Photosynthetic Oxygen Evolution Research Articles

Toxicity of the sunscreen UV filter benzophenone-3 (OBZ) to the microalga Selenastrum capricornutum: An insight into OBZ’s damage to photosynthesis and respiration

Oxybenzone (OBZ; benzophenone-3, CAS# 131–57–7), as a new pollutant and ultraviolet absorbent, shows a significant threat to the survival of phytoplankton. This study aims to explore the acute toxic effects of OBZ on the growth of the microalga Selenastrum capricornutum, as well as the mechanisms for its damage to the primary metabolic pathways of photosynthesis and respiration. The results demonstrated that the concentrations for 50 % of maximal effect (EC50) of OBZ for S. capricornutum were 9.07 mg L−1 and 8.54 mg L−1 at 72 h and 96 h, respectively. A dosage of 4.56 mg L−1 OBZ significantly lowered the photosynthetic oxygen evolution rate of S. capricornutum in both light and dark conditions for a duration of 2 h, while it had no effect on the respiratory oxygen consumption rate under darkness. OBZ caused a significant decline in the efficiency of photosynthetic electron transport due to its damage to photosystem II (PSII), thereby decreasing the photosynthetic oxygen evolution rate. Over-accumulated H2O2 was produced under light due to the damage caused by OBZ to the donor and acceptor sides of PSII, resulting in increased peroxidation of cytomembranes and inhibition of algal respiration. OBZ’s damage to photosynthesis and respiration will hinder the conversion and reuse of energy in algal cells, which is an important reason that OBZ has toxic effects on S. capricornutum. The present study indicated that OBZ has an acute toxic effect on the microalga S. capricornutum. In the two most important primary metabolic pathways in algae, photosynthesis is more sensitive to the toxicity of OBZ than respiration, especially in the dark.

Rapid oxygen isotopic exchange between bicarbonate and water during photosynthesis

Whether rapid oxygen isotopic exchange between bicarbonate and water occurs in photosynthesis is the key to determine the source of oxygen by classic 18O-labeled photosynthetic oxygen evolution experiments. Here we show that both Microcystis aeruginosa and Chlamydomonas reinhardtii utilize a significant proportion (>16%) of added bicarbonate as a carbon source for photosynthesis. However, oxygen isotopic signal in added bicarbonate cannot be traced in the oxygen in organic matter synthesized by these photosynthetic organisms. This contradicts the current photosynthesis theory, which states that photosynthetic oxygen evolution comes only from water, and oxygen in photosynthetic organic matter comes only from carbon dioxide. We conclude that the photosynthetic organisms undergo rapid exchange of oxygen isotope between bicarbonate and water during photosynthesis. At the same time, this study also provides isotopic evidence for a new mechanism that half of the oxygen in photosynthetic oxygen evolution comes from bicarbonate photolysis and half comes from water photolysis, which provides a new explanation for the bicarbonate effect, and suggests that the Kok-Joliot cycle of photosynthetic oxygen evolution, must be modified to include a molecule of bicarbonate in addition to one molecule of water which in turn must be incorporated into the cycle instead of two water molecules. Furthermore, this study provides a theoretical basis for constructing a newer artificial photosynthetic reactor coupling light reactions with the dark reactions.

The photosynthetic oxygen evolution does not exclude the important role and contribution of bicarbonate photolysis

The photosynthetic oxygen evolution does not exclude the important role and contribution of bicarbonate photolysis

Illuminated septic tank – A microalgae assisted onsite wastewater treatment system

To reduce the anthropogenic nutrient loading into natural waterways, onsite wastewater treatment is essential for households without access to municipal sewer systems. However, many conventional septic tanks significantly underperform the centralized wastewater treatment. In the present study, a novel illuminated septic tank inoculated with the consortium of microalga Chlorella vulgaris and aerobic bacteria was developed by modifying the conventional configuration. The inclusion of microalgae facilitated aeration inside the septic tank through photosynthetic oxygen evolution, and the microalgae-bacteria consortium enhanced the wastewater treatment performance. With the operation at 15 ℃ and a hydraulic retention time of 2.5 days, the lab-scale algae-assisted septic tank significantly decreased the concentrations of ammonium-nitrogen (NH4+-N), soluble phosphorus (P), total P, and total chemical oxygen demand by 54%, 65.2%, 78.5%, and 90.7% in the discharged effluent, respectively (p < 0.05), whereas the conventional septic tank without microalgae did not exhibit any treatment of NH4+-N or soluble P and the total P removal efficiency was lower by 50%. Meanwhile, the photosynthetic activity of microalgae altered the gas composition in the tank headspace by consuming carbon dioxide, emitting oxygen, and inhibiting the evolution of methane, which further benefited the aeration requirement and contributed to the mitigation of greenhouse gas emissions from septic systems.

