Exploring the hidden treasures of Nitella hyalina: a comprehensive study on its biological compounds, nutritional profile, and unveiling its antimicrobial, antioxidative, and hypoglycemic properties.

Macroalgae has the potential to be a precious resource in food, pharmaceutical, and nutraceutical industries. Therefore, the present study was carried out to identify and quantify the phyco-chemicals and to assess the nutritional profile, antimicrobial, antioxidant, and anti-diabetic properties of Nitella hyalina extracts. Nutritional composition revealed0.05 ± 2.40% ash content, followed by crude protein (24.66 ± 0.95%), crude fat (17.66 ± 1.42%), crude fiber (2.17 ± 0.91%), moisture content (15.46 ± 0.48%) and calculated energy value (173.50 ± 2.90 Kcal/100 g). 23 compounds were identified through GC-MS analysis in ethyl acetate extract, with primary compounds being Palmitic acid, methyl ester, (Z)-9-Hexadecenoic acid, methyl ester, and Methyl tetra decanoate. Whereas 15 compounds were identified in n-butanol extract, with the major compounds being Tetra decanoic acid, 9-hexadecanoic acid, Methyl pentopyranoside, and undecane. FT-IR spectroscopy confirmed the presence of alcoholic phenol, saturated aliphatic compounds, lipids, carboxylic acid, carbonyl, aromatic components, amine, alkyl halides, alkene, and halogen compounds. Moreover, n-butanol contains 1.663 ± 0.768 mg GAE/g, of total phenolic contents (TPC,) and 2.050 ± 0.143 QE/g of total flavonoid contents (TFC), followed by ethyl acetate extract, i.e. 1.043 ± 0.961 mg GAE/g and 1.730 ± 0.311 mg QE/g respectively. Anti-radical scavenging effect in a range of 34.55-46.35% and 35.39-41.79% was measured for n-butanol and ethyl acetate extracts, respectively. Antimicrobial results declared that n-butanol extract had the highest growth inhibitory effect, followed by ethyl acetate extract. Pseudomonas aeruginosa was reported to be the most susceptible strain, followed by Staphylococcus aureus and Escherichia coli, while Candida albicans showed the least inhibition at all concentrations. In-vivo hypoglycemic study revealed that both extracts exhibited dose-dependent activity. Significant hypoglycemic activity was observed at a dose of 300 mg/kg- 1 after 6 h i.e. 241.50 ± 2.88, followed by doses of 200 and 100 mg/kg- 1 (245.17 ± 3.43 and 250.67 ± 7.45, respectively) for n-butanol extract. In conclusion, the macroalgae demonstrated potency concerning antioxidant, antimicrobial, and hypoglycemic properties.

Cytogenotoxic, insecticidal, and phytotoxic activity from biomass extracts of the freshwater algae Nitella furcata.

Agroecology, the application of ecological concepts to agricultural production, has been developing over the last years with consequent promotion for discovery of bioactive compounds to control pests and abolish crop diseases. In this context, algae from Nitella genus are characterized by high potential for bioeconomic applications due to (1) available biomass for harvesting or cultivation and (2) production of allelochemicals, which present a potential to protect field crops from insect infestation. Therefore, this study aimed to determine primary and secondary metabolites derived from aqueous and hydroethanolic extracts of Nitella furcata and to evaluate phytotoxic, cytogenotoxic, insecticidal, and pro-oxidative activities of these extracts. Determination of metabolites showed the presence predominantly of carbohydrates, proteins, phenols, and flavonoids in hydroethanolic extract. Both extracts of N. furcata interfered in the germination of seeds and development of seedlings of Lactuca sativa, with hydroethanolic extract exhibiting greater inhibition. Both extracts also interfered with meristematic cells of Allium cepa as evidenced by chromosomal alterations and higher pro-oxidative activity. Aqueous extract at 5 and 0 mg/ml produced 100% insect mortality. Further, hydroethanolic extract at 0 mg/ml was lethal immediately upon exposure. Therefore, results demonstrate that N. furcata is potential algae species to be considered for development of environmental and ecotoxicological studies as a source of compounds with potential use in agroecological strategies.

The Reappearance of An Extremely Rare and Critically Endangered Nitella translucens (Charophyceae) in Poland.

