Optically Matched Semiconductor Quantum Dots Improve Photophosphorylation Performed by Chloroplasts

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

Ultrafast spectroscopy studies on the mechanism of electron transfer and energy conversion in the isolated pseudo ginseng, water hyacinth and spinach chloroplasts

The spectroscopy characteristics and the fluorescence lifetime for the chloroplasts isolated from the pseudo ginseng, water hyacinth and spinach plant leaves have been studied by absorption spectra, low temperature steady-state fluorescence spectroscopy and single photon counting measurement under the same conditions and by the same methods. The similarity of the absorption spectra for the chloroplasts at room temperature suggests that different plants can efficiently absorb light of the same wavelength. The fluorescence decays in PS II measured at the natural QA state for the chloroplasts have been fitted by a three-exponential kinetic model. The three fluorescence lifetimes are 30, 274 and 805 ps for the pseudo ginseng chloroplast; 138, 521 and 1494 ps for the water hyacinth chloroplast; 197, 465 and 1459 ps for the spinach chloroplast, respectively. The slow lifetime fluorescence component is assigned to a collection of associated light harvesting Chl a/b proteins, the fast lifetime component to the react     

Efficient Light‐Harvesting Systems with Tunable Emission through Controlled Precipitation in Confined Nanospace

Light harvesting is a key step in photosynthesis but creation of synthetic light‐harvesting systems (LHSs) with high efficiencies has been challenging. When donor and acceptor dyes with aggregation‐induced emission were trapped within the interior of cross‐linked reverse vesicles, LHSs were obtained readily through spontaneous hydrophobically driven aggregation of the dyes in water. Aggregation in the confined nanospace was critical to the energy transfer and the light‐harvesting efficiency. The efficiency of the excitation energy transfer (EET) reached 95 % at a donor/acceptor ratio of 100:1 and the energy transfer was clearly visible even at a donor/acceptor ratio of 10 000:1. Multicolor emission was achieved simply by tuning the donor/acceptor feed ratio in the preparation and the quantum yield of white light emission from the system was 0.38, the highest reported for organic materials in water to date.     

CHLOROPLAST PIGMENTS and THEIR BIOSYNTHESIS IN RELATION TO LIGHT INTENSITY*

Abstract— Depending on the light intensity that they received during growth, radish seedlings altered not only the pigment and quinone composition of the thylakoid membrane but also the chloroplast ultrastructure. In strong light, sun chloroplasts of radish were very similar to those from sun leaves of beech trees, while those developed under under dim light possessed a typical shade chloroplast. Radish shade chloroplasts contained a higher chlorophyll content and a higher concentration of xanthophylls resulting in a lower xanthophyll to carotene ratio as compared to sun chloroplasts. Chloroplasts from radish grown in strong light showed a much higher activity in their terpenoid metabolism than plastids from shade plants. Chlorophylls and carotenoids which are involved in the absorption of light and the transfer of energy during photosynthesis were labeled by [³H]-mevalonate to a much higher degree in plastids from sun leaves as compared to plastids from shade leaves. This shows that in strong light where pigments are continuously broken down and resynthesized in order to maintain photosynthesis, chlorophylls and carotenoids exhibit a much higher turnover rate than the pigments of shade plants.     

Conjugated Polymer Nanoparticles with Appended Photo‐Responsive Units for Controlled Drug Delivery,Release, and Imaging

Carriers that can afford tunable physical and structural changes are envisioned to address critical issues in controlled drug delivery applications. Herein, photo‐responsive conjugated polymer nanoparticles (CPNs) functionalized with donor–acceptor Stenhouse adduct (DASA) and folic acid units for controlled drug delivery and imaging are reported. Upon visible‐light (λ=550 nm) irradiation, CPNs simultaneously undergo structure, color, and polarity changes that release encapsulated drugs into the cells. The backbone of CPNs favors FRET to DASA units boosting their fluorescence. Notably, drug‐loaded CPNs exhibit excellent biocompatibility in the dark, indicating perfect control of the light trigger over drug release. Delivery of both hydrophilic and hydrophobic drugs with good loading efficiency was demonstrated. This strategy enables remotely controlled drug delivery with visible‐light irradiation, which sets an example for designing delivery vehicles for non‐invasive therapeutics.     

