Chloroplast Transport Research Articles

Electron and proton transport in chloroplasts of pea plants after night exposures to chilling temperatures

Electron and proton transport in chloroplasts of pea plants after night exposures to chilling temperatures

A rice chloroplast‐localized ABC transporter ARG1 modulates cobalt and nickel homeostasis and contributes to photosynthetic capacity

Transport and homeostasis of transition metals in chloroplasts, which are accurately regulated to ensure supply and to prevent toxicity induced by these metals, are thus crucial for chloroplast function and photosynthetic performance. However, the mechanisms that maintain the balance of transition metals in chloroplasts remain largely unknown. We have characterized an albino-revertible green 1 (arg1) rice mutant. ARG1 encodes an evolutionarily conserved protein belonging to the ATP-binding cassette (ABC) transporter family. Protoplast transfection and immunogold-labelling assays showed that ARG1 is localized in the envelopes and thylakoid membranes of chloroplasts. Measurements of metal contents, metal transport, physiological and transcriptome changes revealed that ARG1 modulates cobalt (Co) and nickel (Ni) transport and homeostasis in chloroplasts to prevent excessive Co and Ni from competing with essential metal cofactors in chlorophyll and metal-binding proteins acting in photosynthesis. Natural allelic variation in ARG1 between indica and temperate japonica subspecies of rice is coupled with their different capabilities for Co transport and Co content within chloroplasts. This variation underpins the different photosynthetic capabilities in these subspecies. Our findings link the function of the ARG1 transporter to photosynthesis, and potentially facilitate breeding of rice cultivars with improved Co homeostasis and consequently improved photosynthetic performance.

Phylogeny, structural diversity and genome-wide expression analysis of fibrillin family genes in rice

Fibrillins (FBNs) constitute a plastid-lipid-associated protein family that plays a role in chloroplast development, lipids metabolism and stress responses in plants. Until now, FBNs have been functionally characterized in stability of thylakoid and responses to the different stress stimuli. Consequently, phylogeny, domain composition and structural features of 121 FBNs family proteins from ten representative species have been identified. As results, phylogenetic analysis demonstrated that FBNs proteins were grouped into 24 clades and further subdivided into three groups, including terrestrial plant-specific, algae-specific, and intermediate group. These FBNs genes had different numbers of introns and exons but encoded the conserved N-terminal chloroplast transport peptide (CTP) domains and plastid lipid-associated protein (PAP) domains, which greatly contributed to the sub-functionalization and neo-functionalization. Meanwhile, the CTP domains of eleven OsFBN proteins except OsFBN8 could help them transport into chloroplasts. The PAP domains of OsFBN2 and OsFBN4 showed the in vitro specific binding activity to C12–C22 fatty acids that were affected by YxD motif. The qRT-PCR analysis showed that OsFBN genes were differentially induced by heat stress and cold stress in rice. Collectively, this study has provided the new insights into the evolution, structure, and functions of FBN gene family and will help to elucidate the molecular mechanisms of these proteins functioning in growth, development and adaptations in the global climate change.

PH-Dependent Regulation of Electron and Proton Transport in Chloroplasts In Situ and In Silico

The analysis of electron and proton transport in chloroplasts of higher plants has been carried out on the basis of a mathematical model that takes into account the pH-dependent regulation of electron transport and the operation of the ATP synthase. Numerical experiments aimed at simulation of these processes under pseudocyclic electron transport (water–water cycle) have shown good agreement with experimental data on the kinetics of electron transfer to photosystem 1 (PS1) in class B chloroplasts in metabolic states corresponding to high (state 3) and low (state 4) ATP synthase activity. The simulation of electron transport processes that took into account the Calvin–Benson cycle (CBC), cyclic electron transport around PS1, pH-dependent heat dissipation of energy in photosystem 2 (PS2), and nonphotochemical quenching (NPQ) made it possible to estimate the contribution of these factors to the kinetics of induction phenomena in chloroplasts in situ. It has been shown that the multiphase kinetics of the photooxidation of P700 (a primary electron donor in PS1) reflects the redistribution of electron flows between cyclic and non-cyclic electron transfer pathways, caused by the activation of CBC due to the alkalization of the stroma, as well as the change of the limiting stage in the electron transport chain, induced by a decrease in the intrathylakoid pH (pHin). The electron flux between PS2 and PS1 decelerates with pHin decrease, which may be caused by the reduced rate of plastoquinol oxidation and attenuated activity of PS2 due to NPQ.