We report the reappearance of the rare charophyte Nitella translucens in Poland. It was identified in the soft-water lobelian Lake Jelen (North Poland) during 2013 and 2018 phytolittoral surveys. This species is considered critically endangered in various European countries and was previously classified as extinct in Poland. Its occurrence was confirmed using morphological and molecular data (ITS1-18S, ITS2-28S, rDNA, and rbcL). The N. translucens occupied ~20% of the lake bottom, at depths of 1.5-6.5 m, water pH 7.5-8.6, conductivity of 59-66 µS · cm-1 , and total nitrogen and phosphorus during growing season in the range of 1.1-1.4 mg · L-1 and 0.07-0.1 mg · L-1 , respectively. It co-occurred mainly with plant species typical for lobelia lakes: Isoetes lacustris, Littorella uniflora, and Myriophyllum alterniflorum, as well as Ceratophyllum demersum and Elodea canadensis, which are characteristic for eutrophicated waters. It appears that N. translucens may thrive in lobelia lakes during their transformation to more eutrophic states.

The seasonal effects on the encrustation of charophytes in two hard-water lakes.

Encrustation and element content of six charophyte species from two hard-water lakes were investigated monthly for a period of 1 year. Seasonal patterns were analyzed for the interaction of water chemistry. Encrustation followed a seasonal pattern for Chara contraria, Chara subspinosa, and Nitellopsis obtusa in Lake Krüselin and for Chara globularis and Chara tomentosa in Lake Lützlow. However, no seasonality in the precipitated CaCO3 was observed for C. subspinosa in Lake Lützlow and for C. tomentosa in Lake Krüselin, indicating a lake-specific dependency. Species-specific encrustation was found. Chara contraria and N. obtusa encrusted the most in June and August, whereas C. subspinosa and Nitella flexilis/opaca exhibited lowest encrustation in March and April. The precipitated CaCO3 of charophytes correlated negatively to the concentration of total inorganic carbon in both lakes. Element content of plant dry weight was species-specific for Ca and K, and lake-specific for Mg. No specific pattern was found for the TP and Fe contents. The results showed seasonal, species, and lake-specific influences on the encrustation of charophytes.

The phytochelatin synthase from Nitella mucronata (Charophyta) plays a role in the homeostatic control of iron(II)/(III).

Although some charophytes (sister group to land plants) have been shown to synthesize phytochelatins (PCs) in response to cadmium (Cd), the functional characterization of their phytochelatin synthase (PCS) is still completely lacking. To investigate the metal response and the presence of PCS in charophytes, we focused on the species Nitella mucronata. A 40 kDa immunoreactive PCS band was revealed in mono-dimensional western blot by using a polyclonal antibody against Arabidopsis thaliana PCS1. In two-dimensional western blot, the putative PCS showed various spots with acidic isoelectric points, presumably originated by post-translational modifications. Given the PCS constitutive expression in N. mucronata, we tested its possible involvement in the homeostasis of metallic micronutrients, using physiological concentrations of iron (Fe) and zinc (Zn), and verified its role in the detoxification of a non-essential metal, such as Cd. Neither in vivo nor in vitro exposure to Zn resulted in PCS activation and PC significant biosynthesis, while Fe(II)/(III) and Cd were able to activate the PCS in vitro, as well as to induce PC accumulation in vivo. While Cd toxicity was evident from electron microscopy observations, the normal morphology of cells and organelles following Fe treatments was preserved. The overall results support a function of PCS and PCs in managing Fe homeostasis in the carophyte N. mucronata.

Growth and Oxidative Stress of Brittlewort (Nitella pseudoflabellata) in Response to Cesium Exposure.

The present study evaluated the impact of cesium ((133)Cs) at four concentrations (0, 0.001, 0.01, and 0.1 mg L(-1)) on growth, concentrations of chlorophyll and carotenoid pigments, and oxidative stress responses in the charophyte, Nitella pseudoflabellata, over 30 days. Oxidative stress was quantified by measuring anti-oxidant enzyme activities and H2O2 content. When compared with the control, significantly elevated activity levels of the anti-oxidative enzymes ascorbic peroxidase, catalase and guaiacol peroxidase were observed at 0.1 mg L(-1) (all p < 0.05), even though the H2O2 level was not significantly elevated. Carotenoid and chlorophyll a and b pigment levels were significantly reduced (all p < 0.05) at Cs exposures of 0.01 and 0.1 mg L(-1). Photosynthetic efficiency (i.e., Fv/Fm) was significantly reduced (p < 0.05) at Cs concentrations ≥0.001 mg L(-1). Significant reduction (p < 0.05) of plant growth (i.e., shoot length) was also observed after 1 week of exposure at Cs concentrations ≥0.001 mg L(-1). Our results suggested that Cs exposure reduced plant growth and affected plant functioning via activating the defense mechanism against oxidative stress in Nitella.