Conjugated Polymer Nanoparticles with Appended Photo‐Responsive Units for Controlled Drug Delivery,Release, and Imaging

Carriers that can afford tunable physical and structural changes are envisioned to address critical issues in controlled drug delivery applications. Herein, photo‐responsive conjugated polymer nanoparticles (CPNs) functionalized with donor–acceptor Stenhouse adduct (DASA) and folic acid units for controlled drug delivery and imaging are reported. Upon visible‐light (λ=550 nm) irradiation, CPNs simultaneously undergo structure, color, and polarity changes that release encapsulated drugs into the cells. The backbone of CPNs favors FRET to DASA units boosting their fluorescence. Notably, drug‐loaded CPNs exhibit excellent biocompatibility in the dark, indicating perfect control of the light trigger over drug release. Delivery of both hydrophilic and hydrophobic drugs with good loading efficiency was demonstrated. This strategy enables remotely controlled drug delivery with visible‐light irradiation, which sets an example for designing delivery vehicles for non‐invasive therapeutics.     

Blue light-induced chloroplast reorientations in Lemna trisulca L. (duckweed) are controlled by two separable cellular mechanisms as suggested by different sensitivity to wortmannin

Chloroplast reorientations within mesophyll cells are among the most rapid physiological responses of higher plants to blue light. At light intensities below the saturation point of photosynthesis, chloroplasts move to the cell walls perpendicular to the direction of light and maximize light absorption (low-fluence rate response [LFR]). At light intensities above the saturation point of photosynthesis, chloroplasts redistribute to cell walls parallel to the direction of light (high-fluence rate response [HFR]). The actin-based mechanism is responsible for the light-induced chloroplast movements. We have found that an inhibitor of phosphoinositide-3-kinases, wortmannin, potently and irreversibly inhibited LFR and HFR chloroplast responses to blue light in Lemna trisulca L. mesophyll cells. Microscopic observations and photometric measurement indicated that 100 nM wortmannin specifically inhibited LFR in Lemna, whereas HFR displayed no sensitivity to the inhibitor at this concentration. A complete inhibition of the HFR could be obtained by 1 microM wortmannin. These data indicate that LFR is more sensitive to wortmannin than HFR and suggest that these two responses may be under the control of different cellular mechanisms. Our results suggest that phosphoinositide kinases and other phosphoinositide cycle enzymes may play a role in the transduction of the light signal to the actin cytoskeleton in Lemna as factors specifying the direction of chloroplast movements. A hypothetical model assuming three signaling pathways regulating light-induced chloroplast reorientations in mesophyll cells is proposed.     

Peroxidative reactions attenuate oxygen effect on spectroscopic properties of isolated chloroplasts.

Steady-state absorption and fluorescence excitation spectra have been measured at 25 degrees C in order to elucidate the differences between isolated chloroplasts from pea (chilling-sensitive plant) and bean (chilling-tolerant plant) and their response to oxygen treatment. A weaker light harvesting in bean in comparison with pea chloroplasts is related to higher free fatty acids level and extended peroxidation activities of bean chloroplasts. Peroxidation of free fatty acids in bean chloroplasts results in an accumulation of oxygenated forms of fatty acids demonstrated by a large negative band around 400 nm in absorption difference spectra, while the excitation spectra are not significantly altered. Similar changes have been observed in the lipase-treated pea chloroplasts. In contrast, in both pea and bean chloroplasts exhibiting no peroxidation due to antimycin A treatment, oxygen induces a pronounced absorbance increase in the regions around 435, 470 and 674 nm indicating the chloroplast swelling. A decline of chlorophyll fluorescence excitation caused by oxygen, may result from a decrease in energy transfer from antennae complexes to chlorophyll species emitting at both 680 and 740 nm. The oxygen-induced changes are partially reversed upon restoration of anaerobic conditions. The presented data show for the first time, that in contrast to pea chloroplasts the peroxidation abolishes an oxygen-induced decrease in light harvesting in bean chloroplasts, i.e., a chilling-sensitive plant.     

Chlorophyll

Chlorophyll exists since ca. 3 billion years and is at begin of the evolution. This chiral, green Mg‐porphyrin‐complex absorbs as a photosensitizer in the antennas of the light‐harvesting complexes of chloroplasts all parts of visible light except of green light. This energy is transferred to the reaction centres of oxygenic photosynthesis. By this redox reaction carbon dioxide and water are transformed into carbohydrates and oxygen. We describe how the structures of chlorophylls were elucidated, discuss structure‐property relations, the relationship to heme of blood, everyday uses, and how Green has influenced our language. The isolation of pure chlorophyll a from spinach is an experimental challenge, which we report in detail. All analytical spectra were recorded and are reproduced and interpreted either in the main part or in the supporting information.     