Cloning and Expression Analysis of Chloroplast-targeted Ferredoxin-NADP+ Oxidoreductase Gene of Tea Plant (<i>Camellia sinensis</i>) cv.Huangjinya

The chloroplast-targeted ferredoxin-NADP + oxidoreductase (LFNR) is a hydrophilic flavin protein located at the end of the photosynthesis electron delivery chain in higher plants. It’s a hub for linking photosynthesis electronic transportation with chloroplast redox metabolism. In order to explore the relationship between LFNR gene and yellowing of ‘Huangjinya’controlled by light, we took separately one bud two leaves of ‘Huangjinya’ ‘Shuchazao’（CK） as the material to clone CsLFNR gene and then we obtained the sequence with a similarity of 100%, named CsLFNR1.1 (GenBank accession no. MT311318). Throw bioinformatics analysis, we know its cDNA gene length is 1095bp,coding 364 amino acids, The protein molecular weight is 40.623KDa, the theoretical isoelectric point is 8.86.CsLFNR1.1 is a alkaline protein without transmembrane structure and signal peptide, it has a chloroplast transport peptide(cTP), the secondary structure contains 23.35% alpha helix, 5.49% beta-corner, 28.85% extension chain and 42.31% irregular curling, It locates in the chloroplast. Through the Nucleotide BLAST, Protein BLAST and DNAMAN software, we found that C sLFNR1.1 and its translated amino acid sequences had 4 bases and 3 amino acid differences with NCBI ‘Shuchazao’ Gene CsLFNR1 (XM_028233617.1) and Protein (XP_028089418.1), the similarity reached 99.63% and 99.18%. CsLFNR1.1 and CsLFNR1 have small differences in the physical and chemical properties and secondary structure, the tertiary structure prediction template of them is consistent. In addition, they have the same conserved domain and active site. We took different shade ‘Huangjinya’ blades as the material for qRT-PCR, the result showed that the expression of CsLFNR1.1 gene response to the light intensity, its expression increased with the increase of light intensity. This study provides a theoretical basis and scientific basis for further exploring the role of CsLFNR1.1 gene in the light regulation process of the new shoots and leaves of ‘Huangjinya’.

Bioinformatics Prediction and Comparison of <i>Artocarpus heterophyllus</i> BRI1 Family Members

Full-length trantogenic sequencing (PRJNA579273) of jackfruit seedling stems and leaves was performed. On this basis, biological information analysis was performed on Jackfruit ( Artocarpus heterophyllus ) BR INSENSITIVE 1 (BRI1) family members AhBRI1 , AhBRL1 and AhBRL2 to translate genes into proteins. Using online analysis tools, jackfruit, Arabidopsis (Arabidopsis Thaliana), Sichuan mulberry (Morus notabilis) and Poplar (Populus trichocarpa) were used to analyze and obtain different physicochemical properties data and the secondary and tertiary structure of the protein. The bioinformatics prediction and comparison between the BRI1 protein families of different species were obtained. The results showed that the amino acid residues were 1 195, 1 170 and 985, and the theoretical isoelectric points were 6.32, 5.77 and 7.08. The protein was weakly acidic, hydrophilic and stable. There are secretory pathway signal peptides or chloroplast transport peptides with transmembrane structure. The main components of the secondary structure are irregular coil and -helix, and the tertiary structure is spiral tubular structure. This study provides a basis for further functional studies on members of the BRI1 protein family of jackfruit.