Photosynthetic response mechanism to polybrominated diphenyl ether exposure in Chlorella pyrenoidosa

Polybrominated diphenyl ether (PBDE) contamination is common in aquatic environments and can severely damage aquatic organisms. However, there is a lack of information on the response and self-adaptation mechanisms of these organisms. Chlorella pyrenoidosa was treated with 2,2′,4,4′-tetrabromodiphenyl ether (BDE47), causing significant growth inhibition, pigment reduction, oxidative stress, and chloroplast atrophy. Photosynthetic damage contributed to inhibition, as indicated by Fv/Fm, Chl a fluorescence induction, photosynthetic oxygen evolution activity, and photosystem subunit stoichiometry. Here, Chl a fluorescence induction and quinone electron acceptor (QA−) reoxidation kinetics showed that the PSII donor and acceptor sides were insensitive to BDE47. Quantitative analyses of D1 and PsaD proteins illustrated that PSII and PSI complexes were the main primary targets of photosynthesis inhibition by BDE47. Significant modulation of PSII complex might have been caused by the potential binding of BDE47 on D1 protein, and molecular docking was performed to investigate this. Increased activation of antioxidant defense systems and photosystem repair as a function of exposure time indicated a positive resistance to BDE47. After a 5-day exposure, 23 % of BDE47 was metabolized. Our findings suggest that C. pyrenoidosa has potential as a bioremediator for wastewater-borne PBDEs and can improve our understanding of ecological risks to microalgae.

Effects of selective RNA processing and stabilization enzymes on carbon sequestration by photosynthesis of Synechococcus sp. PCC7002

Synechococcus is one of the most abundant prokaryotic photosynthetic organisms on Earth and plays a key role in oceanic carbon fixation and transformation. To improve the photosynthetic efficiency of synechococcus, a post-transcriptional regulatory mechanism - Selective RNA Processing and Stabilization (SRPS) was considered. We inactivated the SRPS-enzymes, executor of the SRPS mechanism, to explore their regulation rule of photosynthetic carbon fixation efficiency in Synechococcus. The results showed that the inactivation of SRPS-enzymes mainly affected the growth rate or growth phase. It significantly alters the photosynthetic oxygen evolution rate, pigment content, chlorophyll fluorescence, carbon and nitrogen content, as well as the composition and biological activity of the dissolved organic matter derived from Synechococcus (SOM). Inactivating SRPS-enzymes results in an increase in the expression level of most subunits of the Cytochrome b6-f complex, while the expression levels of most subunits of PSI, PSII, RuBisCO, and NDH decrease. All SRPS-enzymes are involved in the expression regulation of basilic protein complexes in photosynthesis, such as PSI, PSII, Cytochrome b6-f complex, ATP synthase, and RuBisCO. Our results indicate that the inactivation of SRPS-enzymes have a significant influence on carbon sequestration by photosynthesis of Synechococcus sp. PCC7002.

Probing the Influence of Novel Organometallic Copper(II) Complexes on Spinach PSII Photochemistry Using OJIP Fluorescence Transient Measurements.

Modern agricultural cultivation relies heavily on genetically modified plants that survive after exposure to herbicides that kill weeds. Despite this biotechnology, there is a growing need for new sustainable, environmentally friendly, and biodegradable herbicides. We developed a novel [CuL2]Br2 complex (L = bis{4H-1,3,5-triazino[2,1-b]benzothiazole-2-amine,4-(2-imidazole) that is active on PSII by inhibiting photosynthetic oxygen evolution on the micromolar level. [CuL2]Br2 reduces the FV of PSII fluorescence. Artificial electron donors do not rescind the effect of [CuL2]Br2. The inhibitory mechanism of [CuL2]Br2 remains unclear. To explore this mechanism, we investigated the effect of [CuL2]Br2 in the presence/absence of the well-studied inhibitor DCMU on PSII-containing membranes by OJIP Chl fluorescence transient measurements. [CuL2]Br2 has two effects on Chl fluorescence transients: (1) a substantial decrease of the Chl fluorescence intensity throughout the entire kinetics, and (2) an auxiliary "diuron-like" effect. The initial decrease dominates and is observed both with and without DCMU. In contrast, the "diuron-like" effect is small and is observed only without DCMU. We propose that [CuL2]Br2 has two binding sites for PSII with different affinities. At the high-affinity site, [CuL2]Br2 produces effects similar to PSII reaction center inhibition, while at the low-affinity site, [CuL2]Br2 produces effects identical to those of DCMU. These results are compared with other PSII-specific classes of herbicides.