REGULATION OF CHLOROPLAST DEVELOPMENT BY RED AND BLUE LIGHT

There are specific differences between red and blue light greening of etiolated seedlings of Hordevm vulgare L. Blue light results in a different prenyl lipid composition of chloroplast as compared to red light of equal quanta density. This is documented by a much higher prenylquinone content, higher chlorophyll a/b ratios, and lower values for the ratio xanthophylls to carotenes (x/c). The photosynthetic activity of “blue light” chloroplasts (Hill reaction) is higher than that of “red light” chloroplasts. These differences in prenylquinone composition and Hill-activity are associated with a different ultrastructure of chloroplasts. “Red light” chloroplasts exhibit a much higher grana content than “blue light” chloroplasts. The difference in thylakoid composition, photosynthetic activity and chloroplast structure found between blue and red light greening are similar to those found between sun and shade leaves and those between plants grown under high and low light intensities.     

Artificial photosynthesis by using chloroplasts from spinach adsorbed on a nanocrystalline TiO2 electrode for photovoltaic conversion

Photovoltaic conversion has been achieved by use of chloroplasts (photosynthetic organs) from spinach adsorbed on a nanocrystalline TiO₂ film on an indium tin oxide (ITO) glass electrode (chloroplast/TiO₂ electrode). The shape of the absorption spectrum of the chloroplast/TiO₂ electrode is almost the same that of a dispersion of the chloroplasts. Absorption maxima of the chloroplast/TiO₂ electrode observed at 430, 475, and 670 nm were attributed to carotenoid and chlorophyll molecules, suggesting that chloroplasts have been adsorbed by the nanocrystalline TiO₂ film on the ITO electrode. The photocurrent responses of chloroplast/TiO₂ electrodes were measured by using a solution of 0.1 M tetrabutylammonium hexafluorophosphate in acetonitrile as redox electrolyte in the presence or absence of water and 100 mW cm^?2 irradiation. The photocurrent of the chloroplast/TiO₂ electrode was increased by adding water to the redox electrolyte. The photocurrent responses of chloroplast/TiO₂ electrodes irradiated with monochromatic light (680 nm, the absorption band of photosystem II complexed with evolved oxygen) were measured by use of a solution of 0.1 M tetrabutylammonium hexafluorophosphate in acetonitrile as redox electrolyte in the presence or absence of water. A chloroplast/TiO₂ electrode photocurrent was observed only when the redox electrolyte containing water was used, indicating that the oxygen evolved from water by photosystem II in chloroplasts adsorbed by a nanocrystalline TiO₂ film on an ITO electrode irradiated at 680 nm is reduced to water by the catalytic activity of the platinum electrode. The maximum incident photon-to-current conversion efficiency (IPCE) was 0.8 % on irradiation at 670 nm.     

Photoelectrochemical Complexes of Fucoxanthin‐Chlorophyll Protein for Bio‐Photovoltaic Conversion with a High Open‐Circuit Photovoltage

Open‐circuit photovoltage (V_oc ) is among the critical parameters for achieving an efficient light‐to‐charge conversion in existing solar photovoltaic devices. Natural photosynthesis exploits light‐harvesting chlorophyll (Chl) protein complexes to transfer sunlight energy efficiently. We describe the exploitation of photosynthetic fucoxanthin‐chlorophyll protein (FCP) complexes for realizing photoelectrochemical cells with a high V_oc . An antenna‐dependent photocurrent response and a V_oc up to 0.72 V are observed and demonstrated in the bio‐photovoltaic devices fabricated with photosynthetic FCP complexes and TiO₂ nanostructures. Such high V_oc is determined by fucoxanthin in FCP complexes, and is rarely found in photoelectrochemical cells with other natural light‐harvesting antenna. We think that the FCP‐based bio‐photovoltaic conversion will provide an opportunity to fabricate environmental benign photoelectrochemical cells with high V_oc , and also help improve the understanding of the essential physics behind the light‐to‐charge conversion in photosynthetic complexes.     