Electrochemistry of ring-substituted 1-hydroxynaphthalene-2-carboxanilides: Relation to structure and biological activity

Twenty-two novel antimycobacterial agents, 1-hydroxynaphthalene-2-carboxanilides, were studied by cyclic voltammetry on a glassy carbon electrode in a phosphate buffer pH 7.2 – dimethyl sulfoxide (DMSO) mixed medium (9:1; v/v). All compounds exhibited similar voltammetric behavior with one irreversible anodic signal in the range 100–300 mV corresponding to the oxidation of hydroxyl group on the naphthalene moiety. A shift of the oxidation potential was caused solely by electron donating or withdrawing effects of substituents and their position on the benzene moiety. Mechanism of oxidation in the studied medium was briefly outlined. Values of oxidation potentials exhibited very good linear correlation with calculated Hammett σ substituent constants. For all active compounds, a relationship between oxidation potentials and MIC or IC50 values obtained from in vitro screening was investigated in detail. Primary in vitro screening of synthesized compounds was previously performed against three species of Mycobacterium pathogens. Additionally, their activity related to the inhibition of photosynthetic electron transport (PET) in spinach chloroplasts was tested in previous publications. In vitro screening against Mycobacterium tuberculosis was performed here for the first time with 1-hydroxy-N-(3-trifluoromethylphenyl)naphthalene-2-carboxamide being the most effective (MIC = 11.7 μmol L−1). Furthermore, several other compounds showed higher antimycobacterial activity than the standard isoniazid. Relation of biological activities and oxidation potentials was successfully found in some cases; however, final correlations must also be considered with other physical and chemical factors contributing to the biological activity. Relation of structure, biological activity and electrochemical potential was also studied by cyclic voltammetry in cathodic area for three compounds containing reducible nitro moiety.

Prolonged oxygen depletion in microwounded cells of Chara corallina detected with novel oxygen nanosensors.

Primary physicochemical steps in microwounding of plants were investigated using electrochemical nano- and microprobes, with a focus on the role of oxygen in the wounding responses of individual plant cells. Electrochemical measurements of cell oxygen content were made with carbon-filled quartz micropipettes with platinum-coated tips (oxygen nanosensors). These novel platinum nanoelectrodes are useful for understanding cell oxygen metabolism and can be employed to study the redox biochemistry and biology of cells, tissues and organisms. We show here that microinjury of Chara corallina internodal cells with the tip of a glass micropipette is associated with a drastic decrease in oxygen concentration at the vicinity of the stimulation site. This decrease is reversible and lasts for up to 40 minutes. Membrane stretching, calcium influx, and cytoskeleton rearrangements were found to be essential for the localized oxygen depletion induced by cell wall microwounding. Inhibition of electron transport in chloroplasts or mitochondria did not affect the magnitude or timing of the observed response. In contrast, the inhibition of NADPH oxidase activity caused a significant reduction in the amplitude of the decrease in oxygen concentration. We suggest that the observed creation of localized anoxic conditions in response to cell wall puncture might be mediated by NADPH oxidase.

Overexpressing OsFBN1 enhances plastoglobule formation, reduces grain-filling percent and jasmonate levels under heat stress in rice

In higher plants, Fibrillins (FBNs) constitute a conserved plastid-lipid-associated (PAPs) protein family and modulate the metabolite transport and lipid metabolism in plastids of dicot species. However, FBNs have not functionally characterized in monocot species. In this study, the function of rice fibrillin 1 (OsFBN1) was investigated. The subcellular localization assay showed that the N-terminal chloroplast transport peptide (CTP) could facilitate the import of OsFBN1 into chloroplast. OsFBN1 specifically bound C18- and C20- fatty acids in vitro. Overexpressing OsFBN1 increased the tiller number but decreased the panicle length, grain-filling percent and JA levels compared to the wild type and RNAi silencing lines under heat stress. In addition, the overexpressing lines had more plastoglobules (PGs) than the wild type and RNAi silencing lines under both normal and heat stress conditions. Moreover, overexpressing OsFBN1 affected the transcription levels of OsAOS2 in JA synthesis, OsTHF1, OsABC1K7 and OsPsaE in thylakoid stability and photosynthesis, OsABC1-4 and OsSPS2 in ubiquinone-metabolism, OsHDR, OsDXR, and OsFPPS in isoprenoid metabolism. Collectively, these findings suggest the essential role of rice OsFBN1 in PG formation and lipid metabolism in chloroplasts, which coordinately regulate the growth and grain filling of the overexpressing lines under heat stress.

