechanism of the photophosphorylation stimulation by bicarbonate that involves αCA5 is proposed.

In this second half of our treatise on oxygenic photosynthesis, we provide support for the murburn model of the light reaction of photosynthesis and ratify key predictions made in the first part. Molecular docking and visualization of various ligands of quinones/quinols (and their derivatives) with PS II/Cytochrome b6f complexes did not support chartered 2e-transport role of quinols. A broad variety of herbicides did not show any affinity/binding-based rationales for inhibition of photosynthesis. We substantiate the proposal that disubstituted phenolics (perceived as protonophores/uncouplers or affinity-based inhibitors in the classical purview) serve as interfacial modulators of diffusible reactive (oxygen) species or DR(O)S. The DRS-based murburn model is evidenced by the identification of multiple ADP-binding sites on the extra-membraneous projection of protein complexes and structure/distribution of the photo/redox catalysts. With a panoramic comparison of the redox metabolic machinery across diverse organellar/cellular systems, we highlight the ubiquitous one-electron murburn facets (cofactors of porphyrin, flavin, FeS, other metal centers and photo/redox active pigments) that enable a facile harnessing of the utility of DRS. In the summative analyses, it is demonstrated that the murburn model of light reaction explains the structures of membrane supercomplexes recently observed in thylakoids and also accounts for several photodynamic experimental observations and evolutionary considerations. In toto, the work provides a new orientation and impetus to photosynthesis research. Communicated by Ramaswamy H. Sarma.

In this first part of our essay on oxygenic photosynthesis, we address the various aspects of classical and murburn explanations. We had recently pointed out that the classical explanations of- trans-membrane potential (TMP)-based chemiosmotic rotary ATP synthesis, quinone-cycle at cytochrome b6f, chartered electron transport by plastocyanin, and modality of light’s interaction with chloroplast pigments- are untenable. In lieu, we proposed a diffusible reactive (oxygen) species (DROS)-based murburn model. In continuum, herein, we assess the operational viability of the cyclic oxygenesis and electron transport chain (ETC) explanations for oxygenic photosynthesis, in the light of updated structural/mechanistic information. Further, thermodynamically validated murburn equations of photolysis-photophosphorylation (Pl-Pp) are provided, along with the rationale for organelle-homeostasis. We propose that the photo-excitation of various pigments leads to the formation of aquated electrons (eaq) and DROS in milieu, which are stabilized by a pool of redox-active elements within chloroplasts. Subsequently, the ‘eaq+DR(O)S’ pool is utilized stochastically via disordered/parallel reactions at the stacked thylakoid membrane interface. Effective charge separation by ‘photosystem switches’ enables delocalized oxygenesis, NAD(P) reduction and ADP phosphorylation. Heat/TMP/DROS generation is also an outcome of this process. Finally, we compare the murburn and classical models of Pl-Pp and delineate agendas for their ratification/falsification. Communicated by Ramaswamy H. Sarma Contemporary beliefs on oxygenic photosynthesis are critiqued.Murburn model is suggested as an alternative explanation.In the new model, diffusible reactive species are the main protagonists.All pigments are deemed photo-redox active in the new stochastic mechanism.NADPH synthesis occurs via simple electron transfers, not via elaborate ETC.Oxygenesis is delocalized and not just centered at Mn-Complex.Energetics of murburn proposal for photophosphorylation is provided.The proposal ushers in a paradigm shift in photosynthesis research. Contemporary beliefs on oxygenic photosynthesis are critiqued. Murburn model is suggested as an alternative explanation. In the new model, diffusible reactive species are the main protagonists. All pigments are deemed photo-redox active in the new stochastic mechanism. NADPH synthesis occurs via simple electron transfers, not via elaborate ETC. Oxygenesis is delocalized and not just centered at Mn-Complex. Energetics of murburn proposal for photophosphorylation is provided. The proposal ushers in a paradigm shift in photosynthesis research.

Textbooks of biochemistry will explain that the otherwise endergonic reactions of ATP synthesis can be driven by the exergonic reactions of respiratory electron transport, and that these two half-reactions are catalyzed by protein complexes embedded in the same, closed membrane. These views are correct. The textbooks also state that, according to the chemiosmotic coupling hypothesis, a (or the) kinetically and thermodynamically competent intermediate linking the two half-reactions is the electrochemical difference of protons that is in equilibrium with that between the two bulk phases that the coupling membrane serves to separate. This gradient consists of a membrane potential term Δψ and a pH gradient term ΔpH, and is known colloquially as the protonmotive force or pmf. Artificial imposition of a pmf can drive phosphorylation, but only if the pmf exceeds some 150-170mV; to achieve in vivo rates the imposed pmf must reach 200mV. The key question then is 'does the pmf generated by electron transport exceed 200mV, or even 170mV?' The possibly surprising answer, from a great many kinds of experiment and sources of evidence, including direct measurements with microelectrodes, indicates it that it does not. Observable pH changes driven by electron transport are real, and they control various processes; however, compensating ion movements restrict the Δψ component to low values. A protet-based model, that I outline here, can account for all the necessary observations, including all of those inconsistent with chemiosmotic coupling, and provides for a variety of testable hypotheses by which it might be refined.