The electron–proton bottleneck of photosynthetic oxygen evolution

Photosynthesis fuels life on Earth by storing solar energy in chemical form. Today’s oxygen-rich atmosphere has resulted from the splitting of water at the protein-bound manganese cluster of photosystem II during photosynthesis. Formation of molecular oxygen starts from a state with four accumulated electron holes, the S4 state—which was postulated half a century ago1 and remains largely uncharacterized. Here we resolve this key stage of photosynthetic O2 formation and its crucial mechanistic role. We tracked 230,000 excitation cycles of dark-adapted photosystems with microsecond infrared spectroscopy. Combining these results with computational chemistry reveals that a crucial proton vacancy is initally created through gated sidechain deprotonation. Subsequently, a reactive oxygen radical is formed in a single-electron, multi-proton transfer event. This is the slowest step in photosynthetic O2 formation, with a moderate energetic barrier and marked entropic slowdown. We identify the S4 state as the oxygen-radical state; its formation is followed by fast O–O bonding and O2 release. In conjunction with previous breakthroughs in experimental and computational investigations, a compelling atomistic picture of photosynthetic O2 formation emerges. Our results provide insights into a biological process that is likely to have occurred unchanged for the past three billion years, which we expect to support the knowledge-based design of artificial water-splitting systems.

Enhancing overall carbon fixation and energy conversion with formate in green microalga Chlamydomonas reinhardtii

The natural carbon-concentration mechanism (CCM) is the solution to achieve high photosynthetic efficiency. Mimicking the natural CCM, exogenous formate which can be produced by renewable energy and CO2 artificially, was introduced into a model photosynthetic organism, Chlamydomonas reinhardtii, to improve the overall photosynthesis. To release the adverse effects of formate, the combination of different strategies, including co-substrate, evolution, and conditions optimization, the formate tolerance to over 40 mM, which was higher than previous irreversible inhibition limitation of formate on C. reinhardtii, was achieved, and formate-mediated enhancement of growth and photosynthesis activity was obtained with a 27 % biomass improvement and a 60 % increase in photosynthetic oxygen evolution. Interestingly, 82 % of formate was converted with the illumination, indicating the existence of energy interaction between photosynthesis and formate assimilation. Meanwhile, formate suppressed respiration and reduced a 29 % biomass decline in the night. Moreover, supported by the enzyme inhibitor, formate consumption, and biochemical compositions, it was postulated that formate was assimilated via the pyruvate formate-lyase (PFL) enzyme to stimulate the increase of photosynthetic components to maintain photosynthesis activity. With the overexpressed PFL and conditions optimization, formate could be further used as the sole organic carbon source for higher biomass in C. reinhardtii. This work presents the potentiality of introducing formate as artificial carbon intermediates to natural metabolic pathways for higher-than-nature photosynthetic efficiency.

Inactivation of photosynthetic cyclic electron transports upregulates photorespiration for compensation of efficient photosynthesis in Arabidopsis.