Dual selective nitration in Arabidopsis: Almost exclusive nitration of PsbO and PsbP,and highly susceptible nitration of four non‐PSII proteins,including peroxiredoxin II E

Protein tyrosine nitration is a selective process, as revealed in studies of animals. However, evidence for selective protein nitration in plants is scarce. In this study, Arabidopsis plants were exposed to air with or without nitrogen dioxide at 40 ppm for 8 h in light. Proteins extracted from whole leaves or isolated chloroplasts were subjected to 2D PAGE followed by SYPRO Ruby staining and immunoblotting using an anti‐3‐nitrotyrosine antibody. We determined the relative intensity of a spot on an immunoblot (designated RISI), and relative intensity of the corresponding spot on SYPRO Ruby gel (designated RISS). Proteins that exhibited a high RISI value and/or a high RISI/RISS ratio were considered selectively nitrated. In whole leaf proteins from exposed plants, all immunopositive spots were identified as PsbO1, PsbO2 or PsbP1 by PMF. Thus, nitration was exclusive to PsbO and PsbP, extrinsic proteins of photosystem II (PSII). Their RISI/RISS ratio was ≤1.5. Non‐exposed plants showed very faint nitration. In purified chloroplast proteins, PsbO and PsbP accounted for >80% of the total RISI values, while four non‐PSII proteins, including peroxiredoxin II E, exhibited high RISI/RISS ratios (2.5～6.6). Tyr⁹ of PsbO1 was identified as a nitration site. Thus, nitration is selective for two PSII and four non‐PSII proteins in Arabidopsis.     

Polydopamine as a Biomimetic Electron Gate for Artificial Photosynthesis

We report on the capability of polydopamine (PDA), a mimic of mussel adhesion proteins, as an electron gate as well as a versatile adhesive for mimicking natural photosynthesis. This work demonstrates that PDA accelerates the rate of photoinduced electron transfer from light‐harvesting molecules through two‐electron and two‐proton redox‐coupling mechanism. The introduction of PDA as a charge separator significantly increased the efficiency of photochemical water oxidation. Furthermore, simple incorporation of PDA ad‐layer on the surface of conducting materials, such as carbon nanotubes, facilitated fast charge separation and oxygen evolution through the synergistic effect of PDA‐mediated proton‐coupled electron transfer and the high conductivity of the substrate. Our work shows that PDA is an excellent electron acceptor as well as a versatile adhesive; thus, PDA constitutes a new electron gate for harvesting photoinduced electrons and designing artificial photosynthetic systems.     

ORIENTATION MOVEMENTS OF CHLOROPLASTS IN Vallisneria EPIDERMAL CELLS: DIFFERENT EFFECTS OF LIGHT AT LOW- and HIGH-FLUENCE RATE*

Abstract— Epidermal cells of Vallisneria gigantea have a large central vacuole which is surrounded by a thin layer of cytoplasm. The chloroplasts are distributed over all six cytoplasmic layers of an approximate cuboid. In low-intensity light, the accumulation of chloroplasts in the side facing the outer periclinal wall (the P side) continues for several hours. Red light (650 nm) shows the highest effect and induces such an accumulation even at a fluence rate of only 0.02 W/m². In response to high-intensity light, the chloroplasts move to the sides that face the anticlinal walls (the A sides) within a few tens of minutes. Blue light (450 nm) is most effective in inducing this movement. At a fluence rate of 1.51 W/m², the reaction is induced in only half of the specimens. Neither red nor blue light can induce any orientation movement in the presence of 100 μg/ml of cytochalasin B. The chloroplast movements in the P side have been examined with a time-lapse video system. When cells, in which the chloroplast accumulation has been completed after red-light irradiation, are subsequently irradiated with blue light, the rapid movement of chloroplasts to A sides is induced. However, a considerable number of chloroplasts remains in the center of the P side. The same is true of cells in which the chloroplasts have not accumulated in the P side because of cytochalasin B treatment during red-light irradiation, when such cells are irradiated with blue light after removal of the drug. Some anchoring mechanism seems to work in low-intensity light to render the chloroplasts immobile in the P side.     