The prevailing understanding on the light reaction of oxygenic photosynthesis (photolytic photophosphorylation & NADPH synthesis) considers the vast majority of the diverse pigments, chlorophyll binding proteins (CBPs) and light harvesting complexes (LHCs) as photon-energy relaying facets; only the chlorophyll a couplets at the reaction center of the two photosystems I & II are deemed to serve as photo-excitable electron emitters. Highlighting the historical perspectives involved, we present reasons why this conventional perception is unmet by theoretical foundations, unsupported by molecular awareness on the various pigments and unverified by physiological data available on chloroplasts. Further, we propose a simple diffusible reactive oxygen species (DROS)-based mechanism for correlating the functions of various light harvesting LHCs and CBPs with the reaction centers of Photosystems I & II. The projected hypothesis may also provide a new perspective to photoreception research.

Textbooks of biochemistry will explain that the otherwise endergonic reactions of ATP synthesis can be driven by the exergonic reactions of respiratory electron transport, and that these two half-reactions are catalyzed by protein complexes embedded in the same, closed membrane. These views are correct. The textbooks also state that, according to the chemiosmotic coupling hypothesis, a (or the) kinetically and thermodynamically competent intermediate linking the two half-reactions is the electrochemical difference of protons that is in equilibrium with that between the two bulk phases that the coupling membrane serves to separate. This gradient consists of a membrane potential term Δψ and a pH gradient term ΔpH, and is known colloquially as the protonmotive force or pmf. Artificial imposition of a pmf can drive phosphorylation, but only if the pmf exceeds some 150–170 mV; to achieve in vivo rates the imposed pmf must reach 200 mV. The key question then is ‘does the pmf generated by electron transport exceed 200 mV, or even 170 mV?’ The possibly surprising answer, from a great many kinds of experiment and sources of evidence, including direct measurements with microelectrodes, indicates it that it does not. Observable pH changes driven by electron transport are real, and they control various processes; however, compensating ion movements restrict the Δψ component to low values. A protet-based model, that I outline here, can account for all the necessary observations, including all of those inconsistent with chemiosmotic coupling, and provides for a variety of testable hypotheses by which it might be refined.

Phosphorus (P) is one of the most critical plant nutrients for all living organisms. Plants are known to be photosynthetic eukaryotes, and P plays significant role on photophosphorylation, respiration, and energy storage and transfer. It also regulates protein synthesis, cell division, and development of new tissue. Plants can take up the primary forms of phosphorus as H2PO4− and HPO42− (orthophosphates). In plants, this P concentration ranges is only 0.1–0.5% due to the challenges in the management of phosphorus. Although the content of total organic (P) and inorganic (Pi) form in the earth’s crust is high, the availability of orthophosphates is low and heterogeneous in almost all natural and agricultural ecosystems. In this review, we emphasize to gather the existing knowledge about P and propose how to increase the availability of orthophosphates by assimilation. Apart from this, several research findings including next-generation DNA and RNA sequencing coupled with other omic platforms have advanced considerably on the molecular basis of plant nutrition and how plants respond to nutritional stress. Moreover, we shed light on the factors involved on phosphorus uptake by plant, as well as critical responses under P starvation and metabolic activation to mitigate P deficiency.

Significant strides toward producing biochemical fuels have been achieved by mimicking natural oxidative and photosynthetic phosphorylation. Here, different from these strategies, we explore boric acid as a fuel for tuneable synthesis of energy-storing molecules in a cell-like supramolecular architecture. Specifically, a proton locked in boric acid is released in a modulated fashion by the choice of polyols. As a consequence, controlled proton gradients across the lipid membrane are established to drive ATP synthase embedded in the biomimetic architecture, which facilitates tuneable ATP production. This strategy paves a unique route to achieve highly efficient bioenergy conversion, holding broad applications in synthesis and devices that require biochemical fuels.

Techniques to probe molecular mechanistic events occurring at a single catalytic site of multi-subunit enzymes in real time are few and are still under development. Here time-resolved information is extracted from measurements of the extensive oxygen exchange that occurs at an intermediate stage of adenosine triphosphate (ATP) synthesis during photophosphorylation by chloroplast thylakoids. A stochastic process-based approach for modeling exchange reactions is formulated that provides a physical basis for the kinetic theory. Compatible with the assumptions made in such a model of randomness, the formulation is shown to lead to a Poisson-type theory that enables kinetic analysis of oxygen-exchange data and offers novel physical insights. Parameters such as the apparent rate constant of exchange and the average lifetime of the exchanging intermediates during the synthesis of ATP by the chloroplast F1FO-ATP synthase have been determined over a 5000-fold range of ADP concentration. Experimental isotopomer distributions of [18O]ATP at high (0.5 mM), intermediate (10 μM), and low (0.2 μM) ADP concentrations have been quantified and compared to expected distributions from the theory. The observed distributions are shown to closely match the predicted distributions. A wealth of novel mechanistic insights such as the number of sites/pathways of oxygen exchange, the order of substrate binding steps at the enzyme catalytic site, and regulation of the process of energy coupling have been deduced, and the results are interpreted with the help of available high-resolution X-ray structures. The various biological implications for models of energy coupling have been discussed. Permutation of oxygen ligands about the phosphorus center is proposed as a possible and general but not well-recognized mechanism for oxygen exchange that is consistent with the principal results of this work, and several suggestions for future research are offered.