Plants have multiple mechanisms to maintain efficient photosynthesis. Photosynthetic cyclic electron transports around photosystem I (CET), which includes the PGR5/PGRL1 and NDH pathways, and photorespiration play a crucial role in photosynthetic efficiency. However, how these two mechanisms are functionally linked is not clear. In this study, we revealed that photorespiration could compensate for the function of CET in efficient photosynthesis by comparison of the growth phenotypes, photosynthetic properties monitored with chlorophyll fluorescence parameters and photosynthetic oxygen evolution in leaves and photorespiratory activity monitored with the difference of photosynthetic oxygen evolution rate under high and low concentration of oxygen conditions between the deleted mutant PGR5 or PGRL1 under NDH defective background (pgr5 crr2 or pgrl1a1b crr2). Both CET mutants pgr5 crr2 and pgrl1a1b crr2 displayed similar suppression effects on photosynthetic capacities of light reaction and growth phenotypes under low light conditions. However, the total CET activity and photosynthetic oxygen evolution of pgr5 crr2 were evidently lower than those of pgrl1a1b crr2, accompanied by the upregulation of photorespiratory activity under low light conditions, resulting in severe suppression of photosynthetic capacities of light reaction and finally photodamaged phenotype under high light or fluctuating light conditions. Based on these findings, we suggest that photorespiration compensates for the loss of CET functions in the regulation of photosynthesis and that coordination of both mechanisms is essential for maintaining the efficient operation of photosynthesis, especially under stressed conditions.

Photorespiration plays an important role in H2 production by marine Chlorella pyrenoidosa

Marine Chlorella pyrenoidosa was previously reported to produce H2 under nitrogen-deprived condition. In this study, the role of photorespiration in H2 production by C. pyrenoidosa was investigated. It was found that the expression level of genes encoding three enzymes involved in photorespiration decreased, but the expression level of gene encoding glutamate synthase increased in nitrogen-deprived culture compared with control, indicating a complex adjustment of photorespiration activity during H2 production by C. pyrenoidosa. The use of a photorespiration inhibitor led not only to a decrease in H2 production by 15 % under nitrogen deprivation condition, but also to a 16 % decrease in O2 evolution in the complete medium. Moreover, it was demonstrated that the total photosynthetic oxygen evolution and Fv/Fm declined when photorespiration was blocked. This suggested that, the photorespiration pathway does not directly participate in the production of photosynthetic electrons and the transfer of hydrogen producing electrons. However, it played an important role in photoprotection of PSII during H2 production by C. pyrenoidosa, which enabled PSII to provide more photosynthetic electrons to hydrogenase.

Novel ZIF-8@CHs catalysts for photocatalytic degradation of tetracycline hydrochloride

A novel ZIF-8@CHs photocatalyst, which was generated using the metal organic framework ZIF-8 and intact chloroplasts (CHs) from Chlorella sp. in a one-pot synthesis, was used in this study for the first time to degrade tetracycline hydrochloride (TCH) through photocatalysis. The results of systematic characterization demonstrated that ZIF-8@CHs was successfully p0repared. Meanwhile, ZIF-8@CHs exhibited excellent photocatalytic performance and good adaptability. Under the condition of simulated sunlight, the high porosity ZIF-8 shell enabled CHs to maintain typical photosynthetic oxygen evolution behavior in vitro, and using CHs as the core produced significant ROS, significantly improving the efficiency of TCH photocatalytic degradation. In addition, the radical trapping test and EPR spectra proved that O2–, 1O2, and •OH were the key active species for TCH degradation. Eventually, the ZIF-8@CHs system can not only expand the new concept of organic pollutant degradation in water bodies, but also offer recommendations for live organ envelope modification..

Effects of calcification on air-water CO2 fluxes in tropical seagrass meadows: A mesocosm experiment

Seagrass meadows deliver a range of ecosystem services, where one of the more important is the capacity to store carbon and serve as sinks for atmospheric carbon dioxide. The capacity of seagrass meadows for carbon storage might, however, be modified and complicated by several factors; one important factor is the possible effects of calcification within the meadows. In tropical areas, seagrass meadows can contain high proportions of calcareous organisms, which through their calcification may cause release of CO2. To study this aspect of the CO2 balance within tropical seagrass systems, we investigated the air-water CO2 flux in seagrass mesocosms with different plant community compositions, i.e. mixtures of seagrass and calcifying macroalgae, having similar overall photosynthetic oxygen evolution rates. The measured CO2 fluxes changed both in rate and direction over the day and were significantly related to plant community composition. Downward fluxes of CO2 were found only over vegetation with high proportion of seagrass and in the afternoon, whereas occurrence of calcifying algae appeared to reverse the flow. A partial least squares (PLS) regression model indicated that pH, pCO2 and dissolved inorganic carbon (DIC) were the primary environmental variables predicting the CO2 fluxes. Our findings show that algal calcification might partly counteract the carbon sequestration in seagrass meadows.