Diffusive Promotion by Velocity Gradient of Cytoplasmic Streaming (CPS) in Nitella Internodal Cells.

Cytoplasmic streaming (CPS) is well known to assist the movement of nutrients, organelles and genetic material by transporting all of the cytoplasmic contents of a cell. CPS is generated by motility organelles that are driven by motor proteins near a membrane surface, where the CPS has been found to have a flat velocity profile in the flow field according to the sliding theory. There is a consistent mixing of contents inside the cell by CPS if the velocity gradient profile is flattened, which is not assisted by advection diffusion but is only supported by Brownian diffusion. Although the precise flow structure of the cytoplasm has an important role for cellular metabolism, the hydrodynamic mechanism of its convection has not been clarified. We conducted an experiment to visualise the flow of cytoplasm in Nitella cells by injecting tracer fluorescent nanoparticles and using a flow visualisation system in order to understand how the flow profile affects their metabolic system. We determined that the velocity field in the cytosol has an obvious velocity gradient, not a flattened gradient, which suggests that the gradient assists cytosolic mixing by Taylor-Aris dispersion more than by Brownian diffusion.

A survey of PPR proteins identifies DYW domains like those of land plant RNA editing factors in diverse eukaryotes.

The pentatricopeptide repeat modules of PPR proteins are key to their sequence-specific binding to RNAs. Gene families encoding PPR proteins are greatly expanded in land plants where hundreds of them participate in RNA maturation, mainly in mitochondria and chloroplasts. Many plant PPR proteins contain additional carboxyterminal domains and have been identified as essential factors for specific events of C-to-U RNA editing, which is abundant in the two endosymbiotic plant organelles. Among those carboxyterminal domain additions to plant PPR proteins, the so-called DYW domain is particularly interesting given its similarity to cytidine deaminases. The frequency of organelle C-to-U RNA editing and the diversity of DYW-type PPR proteins correlate well in plants and both were recently identified outside of land plants, in the protist Naegleria gruberi. Here we present a systematic survey of PPR protein genes and report on the identification of additional DYW-type PPR proteins in the protists Acanthamoeba castellanii, Malawimonas jakobiformis, and Physarum polycephalum. Moreover, DYW domains were also found in basal branches of multi-cellular lineages outside of land plants, including the alga Nitella flexilis and the rotifers Adineta ricciae and Philodina roseola. Intriguingly, the well-characterized and curious patterns of mitochondrial RNA editing in the slime mold Physarum also include examples of C-to-U changes. Finally, we identify candidate sites for mitochondrial RNA editing in Malawimonas, further supporting a link between DYW-type PPR proteins and C-to-U editing, which may have remained hitherto unnoticed in additional eukaryote lineages.

The characean internodal cell as a model system for studying wound healing.

This work describes the characean internodal cell as a model system for the study of wound healing and compares wounds induced by certain chemicals and UV irradiation with wounds occurring in the natural environment. We review the existing literature and define three types of wound response: (1) cortical window formation characterised by disassembly of microtubules, transient inhibition of actin-dependent cytoplasmic streaming and chloroplast detachment, (2) fibrillar wound walls characterised by exocytosis of vesicles carrying wall polysaccharides and membrane-bound cellulose synthase complexes coupled with endocytosis of surplus membrane and (3) amorphous, callose- and membrane-containing wound walls characterised by exocytosis of vesicles and endoplasmic reticulum cisternae in the absence of membrane recycling. We hypothesize that these three wound responses reflect the extent of damage, probably Ca(2+) influx, and that the secretion of Ca(2+) -loaded endoplasmic reticulum cisternae is an emergency reaction in case of severe Ca(2+) load. Microtubules are not required for wound healing but their disassembly could have a signalling function. Transient reorganisation of the actin cytoskeleton into a meshwork of randomly oriented filaments is required for the migration of wound wall forming organelles, just as occurs in tip-growing plant cells. New data presented in this study show that during the deposition of an amorphous wound wall numerous actin rings are present, which may indicate specific ion fluxes and/or a storage form for actin. In addition, we present new evidence for the exocytosis of FM1-43-stained organelles, putative endosomes, required for plasma membrane repair during wound healing. Finally, we show that quickly growing fibrillar wound walls, even when deposited in the absence of microtubules, have a highly ordered helical structure of consistent handedness comprised of cellulose microfibrils.