Bark chloroplasts play important roles in carbon balancing by recycling internal stem CO2 into assimilated carbon. The photosynthetic response of bark chloroplasts to interior stem environments has been studied recently in woody plants. However, the molecular regulatory mechanisms underlying specific characteristics of bark photosynthesis remain unclear. To address this knowledge gap, differences in the structure, photosynthetic activity and protein expression profiles between bark and leaf chloroplasts were investigated in Salix matsudana in this study. Bark chloroplasts exhibited broader and lower grana stacks and higher levels of starch relative to leaf chloroplasts. Concomitantly, decreased oxygen evolution rates and decreased saturated radiation point were observed in bark chloroplasts. Furthermore, a total of 293 differentially expressed proteins (DEPs) were identified in bark and leaf chloroplast profile comparisons. These DEPs were significantly enriched in photosynthesis-related biological processes or Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways associated with photosynthesis. All 116 DEPs within the KEGG pathways associated with photosynthesis light reactions were downregulated in bark chloroplasts, including key proteins responsible for chlorophyll synthesis, light energy harvesting, nonphotochemical quenching, linear electron transport and photophosphorylation. Interestingly, seven upregulated proteins involved in dark reactions were identified in bark chloroplasts that comprised two kinds of malic enzymes typical of C4-type photosynthesis. These results provide comprehensive proteomic evidence to understand the low photochemical capability of bark chloroplasts and suggest that bark chloroplasts might fix CO2 derived from malate decarboxylation.

The construction of energetically autonomous artificial protocells is one of the most urgent and challenging requirements in bottom-up synthetic biology. Here we show a hybrid multi-compartment approach to build Artificial Simplified-Autotroph Protocells (ASAPs) in an effective manner. Chromatophores obtained fromRhodobacter sphaeroidesaccomplish the photophosphorylation of ADP to ATP functioning as nanosized photosynthetic organellae when encapsulated inside artificial giant phospholipid vesicles. Under continuous illumination chromatophores produce ATP that in turn sustains the transcription of a DNA gene by T7 RNA polymerase inside ASAPs. Cryo-EM and time-resolved spectroscopy were used for characterizing the chromatophore morphology and the orientation of the photophosphorylation proteins, which allow high ATP production rates (up to ~100 ATP/s per ATP synthase). mRNA biosynthesis inside individual vesicles has been determined by confocal microscopy. The hybrid multi-compartment approach here proposed appears at the same time convenient and effective, and thus very promising for the construction of full-fledged artificial protocells.

Plant cell produces a wide range of chemical compounds needed for its survival. Mostly secondary metabolite and phytochemicals including neurotransmitters are essential for the reallocation of resources in plants in response to changing environmental factors. Among them, dopamine which is a catecholamine neurotransmitter is found in plants as well as in animals. Many plants species of different families were reported to contain significant amounts of dopamine. It mediates many physiological processes in plants. However, the role of dopamine in plants is poorly documented. They are involved in much aspect of growth, development and their synthesis is regulated by stress condition. Studies have addressed the effect of dopamine on plants as allelochemical that provides defence against herbivore, processes such as nitrogen fixation, flowering and prevention against IAA oxidation, intercellular regulation of ion permeability and photophosphorylation of chloroplast. It has been proposed to be a precursor for various alkaloids benzylisoquinolines like papaverine and morphine or of the hallucinogenic alkaloid. In this chapter current knowledge on role of dopamine in plants are documented. Dopamine, noradrenaline and adrenaline were shown to participate in intercellular regulation of ion permeability and photophosphorylation of chloroplasts. Dopamine is involved in many functions like precursor for various alkaloids, antioxidative, sugar metabolism and coordinates with phytohormones to affect plant growth. In this chapter, current knowledge on role of dopamine in plants is documented.

Filamentous anoxygenic photosynthetic bacteria grow by photosynthesis and aerobic respiration. The present study investigated the effects of light and O2 on bacteriochlorophyll contents and the transcription levels of photosynthesis-related genes in Chloroflexus aurantiacus J-10-fl T. Under aerobic conditions, C. aurantiacus produced marked amounts of bacteriochlorophylls in the presence of light, although their production was strongly suppressed in the dark. The transcription levels of genes related to the synthesis of bacteriochlorophylls, photosystems, and chlorosomes: bchM, bchU, pufL, pufBA, and csmM, were markedly increased by illumination. These results suggest that C. aurantiacus continuously synthesizes ATP by photophosphorylation even in the presence of O2.