Productivity and nutrient removal by the microalga Chlamydopodium fusiforme grown outdoors in BG-11 and piggery wastewater

The objective of this work was to test the growth of the freshwater microalgaChlamydopodium fusiformeMACC-430 in diluted piggery wastewater (PWW) for biomass production which is a potential producer of biostimulating and antimicrobial compounds. The productivity and effectiveness in removing nitrogen and phosphorus by the cultures were tested outdoors in open ponds by comparing the mineral medium BG-11 medium (control) and piggery wastewater (PWW). Daily biomass yields were found 14.7 ± 4.6g m-2d-1in BG-11 and 17.6 ± 6.7g m-2d-1in 10-fold diluted wastewater (PWW10) with deionized water. Further increase in the biomass productivity yield (33.1 ± 5.6g m-2d-1) was achieved with more concentrated PWW (5-fold dilution – PWW5). Nitrogen removal rate (N-NH4+) reached 21.4 ± 2.9mg L-1d-1in cultures grown in PWW10 and increased to 38.4±16.3mg L-1d-1using the PWW5. The use of undiluted PWW strongly increased the bacterial load, which caused the loss of the culture. The photosynthetic performance measured as the maximum fluorescence yield Fv/Fmratio in both the PWW10 and BG-11 cultures showed a cyclic behavior, as it decreased during the day and recovered at night. However, in the cultures grown in diluted PWW the Fv/Fmratio slightly increased throughout the cultivation. Between PWW10 and BG-11, no significant differences were observed in photosynthetic oxygen evolution; on the contrary, PWW5 showed a 30% reduction compared to PWW10 and BG-11. Significantly lower chlorophyll and carotenoid contents were found in the cultures grown in PWW compared to BG-11. Biochemical composition showed a slightly higher protein content in biomass grown in PWW10 (53.4%) compared to BG-11 (52.7%). The protein content further increased (61.3%) when the more concentrated PWW5 was used. The biomass, particularly that produced on PWW, revealed antimicrobial activity against plant pathogens, including fungi, and oomycete, while rather weak biostimulant activity was determined for theC. fusiformebiomass independently of the cultivation medium. Results demonstrated thatC. fusiformeis a robust strain suitable to be grown in diluted PWW outdoors with a high nutrient removal rate.

Tuning photosynthetic oxygen for hydrogen evolution in synergistically integrated, sulfur deprived consortia of Coccomyxa chodatii and Rhodobium gokarnense at dim and high light

In this work, tuning oxygen tension was targeted to improve hydrogen evolution. To achieve such target, various consortia of the chlorophyte Coccomyxa chodatii with a newly isolated photosynthetic purple non-sulfur bacterium (PNSB) strain Rhodobium gokarnense were set up, sulfur replete/deprived, malate/acetate fed, bicarbonate/sulfur added at dim/high light. C. chodatii and R. gokarnense are newly introduced to biohydrogen studies for the first time. Dim light was applied to avoid the inhibitory drawbacks of photosynthetic oxygen evolution, values of hydrogen are comparable with high light or even more and thus economically feasible to eliminate the costs of artificial illumination. Particularly, the consortium of 2n− (n = 1.9 × 105 cell/ml, sulfur deprived) demonstrated its perfection for the target, i.e., the highest possible cumulative hydrogen. This consortium exhibited negative photosynthesis, i.e., oxygen uptake in the light. Most hydrogen in consortia is from bacterial origin, although algae evolved much more hydrogen than bacteria on per cell basis, but for only one day (the second 24 h), as kinetics revealed. The higher hydrogen in unibacterial culture or consortia results from higher bacterial cell density (20 times). Consortia evolved more hydrogen than their respective separate cultures, further enhanced when bicarbonate and sulfur were supplemented at higher light. The share of algae relatively increased as bicarbonate or sulfur were added at higher light intensity, i.e., PSII activity partially recovered, resulting in a transient autotrophic hydrogen evolution. The addition of acetic acid in mixture with malic acid significantly enhanced the cumulative hydrogen levels, mostly decreased cellular ascorbic acid indicating less oxidative stress and relief of PSII, relative to malic acid alone. Starch, however, decreased, indicating the specificity of acetic acid. Exudates (reducing sugars, amino acids, and soluble proteins) were detected, indicating mutual utilization. Yet, hydrogen evolution is limited; tuning PSII activity remains a target for sustainable hydrogen production.

