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Far-Red Spectrum of Second Emerson Effect: A Study Using Dual-Wavelength Pulse Amplitude Modulation Fluorometry
摘要： Non-additive enhancement of the photosynthesis excited by simultaneous illumination with far-red light and light of shorter wavelengths is called as “second Emerson effect”. Its action spectra are well-known as a photosynthetic yield’s dependence on light wavelength in red (630-690 nm) spectral region at a constant-wavelength far-red illumination near 700-715 nm. However, the opposite dependence of the photosynthetic yield’s of shorter constant-wavelength light (red or blue) on light wavelength in far-red (690-760 nm) spectral region was never studied. In this study the action spectrum of second Emerson effect was studied using a fast-Fourier dual-wavelength Pulse Amplitude Modulation (PAM) fluorometry. Chlorophyll fluorescence in ailanthus (Ailanthus altissima Mill.) leaves was excited with blue modulated light. Far-red induced decrease of fluorescence (fluorescence shift-FRIFS) was studied in response to illumination of leaves with a background light from 690 to 760 nm (10 nm step), calculating FRIFS = (F0-Fs)/F0, where F0-fluorescence measured without and Fs-with far-red light. Maximum FRIFS was observed at 720 nm (11.8%), but it still remained considerable at 740, 750 nm and a low FRIFS values were revealed at 690 and even at 760 nm. Measurements carried out with blue saturating flashes during and after far-red illumination showed the increase of quantum yield of Photosystem II (PSII), calculated as Fv/Fm at 720 nm background light. FRIFS had lower values under excitation with red modulating light. It is concluded that FRIFS is a result of a photochemical quenching caused by an additional selective far-red excitation of PSI in conditions when PSII is preferably excited by blue light thus leading the PSI to limit non-cyclic electron flow. The contradiction between the known absorption spectra of PSI-light harvesting complex I and the observed action spectrum of second Emerson effect (FRIFS spectrum) is discussed.
关键词： Photosystem II,Ailanthus Altissima,Photosystem I,Second Emerson Effect,Fast-Fourier PAM-Fluorometry,Far-Red Light,Thylakoid Electron Transport
更新于2025-11-14 15:30:11
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Theoretical Model of Exciton States and Ultra-fast Energy Transfer in Heliobacterial Type-I Homodimeric Reaction Center
摘要： A simple theoretical model of exciton dynamics was proposed to interpret the fast excitation energy transfer process in the Type-I homodimeric reaction center of Heliobacterium modesticaldum (hRC); this structure was recently identified and shown to resemble that of the plant/cyanobacterial photosystem I (PSI) reaction center. The exciton state model, which mainly relies on the geometries of 54 bacteriochlorophyll (BChl) g, 4 BChl-g′ and 2 chlorophyll (Chl) a on hRC and assumes constant site energy values for the pigments, reproduced the absorption spectrum of hRC rather well. The model also enabled numerical analysis of the exciton dynamics on hRC, which can be compared with the decay-associated spectra obtained by the laser spectroscopy experiments. The model indicates that the stronger transition-dipole moment on BChl-g contributes to the faster energy transfer due to the higher coherency of the delocalized exciton states on hRC compared to that on PSI that arranges Chl-a at almost homologous locations.
关键词： chlorophyll,photosystem I,bacteriochlorophyll,exciton dynamics,energy transfer,reaction center
更新于2025-09-23 15:21:21
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Oxidation of P700 Ensures Robust Photosynthesis
摘要： In the light, photosynthetic cells can potentially suffer from oxidative damage derived from reactive oxygen species. Nevertheless, a variety of oxygenic photoautotrophs, including cyanobacteria, algae, and plants, manage their photosynthetic systems successfully. In the present article, we review previous research on how these photoautotrophs safely utilize light energy for photosynthesis without photo-oxidative damage to photosystem I (PSI). The reaction center chlorophyll of PSI, P700, is kept in an oxidized state in response to excess light, under high light and low CO2 conditions, to tune the light utilization and dissipate the excess photo-excitation energy in PSI. Oxidation of P700 is co-operatively regulated by a number of molecular mechanisms on both the electron donor and acceptor sides of PSI. The strategies to keep P700 oxidized are diverse among a variety of photoautotrophs, which are evolutionarily optimized for their ecological niche.