Uncoupling of photophosphorylation appears to have positive effect on lipid production of microalgae, however, underlying mechanisms involved in the effect are still unresolved. In this study, an uncoupler of photophosphorylation, carbonyl cyanide m-chlorophenyl hydrazone (CCCP), was used for the promotion of microalgal lipid accumulation. The results indicated that addition of CCCP was able to enhance the lipid productions of all tested species of Chlorella, especially when cultivated under mixotrophic condition. Based on the transcriptome and functional gene expression analyses, the functional genes involving in photosynthetic electron transport (PET), fatty acids synthesis, tricarboxylic acid (TCA) cycle, glycolysis and pentose phosphate (PP) pathway were found to be up-regulated while the genes participating in photosystem II, ATP synthesis during photosynthesis and calvin cycle were to be down-regulated by the presence of CCCP. According to these observations, the mechanism of CCCP to the promotion of lipid synthesis probably through channeling the NAD(P)H metabolic fluxes from carbon fixation towards fatty acid biosynthesis and lipid production, which was accomplished by (1) down-regulation of ribulose-1,5-bisphosphate carboxylase/oxygenase genes that involving in CO2 fixation via calvin cycle to reduce the NADPH consumption; (2) up-regulation of genes involved in TCA cycle and PP pathway to produce more NAD(P)H. The results of this study provide a new method to promote microalgal lipid production.

The gene cycA encodes a periplasmic protein, cytochrome c2 (cyt c2), which dominates electron transfer from the membrane-bound ubiquinol: cyt c2 oxidoreductase (cyt bc1) to the photosynthetic reaction center, contributing to the production of transmembrane proton potential and then the synthesis of ATP. For photosynthetic bacteria, the total energy supply for light anaerobic growth and hydrogen production comes from photophosphorylation. As a result, the key protein encoding gene plays an important role in hydrogen production. To figure out the specific effect of cycA expression level on H2 production ability of Rhodobacter sphaeroides HY01, cycA-expression plasmids derived from pRK415 and pBBR1MCS-2 were constructed and then crossed into the parent strain R. sphaeroides HY01 for H2 production test. And further verification by RT-PCR suggested that there was about 20% enhancement of cycA expression level by pBBR1MCS-2 where the H2 production performance of corresponding strain was improved by 6–8% compared with blank control. In contrast, cycA expression level was about 3.4 folds by vector pRK415 compared with control strain, but corresponding strains showed slightly depressed H2 production performance. Besides, the mutant XJ01 with cycA gene overexpressing by 70% in the genome of HY01(hupSL:cycA) also showed positive effect on hydrogen production performance. The results demonstrated that slightly overexpression of cycA could enhance the hydrogen production rate, but too much higher level of cycA-expression could show negative effect on H2 production performance of R. sphaeroides HY01.

A natural-artificial hybrid system was constructed to enhance photophosphorylation. The system comprises chloroplasts modified with optically matched quantum dots (chloroplast-QD) with a large Stokes shift. The QDs possess a unique optical property and transform ultraviolet light into available and highly effective red light for use by chloroplasts. This favorable feature enables photosystem II contained within the hybrid system to split more water and produce more protons than chloroplasts would otherwise do on their own. Consequently, a larger proton gradient is generated and photophosphorylation is improved. At optimal efficiency activity increased by up to 2.3 times compared to pristine chloroplasts. Importantly, the degree of overlap between emission of the QDs and absorption of chloroplasts exerts a strong influence on the photophosphorylation efficiency. The chloroplast-QD hybrid presents an efficient solar energy conversion route, which involves a rational combination of a natural system and an artificial light-harvesting nanomaterial.

Under optimal conditions, most of the light energy is used to drive electron transport. However, when the light energy exceeds the capacity of photosynthesis, the overall photosynthetic efficiency drops down. The present study investigated the effects of high light on rice photooxidation-prone mutant 812HS, characterized by a mutation of leaf photooxidation 1 gene, and its wild type 812S under field conditions. Our results showed no significant difference between 812HS and 812S before exposure to high sunlight. However, during exposure to high light, shoot tips of 812HS turned yellow and their chlorophyll (Chl) content decreased. Transmission electron microscopy showed that photooxidation resulted in significant damage of chloroplast ultrastructure. It was confirmed also by inhibited photophosphorylation and reduced ATP content. The decreased coupling factor of ATP, Ca2+-ATPase and Mg2+-ATPase activities also verified these results. Further, significantly enhanced activities of antioxidative enzymes were observed during photooxidation. Malondialdehyde, hydrogen peroxide, and the superoxide generation rates also increased. Chl a fluorescence analysis found that the performance index and maximum quantum yield of PSII declined on August 4, 20 days after high-light treatment. Net photosynthetic rate also decreased and substomatal CO2 concentration increased in 812HS at the same time. In conclusion, our findings indicated that excessive energy triggered the production of toxic reactive oxygen species and promoted lipid peroxidation in 812HS plants, causing severe damage to cell membranes, degradation of photosynthetic pigments and proteins, and ultimately inhibition of photosynthesis.