Essential and Detrimental - an Update on Intracellular Iron Trafficking and Homeostasis.

Chloroplasts, mitochondria and vacuoles represent characteristic organelles of the plant cell, with a predominant function in cellular metabolism. Chloroplasts are the site of photosynthesis and therefore basic and essential for photoautotrophic growth of plants. Mitochondria produce energy during respiration and vacuoles act as internal waste and storage compartments. Moreover, chloroplasts and mitochondria are sites for the biosynthesis of various compounds of primary and secondary metabolism. For photosynthesis and energy generation, the internal membranes of chloroplasts and mitochondria are equipped with electron transport chains. To perform proper electron transfer and several biosynthetic functions, both organelles contain transition metals and here iron is by far the most abundant. Although iron is thus essential for plant growth and development, it becomes toxic when present in excess and/or in its free, ionic form. The harmful effect of the latter is caused by the generation of oxidative stress. As a consequence, iron transport and homeostasis have to be tightly controlled during plant growth and development. In addition to the corresponding transport and homeostasis proteins, the vacuole plays an important role as an intracellular iron storage and release compartment at certain developmental stages. In this review, we will summarize current knowledge on iron transport and homeostasis in chloroplasts, mitochondria and vacuoles. In addition, we aim to integrate the physiological impact of intracellular iron homeostasis on cellular and developmental processes.

Electron transport pathways in isolated chromoplasts from Narcissus pseudonarcissus L.

During daffodil flower development, chloroplasts differentiate into photosynthetically inactive chromoplasts having lost functional photosynthetic reaction centers. Chromoplasts exhibit a respiratory activity reducing oxygen to water and generating ATP. Immunoblots revealed the presence of the plastid terminal oxidase (PTOX), the NAD(P)H dehydrogenase (NDH) complex, the cytochrome b6 f complex, ATP synthase and several isoforms of ferredoxin-NADP+ oxidoreductase (FNR), and ferredoxin (Fd). Fluorescence spectroscopy allowed the detection of chlorophyll a in the cytochrome b6 f complex. Here we characterize the electron transport pathway of chromorespiration by using specific inhibitors for the NDH complex, the cytochrome b6 f complex, FNR and redox-inactive Fd in which the iron was replaced by gallium. Our data suggest an electron flow via two separate pathways, both reducing plastoquinone (PQ) and using PTOX as oxidase. The first oxidizes NADPH via FNR, Fd and cytochrome bh of the cytochrome b6 f complex, and does not result in the pumping of protons across the membrane. In the second, electron transport takes place via the NDH complex using both NADH and NADPH as electron donor. FNR and Fd are not involved in this pathway. The NDH complex is responsible for the generation of the proton gradient. We propose a model for chromorespiration that may also be relevant for the understanding of chlororespiration and for the characterization of the electron input from Fd to the cytochrome b6 f complex during cyclic electron transport in chloroplasts.

Moss Kinesin-14 KCBP Accelerates Chromatid Motility in Anaphase.

KCBP is a microtubule (MT) minus-end-directed kinesin widely conserved in plants. It was shown in Arabidopsis that KCBP controls trichome cell shape by orchestrating MT and actin cytoskeletons using its tail and motor domains. In contrast, the KCBP knockout (KO) line in the moss Physcomitrella patens showed a defect in nuclear and organelle positioning in apical stem cells. Moss KCBP is postulated to transport the nucleus and chloroplast via direct binding to their membranes, since it binds to and transports liposomes composed of phospholipids in vitro. However, domains required for cargo transport in vivo have not been mapped. Here, we performed a structure-function analysis of moss KCBP. We found that the FERM domain in the tail region, which is known to bind to lipids as well as other proteins, is essential for both nuclear and chloroplast positioning, whereas the proximal MyTH4 domain plays a supporting role in chloroplast transport. After anaphase but prior to nuclear envelope re-formation, KCBP accumulates on the chromosomes, in particular at the centromeric region in a FERM-dependent manner. In the KCBP KO line, the rate of poleward chromosome movement in anaphase was reduced and lagging chromosomes occasionally appeared. These results suggest that KCBP binds to non-membranous naked chromosomes via an unidentified protein(s) for their transport. Finally, the liverwort orthologue of KCBP rescued the chromosome/chloroplast mis-positioning of the moss KCBP KO line, suggesting that the cargo transport function is conserved at least in bryophytes.Key words: kinesin, mitosis, chromosome segregation, kinetochore, dynein.