PHOTOINHIBITION OF CHLOROPLAST REACTIONS

Abstract— An attemlpt was made to localize the site of photoinhibition of photosynthesis by measuring the decay of various chloroplast reactions after exposure to very strong light. A11 substrate reductions coupled to oxygen evolution as well as photophosphorylation mediated by PMS, proved equally sensitive to photoinhibition. Reactions involving only the long wave photosystem, such as TPN reduction with ascorbate as electron donor and photooxidation of cytochromec by detergent-treated chloroplasts were sensitive to a lower degree.
Photoinhibition irreversibly annihilated the 'variable' fraction of fluorescence emission —it decreased the steady state yield 2-3 fold and abolished the slow rise of the emission at the onset of illurnination.
It is concluded that the primary site of light inactivation is in, or close to, the trapping centers of the oxygen evolving step of photosynthesis. Pre-illumination leaves these traps in a state capable of draining light from sensitizing pigments but unable to perform useful photochemistry.     

Tuning the Triplet–Triplet Energy Transfer Between Phthalocyanine and Carotenoid by Methyl Groups on the Conjugated Chain

Mimicking light‐harvesting and photoprotective processes of natural photosynthesis by artificial supramolecular systems is of considerable interest for artificial photosynthesis. The authors of the highlighted paper report on synthesis and spectroscopic characterization of a novel Pd‐phthalocyanine–carotenoid dyads that allow to directly follow the triplet–triplet energy transfer between Pd‐phthalocyanine and carotenoid. Unexpectedly, the T‐T energy transfer does not follow the dependence on conjugation length of the acceptor carotenoid. Instead, the donor–acceptor coupling and resulting T‐T energy transfer rate is controlled by the presence or absence of a methyl groups on the conjugated chain in the vicinity of the carotenoid keto‐oxygen. This reveals yet another level of tuning the spectroscopic properties of carotenoids having a conjugated keto group in their structure, underlining their potential for tailoring specific supramolecular complexes carrying out either light‐harvesting or photoprotective functions.     

A Complex Comprising a Cyanine Dye Rotaxane and a Porphyrin Nanoring as a Model Light‐Harvesting System

A nanoring‐rotaxane supramolecular assembly with a Cy7 cyanine dye (hexamethylindotricarbocyanine) threaded along the axis of the nanoring was synthesized as a model for the energy transfer between the light‐harvesting complex LH1 and the reaction center in purple bacteria photosynthesis. The complex displays efficient energy transfer from the central cyanine dye to the surrounding zinc porphyrin nanoring. We present a theoretical model that reproduces the absorption spectrum of the nanoring and quantifies the excitonic coupling between the nanoring and the central dye, thereby explaining the efficient energy transfer and demonstrating similarity with structurally related natural light‐harvesting systems.     

Aqueous Platinum(II)‐Cage‐Based Light‐Harvesting System for Photocatalytic Cross‐Coupling Hydrogen Evolution Reaction

Photosynthesis is a process wherein the chromophores in plants and bacteria absorb light and convert it into chemical energy. To mimic this process, an emissive poly(ethylene glycol)‐decorated tetragonal prismatic platinum(II) cage was prepared and used as the donor molecule to construct a light‐harvesting system in water. Eosin Y was chosen as the acceptor because of its good spectral overlap with that of the metallacage, which is essential for the preparation of light‐harvesting systems. Such a combination showed enhanced catalytic activity in catalyzing the cross‐coupling hydrogen evolution reaction, as compared with eosin Y alone. This study offers a pathway for using the output energy from the light‐harvesting system to mimic the whole photosynthetic process.     

Light Harvesting and White‐Light Generation in a Composite of Carbon Dots and Dye‐Encapsulated BSA‐Protein‐Capped Gold Nanoclusters

Several strategies have been adopted to design an artificial light‐harvesting system in which light energy is captured by peripheral chromophores and it is subsequently transferred to the core via energy transfer. A composite of carbon dots and dye‐encapsulated BSA‐protein‐capped gold nanoclusters (AuNCs) has been developed for efficient light harvesting and white light generation. Carbon dots (C‐dots) act as donor and AuNCs capped with BSA protein act as acceptor. Analysis reveals that energy transfer increases from 63 % to 83 % in presence of coumarin dye (C153), which enhances the cascade energy transfer from carbon dots to AuNCs. Bright white light emission with a quantum yield of 19 % under the 375 nm excitation wavelength is achieved by changing the ratio of components. Interesting findings reveal that the efficient energy transfer in carbon‐dot–metal‐cluster nanocomposites may open up new possibilities in designing artificial light harvesting systems for future applications.