The initial product of photosynthesis is NADPH (dihydronicotinamide adenine dinucleotide phosphate), which is produced from the oxidized form (NADP+) by reduction with two electrons and one proton released from Photosystem I (PSI) via ferredoxin. The proton gradient generated across the thylakoid membrane produces a proton-motive force, which is utilized to synthesize ATP by the use of ATP synthase. NADPH is used as a hydride source in the Calvin–Benson cycle to produce sugars by photosynthesis. In addition to NADP+, PSI can reduce O2 by two electrons with two protons to produce hydrogen peroxide (H2O2), which can be used as a fuel in H2O2 fuel cells. This Minireview focuses on artificial photosynthetic systems to produce the products of natural photosynthesis, such as ATP, NAD(P)H and H2O2 from NAD+ and O2 with water using solar energy, respectively. ATP was produced by use of an artificial photosynthetic membrane, composed of a photosynthetic reaction center mimic that pumps protons into the interior of the liposome, where F-type ATP synthase was incorporated. Solar-driven catalytic water splitting produces hydrogen, which can reduce NAD+ to NADH with an iridium complex catalyst in a slightly alkaline solution at room temperature. H2O2 has been produced by the combination of four-electron oxidation of H2O with four protons to evolve O2 and two-electron/two-proton reduction of O2 under sun-light irradiation. H2O2 can also be produced by direct reaction of H2 and O2 by the combination of an iridium complex catalyst and flavin coenzyme.

Fo·F1H+-ATPase/synthase in coupled plasma membrane vesicles of Paracoccus denitrificans catalyzes ATP hydrolysis and/or ATP synthesis with comparable enzyme turnover. Significant difference in pH-profile of these alternative activities is seen: decreasing pH from 8.0 to 7.0 results in reversible inhibition of hydrolytic activity, whereas ATP synthesis activity is not changed. The inhibition of ATPase activity upon acidification results from neither change in ADP(Mg2+)-induced deactivation nor the energy-dependent enzyme activation. Vmax, not apparent KmATP is affected by lowering the pH. Venturicidin noncompetitively inhibits ATP synthesis and coupled ATP hydrolysis, showing significant difference in the affinity to its inhibitory site depending on the direction of the catalysis. This difference cannot be attributed to variations of the substrate-enzyme intermediates for steady-state forward and back reactions or to possible equilibrium between ATP hydrolase and ATP synthase Fo·F1 modes of the opposite directions of catalysis. The data are interpreted as to suggest that distinct non-equilibrated molecular isoforms of Fo·F1 ATP synthase and ATP hydrolase exist in coupled energy-transducing membranes.

Molecule assembly and functionalization of protocells have achieved a great success. However, the yield efficiency of photophosphorylation in the present cell-like systems is limited. Herein, inspired by natural photobacteria, we construct a protocell membrane reconstituting motor protein for highly efficient light-mediated adenosine triphosphate (ATP) synthesis through a layer-by-layer technique. The assembled membrane, compartmentally integrating photoacid generator, proton conductor, and ATP synthase, possesses excellent transparency, fast proton production, and quick proton transportation. Remarkably, these favorable features permit the formation of a large proton gradient in a confined region to drive ATP synthase to produce ATP with high efficiency (873 ATP s–1). It is the highest among the existing artificial photophosphorylation systems. Such a biomimetic system provides a bioenergy-supplying scenario for early photosynthetic life and holds promise in remotely controlled ATP-consumed biosensors, b...

Enhancing solar energy conversion efficiency is very important for developing renewable energy, protecting the environment, and producing agricultural products. Efficient enhancement of photophosphorylation is demonstrated by coupling artificial photoacid generators (PAGs) with chloroplasts. The encapsulation of small molecular long-lived PAGs in the thylakoid lumen is improved greatly by ultrasonication. Under visible-light irradiation, a fast intramolecular photoreaction of the PAG occurs and produces many protons, remarkably enhancing the proton gradient in situ. Consequently, compared to pure chloroplasts, the assembled natural-artificial hybrid demonstrates approximately 3.9 times greater adenosine triphosphate (ATP) production. This work will provide new opportunities for constructing enhanced solar energy conversion systems.

Cyclic electron flow around photosystem I (CEF) is critical for balancing the photosynthetic energy budget of the chloroplast by generating ATP without net production of NADPH. We demonstrate that the chloroplast NADPH dehydrogenase complex, a homolog to respiratory Complex I, pumps approximately two protons from the chloroplast stroma to the lumen per electron transferred from ferredoxin to plastoquinone, effectively increasing the efficiency of ATP production via CEF by 2-fold compared with CEF pathways involving non-proton-pumping plastoquinone reductases. By virtue of this proton-pumping stoichiometry, we hypothesize that NADPH dehydrogenase not only efficiently contributes to ATP production but operates near thermodynamic reversibility, with potentially important consequences for remediating mismatches in the thylakoid energy budget.