Hydrogen peroxide metabolism and functions in plants.

Contents Summary 1197 I. Introduction 1198 II. Measurement and imaging of H2 O2 1198 III. H2 O2 and O2·- toxicity 1199 IV. Production of H2 O2 : enzymes and subcellular locations 1200 V. H2 O2 transport 1205 VI. Control of H2 O2 concentration: how and where? 1205 VII. Metabolic functions of H2 O2 1207 VIII. H2 O2 signalling 1207 IX. Where next? 1209 Acknowledgements 1209 References 1209 SUMMARY: Hydrogen peroxide (H2 O2 ) is produced, via superoxide and superoxide dismutase, by electron transport in chloroplasts and mitochondria, plasma membrane NADPH oxidases, peroxisomal oxidases, type III peroxidases and other apoplastic oxidases. Intracellular transport is facilitated by aquaporins and H2 O2 is removed by catalase, peroxiredoxin, glutathione peroxidase-like enzymes and ascorbate peroxidase, all of which have cell compartment-specific isoforms. Apoplastic H2 O2 influences cell expansion, development and defence by its involvement in type III peroxidase-mediated polymer cross-linking, lignification and, possibly, cell expansion via H2 O2 -derived hydroxyl radicals. Excess H2 O2 triggers chloroplast and peroxisome autophagy and programmed cell death. The role of H2 O2 in signalling, for example during acclimation to stress and pathogen defence, has received much attention, but the signal transduction mechanisms are poorly defined. H2 O2 oxidizes specific cysteine residues of target proteins to the sulfenic acid form and, similar to other organisms, this modification could initiate thiol-based redox relays and modify target enzymes, receptor kinases and transcription factors. Quantification of the sources and sinks of H2 O2 is being improved by the spatial and temporal resolution of genetically encoded H2 O2 sensors, such as HyPer and roGFP2-Orp1. These H2 O2 sensors, combined with the detection of specific proteins modified by H2 O2 , will allow a deeper understanding of its signalling roles.

Modeling of Electron and Proton Transport in Chloroplast Membranes with Regard to Thioredoxin-Dependent Activation of the Calvin–Benson Cycle and ATP Synthase

In this work, the analysis of electron and proton transport in chloroplasts of higher plants has been carried out on the basis of a mathematical model, which takes into account the pH-dependent regulation of electron transfer and thioredoxin-dependent activation of the Calvin–Benson cycle (CBC) enzymes and the ATP synthase. The impact of reduced thioredoxin on the kinetics of electron transport, pH changes in the intrathylakoid space and ATP production has been simulated. Comparison of the computed and experimental data on the kinetics of P700 photooxidation has shown that the consideration of thioredoxin-dependent activation of the CBC and the ATP synthase provides an adequate description of the multiphase kinetics of P 700 + induction. The dynamics of electron flow through PSI and the partitioning of electron fluxes on the acceptor site of PSI has been simulated. The model predicts that at the initial stage of the induction period the alternative pathways, cyclic electron transport around PSI and electron flow to O2 (the Mehler reaction), play a significant role in photosynthetic electron transport chain, but their contribution attenuates upon the activation of the CBC reactions.

The cytochrome b6f complex: DFT modeling of the first step of plastoquinol oxidation by the iron-sulfur protein