Combined effect of bicarbonate and water in photosynthetic oxygen evolution and carbon neutrality

Combined effect of bicarbonate and water in photosynthetic oxygen evolution and carbon neutrality

Physiological Responses of a Diazotrophic Cyanobacterium to Acidification of Paddy Floodwater: N2 Fixation, Photosynthesis, and Oxidative-Antioxidative Characteristics.

Long-term of excessive fertilization using nitrogen (N) chemical fertilizer caused the acidification of paddy soils. Presently, the impacts of soil acidification on physiological characteristics of diazotrophic cyanobacteria remain unknown. In order to elucidate this issue, the effects of paddy floodwater acidification on activities of respiration, photosynthetic oxygen evolution, and N2 fixation of a paddy diazotrophic cyanobacterium Aliinostoc sp. YYLX235 were investigated in this study. In addition, the origination and quenching of intracellular reactive oxygen species (ROS) were analyzed. The acidification of paddy floodwater decreased intracellular pH and interfered in energy flux from light-harvesting chlorophyll antenna to the reaction center of photosystem II (PS II). Activities of respiration, photosynthetic oxygen evolution, and N2 fixation were decreased by the acidification of paddy floodwater. Accompanied with an increase in ROS, the level of antioxidative system increased. Superoxide dismutase (SOD) and catalase (CAT) were the main enzymatic ROS scavengers in the cells of YYLX235; reduced glutathione (GSH) was the main non-enzymatic antioxidant. Antioxidants and oxidants in the cells of YYLX235 lost balance when the pH of paddy floodwater fell to 5.0 and 4.0, and lipid oxidative damage happened. The results presented in this study suggest that the acidification of paddy soil severely interfered in the photosynthesis of diazotrophic cyanobacteria and induced the production of ROS, which in turn resulted in oxidative damage on diazotrophic cyanobacteria and a decrease in cell vitality.

Utilization of light energy and photodynamic therapy based on thylakoid membranes

<p indent="0mm">The thylakoid membrane, which contains photosynthetic pigments, lipids and proteins, is the main site where the photosynthetic light reaction of green plants, eukaryotic algae and cyanobacteria occurs. Water photolysis and photosynthetic electron transport are two core processes of the light reaction. The former is responsible for converting photons into electrons, and the latter then condenses the energy from the high-potential electrons into energy carriers such as adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide phosphate (NADPH). Due to the electron transport and energy conversion properties of the light reaction, thylakoid membrane can be used in biophotoelectrochemical and biophotoelectrocatalytic systems. Biophotoelectrochemical systems refer to direct or indirect extraction of electrons from the photosynthetic electron transfer chain (PETC) of the thylakoid membrane and transfer the electrons into an external electrode, eventually converting light energy into electric current. Biophotoelectrocatalytic systems refer to the use of ATP and NADPH generated in the light reaction of the thylakoid membrane to drive a series of ATP- or NADPH-dependent biocatalytic reactions. These thylakoid membrane-based light energy utilization systems are featured with material renewability and environmental compatibility. In addition, they show higher energy efficiency than that of the whole photosynthetic-cell systems. Furthermore, thylakoid membranes also hold clear advantages over sub-cellular photosystems, including retention of photosynthetic complexes in their natural environment and relatively simple and fast procedures for their extraction and purification. For biophotoelectrochemical systems, scientists have optimized the electron transfer between the thylakoid membrane and electrode, for example by developing different immobilization methods, or modifying electrode surface with redox polymers and nanomaterials. As an effective platform for cofactor regeneration, the thylakoid membrane-based biophotoelectrocatalytic systems have been used to drive the enzymatic synthesis of poly(3-hydroxybutyrate) (PHB) from acetate, as well as CO₂ fixation through a synthetic crotonyl-coenzyme A (CoA)/ethylmalonyl-CoA/hydroxybutyryl-CoA (CETCH) cycle. In addition to light energy utilization, thylakoid membranes can also be used in photodynamic therapy (PDT) of tumors. Firstly, the photosensitizer porphyrin in the chlorophyll molecules can produce singlet oxygen (¹O₂) from O₂ under visible light irradiation, which in turn kills the tumor cells. Secondly, the photosynthetic oxygen evolution of thylakoid membrane can rapidly supply O₂ <italic>in situ</italic>. Moreover, thylakoid membranes contain abundant catalase, which catalyzes the decomposition of H₂O₂ into O₂, thus further increasing the supply of O₂. This paper summarizes recent progress in the research of thylakoid membranes in these three fields, focusing on the application forms and underlying mechanisms. Moreover, the difficulties and challenges in the application of thylakoid membrane are discussed, and future research directions are prospected. Specifically, developing protective structures such as hydrogels or artificial vesicles to address the issue of short half-life of isolated thylakoid membranes will be crucial. In light of their ingenious energy conversion characteristics and amenability for potential commercialization, thylakoid membrane-based biotechnological systems will have a bright future in the fields of bioenergy, biocatalysis and biomedicine.