Actin-dependent deposition of putative endosomes and endoplasmic reticulum during early stages of wound healing in characean internodal cells.

We investigated the behaviour of organelles stained with FM1-43 (putative endosomes) and/or LysoTracker Red (LTred; acidic compartments) and of the endoplasmic reticulum (ER) during healing of puncture and UV-induced wounds in internodal cells of Nitella flexilis and Chara corallina. Immediately after puncture, wounds were passively sealed with a plug of solid vacuolar inclusions, onto which a bipartite wound wall was actively deposited. The outer, callose-containing amorphous layer consisted of remnants of FM1-43- and LTred-labelled organelles, ER cisternae and polysaccharide-containing secretory vesicles, which became deposited in the absence of membrane retrieval (compound exocytosis). During formation of the inner cellulosic layer, exocytosis of secretory vesicles with the newly formed plasma membrane is coupled to endocytosis via coated vesicles. Migration of FM1-43- and LTred-stained organelles, ER and secretory vesicles towards the cell cortex and deposition of a bipartite wound wall could also be induced by spot-like irradiation with ultraviolet light. Cytochalasin D reversibly inhibited the accumulation and deposition of organelles. Our study indicates that active actin-dependent deposition of putative recycling endosomes is required for wound healing (plasma membrane repair) and supports the hypothesis that deposition of ER cisternae helps to restore wounding-disturbed Ca(2+) metabolism.

Phycoremediation of Chromium (VI) by Nitella and impact of calcium encrustation.

This article discusses the applicability of the Charophyte, Nitella pseudoflabellata in the remediation of Cr (VI) contaminated waters at different calcifying potentials. Its growth was found to be positively correlated with Ca in water (CaW), but marginally significant in the presence of Cr (VI) in water (CrW). High CaW resulted in calcite encrustation on the plant cell wall. CaW was found to be aiding Cr (VI) fixation in the long run, as this correlated positively with both CaW and CrW. However, Ca interfered with passive Cr (VI) accumulation in live plant matter at low CrW concentrations (1mg/g Cr dry weight of plant. Cr (VI) concentrations greater than 0.4 mg/L were too toxic, showing maximum quantum efficiency of PSII photochemistry (F(v)/F(m)) values<0.63. The opposite was noticed (F(v)/F(m)>0.76) when Cr (VI) was less than 0.2mg/L. Elongation curve patterns based on shoot lengths showed similar scenarios. In all cases high CaW units with calcite encrustation found to be least affected by Cr (VI) toxicity. Optimum remediation was obtained using a combination of high Ca and Cr (VI) in the case of passive (short-term) operation and low Ca and Cr (VI) for active (long-term) operation. Under the passive scenario, plants accumulated above 1.2mg/g Cr dry weight whereas in the active case, accumulation was 0.8 mg/g Cr dry weight. We conclude that Nitella-mediated Cr (VI) remediation is a promising technique within the range and conditions investigated.

Microtubule-dependent motility and orientation of the cortical endoplasmic reticulum in elongating characean internodal cells.

Motility of the endoplasmic reticulum (ER) is predominantly microtubule- dependent in animal cells but thought to be entirely actomyosin-dependent in plant cells. Using live cell imaging and transmission electron microscopy to examine ER motility and structural organization in giant internodal cells of characean algae, we discovered that at the onset of cell elongation, the cortical ER situated near the plasma membrane formed a tight meshwork of predominantly transverse ER tubules that frequently coaligned with microtubules. Microtubule depolymerization increased mesh size and decreased the dynamics of the cortical ER. In contrast, perturbing the cortical actin array with cytochalasins did not affect the transverse orientation but decreased mesh size and increased ER dynamics. Our data suggest that myosin-dependent ER motility is confined to the ER strands in the streaming endoplasm, while the more sedate cortical ER uses microtubule-based mechanisms for organization and motility during early stages of cell elongation. We show further that the ER has an inherent, NEM-sensitive dynamics which can be altered via interaction with the cytoskeleton and that tubule formation and fusion events are cytoskeleton-independent.

[Interaction of melittin with ion channels of excitable membranes].