In chloroplasts, the cytochrome (Cyt) b6f complex (plastoquinol-plastocyanin-oxidoreductase) provides connectivity between photosystems (PS) II and I, oxidizing plastoquinol (PQH2) formed in PSII and reducing plastocyanin (electron donor to PSI). The overall rate of the intersystem electron transport is determined by PQH2 oxidation by the Cyt b6f complex. In this work, using the DFT method, we have modeled the first step of PQH2 oxidation by the iron-sulfur protein (ISP) of the Cyt b6f complex. The model system contained the iron–sulfur cluster [Fe2S2], surrounding amino acid residues, and 2,3,5-trimethylbenzoquinol (TMBQH2), the tailless analog of PQH2. The energy profiles of the H atom transfer from TMBQH2 to the iron-sulfur protein (ISP) were calculated for two modes of the H-transfer, “diabatic” and “adiabatic”. The energies of transient states were estimated as 18.4 and 14.4 kcal mol−1. The energy effects of the reaction were evaluated as 7.7 and −0.2 kcal mol−1, respectively. The analysis of partial spin densities and electric charges on the atoms of the model system supports the bidirectional mechanism of the H-transfer reaction: an electron is directed to the Fe(1) atom of the [Fe2S2] cluster of the ISP, and a proton is accepted by the Nε atom of the His155 residue liganding the Fe(1) atom. Using the results of DFT computations of the energy profiles for the H-transfer reaction, we estimated the rate constants of quinol oxidation within the framework of the Marcus-Dutton-Crofts approach. Our analysis supports the diabatic model of the H-transfer, which implies that the elementary steps of electron and proton transfer occur much more rapidly than the concomitant changes in the system geometry. The rate constants estimated for this mode of H-transfer are in reasonable agreement with experimental data on the intersystem electron transport in chloroplasts.

Phosphoglycerate Kinases Are Co-Regulated to Adjust Metabolism and to Optimize Growth.

In plants, phosphoglycerate kinase (PGK) converts 1,3-bisphosphoglycerate into 3-phosphoglycerate in glycolysis but also participates in the reverse reaction in gluconeogenesis and the Calvin-Benson cycle. In the databases, we found three genes that encode putative PGKs. Arabidopsis (Arabidopsis thaliana) PGK1 was localized exclusively in the chloroplasts of photosynthetic tissues, while PGK2 was expressed in the chloroplast/plastid of photosynthetic and nonphotosynthetic cells. PGK3 was expressed ubiquitously in the cytosol of all studied cell types. Measurements of carbohydrate content and photosynthetic activities in PGK mutants and silenced lines corroborated that PGK1 was the photosynthetic isoform, while PGK2 and PGK3 were the plastidial and cytosolic glycolytic isoforms, respectively. The pgk1.1 knockdown mutant displayed reduced growth, lower photosynthetic capacity, and starch content. The pgk3.2 knockout mutant was characterized by reduced growth but higher starch levels than the wild type. The pgk1.1 pgk3.2 double mutant was bigger than pgk3.2 and displayed an intermediate phenotype between the two single mutants in all measured biochemical and physiological parameters. Expression studies in PGK mutants showed that PGK1 and PGK3 were down-regulated in pgk3.2 and pgk1.1, respectively. These results indicate that the down-regulation of photosynthetic activity could be a plant strategy when glycolysis is impaired to achieve metabolic adjustment and optimize growth. The double mutants of PGK3 and the triose-phosphate transporter (pgk3.2 tpt3) displayed a drastic growth phenotype, but they were viable. This implies that other enzymes or nonspecific chloroplast transporters could provide 3-phosphoglycerate to the cytosol. Our results highlight both the complexity and the plasticity of the plant primary metabolic network.

Electron and proton transfer in chloroplasts in silico. 2: The effect of diffusion limitations on the process of photosynthesis in spatially inhomogeneous thylakoids

The lateral mobility of protons and mobile electron carriers (plastoquinone and plastocyanin) is subjected to diffusion limitations; the effect of these limitations on the kinetics of photoinduced pH i changes has been investigated in the present work for metabolic states 3 (conditions of intensive ATP synthesis) and 4 (the state of photosynthetic control). Computer simulations were based on a mathematical model of electron and proton transport in chloroplasts developed earlier by the authors. Non-uniform distribution of electron carriers and ATP synthase complexes in the membranes of grana and intergranal thylakoids was taken into account in the model. The kinetics of intrathylakoid pH i changes and the lateral profiles of distribution of the mobile electron transporters in granal and intergranal thylakoids were studied. The formation of non-uniform pH i profiles (with lumen acidification in the central parts of the grana being substantially slower than in the stromal thylakoids) was shown to occur under the conditions of ATP synthesis. Variation of the diffusion coefficients of intrathylakoid hydrogen ions and mobile electron carriers (plastoquinone and plastocyanin) can have substantial effects on the lateral pH i profiles and the redox state of the mobile electron carriers.