Effects of Novel Photosynthetic Inhibitor [CuL2]Br2 Complex on Photosystem II Activity in Spinach.

The effects of the novel [CuL2]Br2 complex (L = bis{4H-1,3,5-triazino [2,1-b]benzothiazole-2-amine,4-(2-imidazole)}copper(II) bromide complex) on the photosystem II (PSII) activity of PSII membranes isolated from spinach were studied. The absence of photosynthetic oxygen evolution by PSII membranes without artificial electron acceptors, but in the presence of [CuL2]Br2, has shown that it is not able to act as a PSII electron acceptor. In the presence of artificial electron acceptors, [CuL2]Br2 inhibits photosynthetic oxygen evolution. [CuL2]Br2 also suppresses the photoinduced changes of the PSII chlorophyll fluorescence yield (FV) related to the photoreduction of the primary quinone electron acceptor, QA. The inhibition of both characteristic PSII reactions depends on [CuL2]Br2 concentration. At all studied concentrations of [CuL2]Br2, the decrease in the FM level occurs exclusively due to a decrease in Fv. [CuL2]Br2 causes neither changes in the F0 level nor the retardation of the photoinduced rise in FM, which characterizes the efficiency of the electron supply from the donor-side components to QA through the PSII reaction center (RC). Artificial electron donors (sodium ascorbate, DPC, Mn2+) do not cancel the inhibitory effect of [CuL2]Br2. The dependences of the inhibitory efficiency of the studied reactions of PSII on [CuL2]Br2 complex concentration practically coincide. The inhibition constant Ki is about 16 µM, and logKi is 4.8. As [CuL2]Br2 does not change the aromatic amino acids’ intrinsic fluorescence of the PSII protein components, it can be proposed that [CuL2]Br2 has no significant effect on the native state of PSII proteins. The results obtained in the present study are compared to the literature data concerning the inhibitory effects of PSII Cu(II) aqua ions and Cu(II)-organic complexes.

Photosynthesis of Submerged and Surface Leaves of the Dwarf Water Lily (Nymphoides aquatica) Using PAM Fluorometry

Dwarf Water Lilies (Nymphoides aquatica (J.F. Gmel) Kuntze have floating and submerged leaves. Some submerged aquatic vascular plants have a form of CAM (Crassulacean Acid Metabolism) called Submerged Aquatic Macrophyte (SAM) metabolism. Blue-diode based PAM technology was used to measure the Photosynthetic Oxygen Evolution Rate (POER: 1O2 ≡ 4e– ). Optimum Irradiance (Eopt), maximum POER (POERmax) and quantum efficiency (α0) all vary on a diurnal cycle. The shape of the POER vs. E curves is different in seedling, submerged and surface leaves. Both Eopt and POERmax are very low in seedling leaves (Eopt ≈ 104 μmol photon m–2 s–1, PPFD; POERmax ≈ 4.95 µmol O2 g–1 Chl a s–1), intermediate in mature submerged leaves (Eopt ≈ 419 µmol photon m–2 s–1 PPFD, POERmax ≈ 38.1 µmol O2 g–1 Chl a s–1) and very high in surface leaves (Eopt ≈ 923 µmol photon m–2 s–1 PPFD, POERmax ≈ 76.1 µmol O2 g–1 Chl a s–1). Leaf titratable acid (C4 acid pool) is too small (≈20 to 50 mol H+ m–3) to support substantial SAM metabolism. Gross daily photosynthesis of surface leaves is ≈3.71 g C m–2 d–1 in full sun and as much as 1.4 gC m–2 d–1 in shaded submerged leaves. There is midday inhibition of photosynthesis.