关键词： photosynthesis,reactive oxygen species,photoinhibition,P700 oxidation,photosystem I
更新于2025-09-23 15:21:21
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Biotechnology for Biofuel Production and Optimization || Photobiohybrid Solar Conversion with Metalloenzymes and Photosynthetic Reaction Centers
摘要： Sunlight provides an abundant and sustainable supply of energy to the Earth's surface, at levels that far exceed the yearly human global energy demand. However, the intermittency and geographic variability of solar irradiation, combined with the need for storage, limits the ability to provide practical alternatives to use of conventional fossil fuels. To better utilize the available solar energy, current photovoltaic technologies must be integrated with conversion technologies that produce storable chemical energy (fuels) that are easily distributed to meet regional demand as needed. In biological photosynthesis, conversion of solar energy into chemical energy is accomplished by the water-splitting and CO2 fixation reactions. The molecular machinery of the natural system provides ideal models for the design and development of artificial solar-to-fuel systems. The theoretical limit of biological photosynthesis is ~12%, and under optimal conditions, efficiencies of 7% have been achieved; however, 1% is a more typical benchmark. Photosynthetic reactions rely on four key components which are integrated to act in concert as a highly functional energy transduction network: (i) the antenna, where photons are absorbed; (ii) the charge separation site, where high-energy excitons (electron-hole pairs) are separated into positive and negative charge carriers; (iii) the reduction catalyst, where electrons are utilized in a fuel-forming reaction (e.g., NAD+ → NADH formation used for CO2 fixation in photosynthesis); and (iv) the oxidation catalyst, where holes are utilized to drive an oxidation reaction (e.g., water oxidation by photosystem II during photosynthesis). Efforts are underway to translate photobiological design principles to develop artificial systems for solar fuel generation that circumvent or eliminate unwanted side reactions and attain higher efficiencies. These efforts include the development of photochemical devices, inorganic biomimetic and bioinspired catalysts and light-harvesting complexes, and organic hybrid materials for photo-driven fuel production. Here, we discuss research focused on the development of hybrid materials that incorporate artificial and natural molecular components into unified functional systems for light-harvesting and conversion into reduced chemical fuels.
关键词： solar conversion,photobiohybrid,metalloenzymes,CO2 reduction,hydrogen production,photosystem I,photosynthetic reaction centers
更新于2025-09-23 15:21:01
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Plasmonic enhancement of photocurrent generation in Photosystem Ia??based hybrid electrode
摘要： We experimentally demonstrate that oriented assembly of red algal photosystem I (PSI) reaction center on a plasmonically active Silver Island Film (SIF) leads to strong enhancement of both fluorescence intensity and photocurrent generated upon illumination. PSI complexes were specifically attached to a monolayer of graphene deposited on the SIF layer. The results of comprehensive fluorescence microscopy point out to the critical role of the SIF layer in enhancing the optical response of PSI, as we observe increased emission intensity. Hence, importantly, the strong increase of photocurrent generation demonstrated for the biohybrid electrodes, can be directly associated with the plasmonic enhancement of optical and electrochemical functionalities of PSI. The results also indicate that the graphene layer is not diminishing the influence of the plasmonic excitations in SIF on the absorption and emission of PSI.
关键词： hybrid electrode,plasmonic enhancement,Photosystem I,graphene,Silver Island Film,photocurrent generation
更新于2025-09-23 15:19:57
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Photovoltaic activity of electrodes based on intact photosystem I electrodeposited on bare conducting glass
摘要： We demonstrate photovoltaic activity of electrodes composed of fluorine-doped tin oxide (FTO) conducting glass and a multilayer of trimeric photosystem I (PSI) from cyanobacterium Synechocystis sp. PCC 6803 yielding, at open circuit potential (OCP) of + 100 mV (vs. SHE), internal quantum efficiency of (0.37 ± 0.11)% and photocurrent density of up to (0.5 ± 0.1) μA/cm2. The photocurrent measured for OCP is of cathodic nature meaning that preferentially the electrons are injected from the conducting layer of the FTO glass to the photooxidized PSI primary electron donor, P700+, and further transferred from the photoreduced final electron acceptor of PSI, Fb, via ascorbate electrolyte to the counter electrode. This observation is consistent with preferential donor-side orientation of PSI on FTO imposed by applied electrodeposition. However, by applying high-positive bias (+ 620 mV) to the PSI-FTO electrode, exceeding redox midpoint potential of P700 (+ 450 mV), the photocurrent reverses its orientation and becomes anodic. This is explained by “switching off” the natural photoactivity of PSI particles (by the electrochemical oxidation of P700 to P700+) and “switching on” the anodic photocurrent from PSI antenna Chls prone to photooxidation at high potentials. The efficient control of the P700 redox state (P700 or P700+) by external bias applied to the PSI-FTO electrodes was evidenced by ultrafast transient absorption spectroscopy. The advantage of the presented system is its structural simplicity together with in situ-proven high intactness of the PSI particles.
关键词： Photoelectrochemical measurements,Cyanobacterium Synechocystis sp. PCC 6803,Femtosecond-transient absorption,Photovoltaics,FTO conducting glass,Photosystem I
更新于2025-09-19 17:13:59
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Structure of a cyanobacterial photosystem I tetramer revealed by cryo-electron microscopy
摘要： Photosystem I (PSI) functions to harvest light energy for conversion into chemical energy. The organisation of PSI is variable depending on the species of organism. Here we report the structure of a tetrameric PSI core isolated from a cyanobacterium, Anabaena sp. PCC 7120, analysed by single-particle cryo-electron microscopy (cryo-EM) at 3.3 ? resolution. The PSI tetramer has a C2 symmetry and is organised in a dimer of dimers form. The structure reveals interactions at the dimer-dimer interface and the existence of characteristic pigment orientations and inter-pigment distances within the dimer units that are important for unique excitation energy transfer. In particular, characteristic residues of PsaL are identified to be responsible for the formation of the tetramer. Time-resolved fluorescence analyses showed that the PSI tetramer has an enhanced excitation-energy quenching. These structural and spectroscopic findings provide insights into the physiological significance of the PSI tetramer and evolutionary changes of the PSI organisations.
关键词： cyanobacterium,excitation energy transfer,tetramer,Photosystem I,cryo-electron microscopy
更新于2025-09-11 14:15:04