Theories of biological energy coupling in oxidative phosphorylation (OX PHOS) and photophosphorylation (PHOTO PHOS) are reviewed and applied to ATP synthesis by an experimental system containing purified ATP synthase reconstituted into liposomes. The theories are critically evaluated from the standpoint of the principle of electrical neutrality. It is shown that the obligatory requirement to maintain overall electroneutrality of bulk aqueous phases imposes strong constraints on possible theories of energy coupling and molecular mechanisms of ATP synthesis. Mitchell's chemiosmotic theory is found to violate the electroneutrality of bulk aqueous phases and is shown to be untenable on these grounds. Purely electroneutral mechanisms or mechanisms where the anion/countercation gradient is dissipated or simply flows through the lipid bilayer are also shown to be inadequate. A dynamically electrogenic but overall electroneutral mode of ion transport postulated by Nath's torsional mechanism of energy transduction and ATP synthesis is shown to be consistent both with the experimental findings and the principle of electrical neutrality. It is concluded that the ATP synthase functions as a proton-dicarboxylic acid anion cotransporter in OX PHOS or PHOTO PHOS. A logical chemical explanation for the selection of dicarboxylic acids as intermediates in OX PHOS and PHOTO PHOS is suggested based on the pioneering classical thermodynamic work of Christensen, Izatt, and Hansen. The nonequilibrium thermodynamic consequences for theories in which the protons originate from water vis-a-vis weak organic acids are compared and contrasted, and several new mechanistic and thermodynamic insights into biological energy transduction by ATP synthase are offered. These considerations make the new theory of energy coupling more complete, and lead to a deeper understanding of the molecular mechanism of ATP synthesis.

As the chief energy source of eukaryotic cells, it is important to determine the thermodynamic efficiency of ATP synthesis in oxidative phosphorylation (OX PHOS). Previous estimates of the thermodynamic efficiency of this vital process have ranged from Lehninger's original back-of-the-envelope calculation of 38% to the often quoted value of 55-60% in current textbooks of biochemistry, to high values of 90% from recent information theoretic considerations, and reports of realizations of close to ideal 100% efficiencies by single molecule experiments. Hence this problem has been reinvestigated from first principles. The overall thermodynamic efficiency of ATP synthesis in the mitochondrial energy transduction OX PHOS process has been found to lie between 40 and 41% from four different approaches based on a) estimation using structural and biochemical data, b) fundamental nonequilibrium thermodynamic analysis, c) novel insights arising from Nath's torsional mechanism of energy transduction and ATP synthesis, and d) the overall balance of cellular energetics. The torsional mechanism also offers an explanation for the observation of a thermodynamic efficiency approaching 100% in some experiments. Applications of the unique, molecular machine mode of functioning of F1FO-ATP synthase involving direct inter-conversion of chemical and mechanical energies in the design and fabrication of novel, man-made mechanochemical devices have been envisaged, and some new ways to exorcise Maxwell's demon have been proposed. It is hoped that analysis of the fundamental problem of energy transduction in OX PHOS from a fresh perspective will catalyze new avenues of research in this interdisciplinary field.

The effect of the rate of ADP supply as a feedback signal on the rate of ATP synthesis in chloroplasts has been analyzed on the basis of literature data and our research results. Experimental data are discussed in the context of the diffusion controlled mode of photophosphorylation.

CO(2) concentration ([CO(2)]) in a greenhouse may be a limiting factor for plant growth. Current greenhouse CO(2) control strategy usually depends on expert experience, which may control [CO(2)] in a moderate range but cannot make it optimal due to lack of considering plant photochemistry reactions. A state‐space kinetic model structure covering major photosynthetic reactions as affected by CO(2) is useful for [CO(2)] control strategy development in a greenhouse because modern control theories are usually based on state‐space models. In this work, a state‐space kinetic model structure for photosynthesis was built, which describes the major reaction cascades of photophosphorylation, Calvin cycle, and biophysical processes such as CO(2) transport through the stomata under moderate [CO(2)] range without considering photorespiration. Simulations were performed with a large range of model parameters to demonstrate the effect of [CO(2)] on stable sugar production and the flexibilities of the developed model structure. The results clearly show whether increasing of CO(2) will lead to more production of sugar or not in different scenarios. The model structure may be extended to cover other photosynthetic influence factors such as temperature by using the well‐known Arrhenius equation.

This chapter focuses on renewable power generation approaches based on the coupling of photosynthetic bioreactors. In PhFCs, oxidation of organic compounds results in electrons production by photosynthetic bacteria. PhFC research has allowed the generation of a wide variety of different system configurations, the use of photosynthetic mechanism, and respective organisms. Oxygenic photosynthetic species commence charge separation results in delivering electrons and protons in a photophosphorylation cascade. Photosynthetic microbial fuel cell research started with cyanobacterial species of Synechocystis and Anabaena by documenting the increment in power output in light and decrement in power during the dark. Photosynthetic organisms use carbon dioxide as carbon source, and photosynthetic reactions involve the reduction of this molecule. Oxygen generation in photosynthetic reactions represents an interesting characteristic in the cathode process, because mechanic aeration requires vast quantities of energy. Illumination is a salient feature for growth of photosynthetic microorganisms.