Synthesis and Free Radical Scavenging Activity of New Hydroxybenzylidene Hydrazines.

Hydroxybenzylidene hydrazines exhibit a wide spectrum of biological activities. Here, we report synthesis and free radical scavenging activity of nine new N-(hydroxybenzylidene)-N′-[2,6-dinitro-4-(trifluoromethyl)]phenylhydrazines. The chemical structures of these compounds were confirmed by 1H-NMR, 13C-NMR, 19F-NMR, IR spectroscopy, LC-MS, and elemental analysis. The prepared compounds were tested for their activity to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH), galvinoxyl radical (GOR), and 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulphonic acid (ABTS) radicals. The free radical scavenging activity expressed as SC50 values of these compounds varied in a wide range, from a strong to no radical scavenging effect. The most effective radical scavengers were hydroxybenzylidene hydrazines containing three hydroxyl groups in the benzylidene part of their molecules. The prepared compounds were also tested for their activity to inhibit photosynthetic electron transport in spinach chloroplasts. IC50 values of these compounds varied in wide range, from an intermediate to no inhibitory effect.

Photosynthetic Electron and Proton Transport in Chloroplasts: EPR Study of ΔpH Generation, an Overview.

This is a brief overview focused on the electron paramagnetic resonance applications to the study of the proton transport processes in chloroplasts. After brief description of structural and functional organization of the chloroplast electron transport chain, our attention is focused on the measurements of trans-thylakoid pH difference (ΔpH) with pH-sensitive spin-probes. The use of spin-probes is based either (i) on measuring the ΔpH-partitioning of spin-probes between the thylakoid lumen and external volume, or (ii) on monitoring changes in the electron paramagnetic resonance spectra of pH-sensitive nitroxide radicals located in the lumen. Along with the use of spin-probes, the intra-thylakoid pH (pHin) can be determined by the "kinetic" method, which relies on the fact that the rate-limiting step in the chain of photosynthetic electron transfer (plastoquinol oxidation by the cytochrome b 6 f complex) is controlled by pHin. The results of ΔpH determinations in chloroplasts based on the use of pH-sensitive spin-probes and measurements of post-illumination reduction of photoreaction centers of Photosystem I are discussed in the context of the problem of energy coupling in laterally heterogeneous lamellar system of chloroplasts.

Antimycobacterial N-alkoxyphenylhydroxynaphthalenecarboxamides affecting photosystem II

N-(Alkoxyphenyl)-2-hydroxynaphthalene-1-carboxamides (series A) and N-(alkoxyphenyl)-1-hydroxynaphthalene-2-carboxamides (series B) affecting photosystem (PS) II inhibited photosynthetic electron transport (PET) in spinach chloroplasts. Their inhibitory activity depended on the compound lipophilicity as well as on the position of the alkoxy substituent. The most potent PET inhibitors were 2-hydroxy-N-phenylnaphthalene-1-carboxamide and N-[3-(but-2-yloxy)phenyl]-2-hydroxynaphthalene-1-carboxamide within series A (IC50=28.9 and 42.5µM, respectively) and 1-hydroxy-N-(3-propoxyphenyl)naphthalene-2-carboxamide and 1-hydroxy-N-(3-ethoxyphenyl)-naphthalene-2-carboxamide (IC50=2.0 and 3.1µM, respectively) within series B. The inhibitory activity of C′(3) or C′(4) alkoxy substituted compounds of series B was considerably higher than that of C′(2) ones within series A. The PET-inhibiting activities of both series were compared with the PET inhibition of isomeric N-alkoxyphenyl-3-hydroxynaphthalene-2-carboxamides (series C) reported recently. Interactions of the studied compounds with chlorophyll a and aromatic amino acids present in pigment–protein complexes mainly in PS II were documented by fluorescence spectroscopy. The section between P680 and plastoquinone QB in the PET chain occurring on the acceptor side of PSII can be suggested as the site of action of the compounds.