The effect of the neurotoxin melittin on the activation of ion channels of excitable membrane, the plasmalemma of Characeae algae cells, isolated membrane patches of neurons of mollusc L. stagnalis and Vero cells was studied by the method of intracellular perfusion and the patch-clamp technique in inside-out configuration. It was shown that melittin disturbs the conductivity of plasmalemma and modifieds Ca(2+)-channels of plant membrane. The leakage current that appears by the action of melittin can be restored by substituting calmodulin for melittin. Melittin modifies K(+)-channels of animal cell membrane by disrupting the phospholipid matrix and forms conductive structures in the membrane by interacting with channel proteins, which is evidenced by the appearance of additional ion channels.

Wide-ranging effects of eight cytochalasins and latrunculin A and B on intracellular motility and actin filament reorganization in characean internodal cells.

Numerous forms of cytochalasins have been identified and, although they share common biological activity, they may differ considerably in potency. We investigated the effects of cytochalasins A, B, C, D, E, H and J and dihydrocytochalasin B in an ideal experimental system for cell motility, the giant internodal cells of the characean alga Nitella pseudoflabellata. Cytochalasins D (60 microM) and H (30 microM) were found to be most suited for fast and reversible inhibition of actin-based motility, while cytochalasins A and E arrested streaming at lower concentrations but irreversibly. We observed no clear correlation between the ability of cytochalasins to inhibit motility and the actual disruption of the subcortical actin bundle tracks on which myosin-dependent motility occurs. Indeed, the actin bundles remained intact at the time of streaming cessation and disassembled only after one to several days' treatment. Even when applied at concentrations lower than that required to inhibit cytoplasmic streaming, all of the cytochalasins induced reorganization of the more labile cortical actin filaments into actin patches, swirling clusters or short rods. Latrunculins A and B arrested streaming only after disrupting the subcortical actin bundles, a process requiring relatively high concentrations (200 microM) and very long treatment periods of >1 d. Latrunculins, however, worked synergistically with cytochalasins. A 1 h treatment with 15 nM latrunculin A and 4 microM cytochalasin D induced reversible fragmentation of subcortical actin bundles and arrested cytoplasmic streaming. Our findings provide insights into the mechanisms by which cytochalasins and latrunculins interfere with characean actin to inhibit motility.

[Long-term production dynamics of aquatic vegetation in the Arakhlei Lake (Eastern Transbaikalia)].

Long-term data on aquatic vegetation production in the mesotrophic Arakhlei Lake was comparatively analyzed. The results demonstrated that the production dynamics of aquatic vegetation communities depend on the water-level conditions of the lake. The data on the succession of dominant vegetation communities are given: Chara sp. and Ceratophyllum demersum --> C. demersum and Lemna trisulca. At the same time, the increased proportion of C. demersum and L. trisulca pointed to an increased anthropogenic stress on the lake.

Removal of the nitro and phenyl groups from NPPB decreases its inhibitory effect on cytoplasmic streaming in the alga Nitella hookeri.

Structural analogues of the arylaminobenzoate 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), prepared using a simple reductive amination sequence, were tested for their effects on cytoplasmic streaming rates in the alga Nitella hookeri. Cytoplasmic streaming was sensitive to NPPB, with an IC50 value of 24 micromol/L. Removal of the nitro group from the benzoate ring decreased the IC50 to 455 micromol/L. The introduction of an extra carbon or double bond into the aliphatic chain had no effect on activity. Loss of the phenyl group decreased potency, with an IC50 of 6.4 mmol/L. These data are the first documenting the relative inhibitory effects of structural changes to arylaminobenzoates in algae. Patch-clamp data and the effects of tetrapentyl ammonium chloride on streaming suggest that the nitro and phenyl groups may act by inhibiting both K+ and Cl- channels. This is likely, through changes in the membrane potential, to affect Ca2+ fluxes and action potentials, thereby slowing cytoplasmic streaming.

[Estimation of efficiency of complex-method intestinal therapy using Nitella flexilis test-object for acute intestinal obstruction of various etiology].