Prototypes of natural biosystems provide opportunities for artificial biomimetic systems to break the limits of natural reactions and achieve output control. However, mimicking unique natural structures and ingenious functions remains a challenge. Now, multiple biochemical reactions were integrated into artificially designed compartments via molecular assembly. First, multicompartmental silica nanoparticles with hierarchical structures that mimic the chloroplasts were obtained by a templated synthesis. Then, photoacid generators and ATPase-liposomes were assembled inside and outside of silica compartments, respectively. Upon light illumination, protons produced by a photoacid generator in the confined space can drive the liposome-embedded enzyme ATPase towards ATP synthesis, which mimics the photophosphorylation process in vitro. The method enables fabrication of bioinspired nanoreactors for photobiocatalysis and provides insight for understanding sophisticated biochemical reactions.

Gemmatimonas phototrophica is, so far, the only described phototrophic species of the bacterial phylum Gemmatimonadetes. Its cells contain a unique type of photosynthetic complex with the reaction center surrounded by a double ring antenna, however they can also grow in the dark using organic carbon substrates. Its photosynthesis genes were received via horizontal gene transfer from Proteobacteria. This raises two questions; how the horizontally transferred photosynthesis apparatus has integrated into the cellular machinery, and how much light-derived energy actually contributes to the cellular metabolism? To address these points, the photosynthetic reactions were studied on several levels, from photophysics of the reaction center to cellular growth. Flash photolysis measurements and bacteriochlorophyll fluorescence kinetic measurements documented the presence of fully functional type-2 reaction centers with a large light harvesting antenna. When illuminated, the bacterial cells reduced their respiration rate by 58 ± 5%, revealing that oxidative phosphorylation was replaced by photophosphorylation. Moreover, illumination also more than doubled the assimilation rates of glucose, a sugar that is mostly used for respiration. Finally, light increased the growth rates of Gemmatimonas phototrophica colonies on agar plates. All the presented data provide evidence that photosynthetic complexes are fully integrated into cellular metabolism of Gemmatimonas phototrophica, and are able to provide a substantial amount of energy for its metabolism and growth.

The crystal structure has been determined of the F1-catalytic domain of the F-ATPase from Caldalkalibacillus thermarum, which hydrolyzes adenosine triphosphate (ATP) poorly. It is very similar to those of active mitochondrial and bacterial F1-ATPases. In the F-ATPase from Geobacillus stearothermophilus, conformational changes in the ε-subunit are influenced by intracellular ATP concentration and membrane potential. When ATP is plentiful, the ε-subunit assumes a "down" state, with an ATP molecule bound to its two C-terminal α-helices; when ATP is scarce, the α-helices are proposed to inhibit ATP hydrolysis by assuming an "up" state, where the α-helices, devoid of ATP, enter the α3β3-catalytic region. However, in the Escherichia coli enzyme, there is no evidence that such ATP binding to the ε-subunit is mechanistically important for modulating the enzyme's hydrolytic activity. In the structure of the F1-ATPase from C. thermarum, ATP and a magnesium ion are bound to the α-helices in the down state. In a form with a mutated ε-subunit unable to bind ATP, the enzyme remains inactive and the ε-subunit is down. Therefore, neither the γ-subunit nor the regulatory ATP bound to the ε-subunit is involved in the inhibitory mechanism of this particular enzyme. The structure of the α3β3-catalytic domain is likewise closely similar to those of active F1-ATPases. However, although the βE-catalytic site is in the usual "open" conformation, it is occupied by the unique combination of an ADP molecule with no magnesium ion and a phosphate ion. These bound hydrolytic products are likely to be the basis of inhibition of ATP hydrolysis.

Nitrogenase is an ATP-requiring enzyme capable of carrying out multielectron reductions of inert molecules. A purified remodeled nitrogenase containing two amino acid substitutions near the site of its FeMo cofactor was recently described as having the capacity to reduce carbon dioxide (CO2) to methane (CH4). Here, we developed the anoxygenic phototroph, Rhodopseudomonas palustris, as a biocatalyst capable of light-driven CO2 reduction to CH4 in vivo using this remodeled nitrogenase. Conversion of CO2 to CH4 by R. palustris required constitutive expression of nitrogenase, which was achieved by using a variant of the transcription factor NifA that is able to activate expression of nitrogenase under all growth conditions. Also, light was required for generation of ATP by cyclic photophosphorylation. CH4 production by R. palustris could be controlled by manipulating the distribution of electrons and energy available to nitrogenase. This work shows the feasibility of using microbes to generate hydrocarbons from CO2 in one enzymatic step using light energy.

Thylakoid membrane-localized chloroplast ATP synthases use the proton motive force generated by photosynthetic electron transport to produce ATP from ADP. Although it is well known that the chloroplast ATP synthase is composed of more than 20 proteins with α3β3γ1ε1δ1I1II1III14IV1 stoichiometry, its biogenesis process is currently unclear. To unravel the molecular mechanisms underlying the biogenesis of chloroplast ATP synthase, we performed extensive screening for isolating ATP synthase mutants in Arabidopsis (Arabidopsis thaliana). In the recently identified bfa3 (biogenesis factors required for ATP synthase 3) mutant, the levels of chloroplast ATP synthase subunits were reduced to approximately 25% of wild-type levels. In vivo labeling analysis showed that assembly of the CF1 component of chloroplast ATP synthase was less efficient in bfa3 than in the wild type, indicating that BFA3 is required for CF1 assembly. BFA3 encodes a chloroplast stromal protein that is conserved in higher plants, green algae, and a few species of other eukaryotic algae, and specifically interacts with the CF1β subunit. The BFA3 binding site was mapped to a region in the catalytic site of CF1β. Several residues highly conserved in eukaryotic CF1β are crucial for the BFA3–CF1β interaction, suggesting a coevolutionary relationship between BFA3 and CF1β. BFA3 appears to function as a molecular chaperone that transiently associates with unassembled CF1β at its catalytic site and facilitates subsequent association with CF1α during assembly of the CF1 subcomplex of chloroplast ATP synthase.