The aim of our investigation was to define the presence of correlation between toxicity of intestinal contents and clinical and laboratory indices in the cases of ileus and peritonitis with the use of complex method of enteral therapy. Experiments have been carried out on internodal cells of Nitella Flexilis water plant. Efficiency of the given method (investigation of toxicity of the intestinal content with the use of test-object Nitella Flexilis) has been studied in 25 patients, who underwent correction of morpho-functional status of small intestine. Results of investigation have shown that changes in toxicity of intestinal content reliably reflect the nature and dynamics of the pathobiologic processes proceeding in GIS in treated patients suffering from acute intestinal impassability. Using the method of correction of morpho-functional status of small intestine decreases the role of "Intestinal factor" in formation of endogenous intoxication, which in turn results in early normalization of clinical and laboratory indices, favored process of early post-operational period, decreased rate of lethality and shortened rehabilitation period.

Toxicological studies of pesticides on cytoplasmic streaming in Nitella.

In the present study, changes in velocity of cytoplasmic streaming in the giant internodal cells of Nitella for varying concentration of the pesticides, 2,4-D, dieldrin, malathion, methyl parathion and endosulfan, were measured. Marked decrease in the velocity of cytoplasmic streaming was found at the concentrations of 0.01, 0.1, 1, 10 and 100mM. Dieldrin was the most toxic to all the pesticides investigated, followed by methyl parathion, endosulfan, malathion and 2,4-D. Threshold values for dieldrin, methylparathion, endosulfan, malathion and 2,4-D as indicated by the onset of decrease in the normal cytoplasmic streaming velocity were less than 6.25 x 10(-6), 2.5 x 10(-5), 5 x 10(-5), 5 x 10(-5) and 1.25 x 10(-5)M respectively. Cessation of streaming was noticed above 1mM in dieldrin and above 10mM when exposed to methylparathion and endosulfan. Cessation of streaming was not seen up to 100mM concentration of 2,4-D and malathion.

Actin-dependent motility of melanosomes from fish retinal pigment epithelial (RPE) cells investigated using in vitro motility assays.

Melanosomes (pigment granules) within retinal pigment epithelial (RPE) cells of fish and amphibians undergo massive migrations in response to light conditions to control light flux to the retina. Previous research has shown that melanosome motility within apical projections of dissociated fish RPE cells requires an intact actin cytoskeleton, but the mechanisms and motors involved in melanosome transport in RPE have not been identified. Two in vitro motility assays, the Nitella assay and the sliding filament assay, were used to characterize actin-dependent motor activity of RPE melanosomes. Melanosomes applied to dissected filets of the Characean alga, Nitella, moved along actin cables at a mean rate of 2 microm/min, similar to the rate of melanosome motility in dissociated, cultured RPE cells. Path lengths of motile melanosomes ranged from 9 to 37 microm. Melanosome motility in the sliding filament assay was much more variable, ranging from 0.4-33 microm/min; 70% of velocities ranged from 1-15 microm/min. Latex beads coated with skeletal muscle myosin II and added to Nitella filets moved in the same direction as RPE melanosomes, indicating that the motility is barbed-end directed. Immunoblotting using antibodies against myosin VIIa and rab27a revealed that both proteins are enriched on melanosome membranes, suggesting that they could play a role in melanosome transport within apical projections of fish RPE.

Membrane potential genesis in Nitella cells, mitochondria, and thylakoids.

The resting membrane potential of Nitella cells shifts in parallel with the change in H+ equilibrium potential, but is not equal to the H+ equilibrium potential. The deviation of the membrane potential from the H+ equilibrium potential depends on the extrusion rate of H+ by the electrogenic H+-pump. The activity of the electrogenic H+-pump was formulated in terms of the change in the free energy of ATP hydrolysis. The deviation of membrane potential from the H+ equilibrium potential induces a passive H+ flow. The passive inward H+ current may be coupled with Cl- uptake. The coupling rate of H+,Cl- co-transport was discussed. The membrane potential of mitochondria was electrochemically formulated in terms of oxidation-reduction H2/H+ half-cells spontaneously formed at the inner and outer boundaries of each trans-membrane electron-conducting pathway. The membrane potential formed by a pair of H2/H+ redox cells is pH-sensitive in its nature, but deviates from the H+ equilibrium potential to an extent that depends on the logarithm of the ratio of H2 concentrations at the inner and outer boundaries. The membrane potential of thylakoids is considered to be primarily due to the electromotive force of photocells embedded in the thylakoid membrane, as far as the anode and cathode of each photocell are in contact with the inner and outer solutions, respectively. The light-induced electronic current yields oxygen at the inner boundary and causes an increase in the H2 pool at the outer boundary of the electron-conducting pathway, which has no shunting plastoquinone chain between these two boundaries.