Murburn concept is a redox mechanistic scheme involving interactive equilibriums of discretized or organized protein/substrate molecules, unbound ions and radicals (or reactive species); which may afford selective/specific electron transfers, particularly at phospholipid interfaces. Earlier, we have applied murburn concept to provide thermodynamically and kinetically viable explana-tions for various physiological/bioenergetic routines like xenobiotic metabolism, unusual dose responses, aerobic respiration, thermogenesis, homeostasis, trans-membrane potential, oxygenic photosynthesis, etc. While proposing the murburn model for photophosphorylation, we had projected that the murburn mechanism could also be relevant for photoreception physiology. Herein, we expand on this aspect and present the basic scheme and evidence in support of the murburn model of photorecep-tion, with retinal/opsin as the salient photon-impingement response-transducing element. In alignment with our earlier murburn schemes, we propose that diffusible reactive oxygen species (DROS, as exemplified by superoxide, which is currently deemed a toxic product of all-trans retinal and NADPH oxidase interactions) is produced in rod/cone cells upon photoactivation and it plays a crucial role in the visual cycle. This is supported by several facts: (i) Layers of photoreceptive neural cells precede the rod/cone cells (with respect to the presentation to oncoming light ray/photon), (ii) There exists high oxygen demand in the retina, (iii) Copious DROS are detected in functional retina, (iv) NAD(P)H/reductase is involved in the cycle, and (v) Events occur at sub-micrometer dimensioned phospholipid disks stacked to stabilize DROS and minimize free protons (quite like the thylakoids that harbor carotenoids in chloroplasts and cyanobacteria). In the new scheme, photo-electric activation leads to charge sepa-ration and hyperpolarization in rod/cone cells due to negative charge build-up. This electro-chemical signaling serves as the front-runner to trigger an action potential relay along a neuron and the superoxide mediated phosphorylation of GDP bound to transducin serves as the initiator of signal transduction cascade. The newly proposed scheme allows a simple electrical connec-tivity of the retina-photoreceptors with the brain via the optic nerve, is anatomically correlated with the structure and resolution of the retina, and is kinetically viable.

In a recent publication, Manoj raises criticisms against consensus views on the ATP synthase. The radical statements and assertions are shown to contradict a vast body of available knowledge that includes i) pioneering single-molecule biochemical and biophysical studies from the respected experimental groups of Kinosita, Yoshida, Noji, Borsch, Dunn, Graber, Frasch, and Dimroth etc., ii) state-of-the-art X-ray and EM/cryo-EM structural information garnered over the decades by the expert groups of Leslie-Walker, Kuhlbrandt, Mueller, Meier, Rubinstein, Sazanov, Duncan, and Pedersen on ATP synthase, iii) the pioneering energy-based computer simulations of Warshel, and iv) the novel theoretical and experimental works of Nath. Valid objections against Mitchell's chemiosmotic theory and Boyer's binding change mechanism put forth by Manoj have been addressed satisfactorily by Nath's torsional mechanism of ATP synthesis and two-ion theory of energy coupling and published 10 to 20 years ago, but these papers are not cited by him. This communication shows conclusively and in great detail that none of his objections apply to Nath's mechanism/theory. Nath's theory is further consolidated based on its previous predictive record, its consistency with biochemical evidence, its unified nature, its application to other related energy transductions and to disease, and finally its ability to guide the design of new experiments. Some constructive suggestions for high-resolution structural experiments that have the power to delve into the heart of the matter and throw unprecedented light on the nature of coupled ion translocation in the membrane-bound FO portion of F1FO-ATP synthase are made.

At present, photophosphorylation in natural or artificial systems is accomplished by the production of protons or their pumping across the biomembranes. Herein, different from this strategy above, we demonstrate a designed system which can effectively enhance photophosphorylation by photo-induced proton-scavenging through molecular assembly. Upon the introduction of photobase generators, a (photo-) chemical reaction occurs to produce hydroxyl ions. Accompanying the further extramembranous acid-base neutralization reaction, an outbound flow of protons is generated to drive the reconstituted adenosine triphosphate (ATP) synthase to produce ATP. That is, contrary to biochemistry, the proton gradient to drive photophosphorylation derives from the scavenging of protons present in the external medium by hydroxyl ions, produced by the partially photo-induced splitting of photobase generator. Such assembled system holds great potential in ATP-consuming bioapplications.

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.