Redesign of the Chlamydomonas reinhardtii Q binding niche reveals photosynthesis works in the absence of a driving force for Q-Q electron transfer.

An in silico redesign of the secondary quinone electron acceptor (Q) binding pocket of the D1 protein of Photosystem II (PSII) suggested that mutations of the F265 residue would affect atrazine binding. Chlamydomonas reinhardtii mutants F265T and F265S were produced to obtain atrazine-hypersensitive strains for biosensor applications, and the mutants were indeed found to be more atrazine-sensitive than the reference strain IL. Fluorescence and thermoluminescence data agree with a weak driving force and confirm slow electron transfer but cannot exclude an additional effect on protonation of the secondary quinone.

Nanodiamond Particles Reduce Oxidative Stress Induced by Methyl Viologen and High Light in the Green Alga .

Widely used in biomedical and bioanalytical applications, the detonation nanodiamonds (NDs) are generally considered to be biocompatible and non-toxic to a wide range of eukaryotic cells. Due to their high susceptibility to chemical modifications, surface functionalisation is often used to tune the biocompatibility and antioxidant activity of the NDs. The response of photosynthetic microorganisms to redox-active NDs is still poorly understood and is the focus of the present study.

Acclimation Response of Green Microalgae Chlorella Sorokiniana to 2,3',4,4',6-Pentachlorobiphenyl.

The effect of the toxicant 2,3',4,4',6-pentachlorobiphenyl (PCB-119) on the growth, chlorophyll content, and PSII activity of C. sorokiniana cells was investigated. A strong negative effect of the toxicant was observed at PCB concentration of 0.

Single-walled carbon nanotubes protect photosynthetic reactions in Chlamydomonas reinhardtii against photoinhibition.

Single-walled carbon nanotubes (SWCNTs) are among the most exploited carbon allotropes in nanosensing, bioengineering, and photobiological applications, however, the interactions of nanotubes with the photosynthetic process and structures are still poorly understood. We found that SWCNTs are not toxic to the photosynthetic apparatus of the model unicellular alga Chlamydomonas reinhardtii and demonstrate that this carbon nanomaterial can protect algal photosynthesis against photoinhibition. The results show that the inherent phytotoxicity of the nanotubes may be overcome by an intentional selection of nanomaterial characteristics.

Mathematical Simulation of Electron Transport in the Primary Photosynthetic Processes.

Summarized results of investigation of regulation of electron transport and associated processes in the photosynthetic membrane using methods of mathematical and computer modeling carried out at the Department of Biophysics, Faculty of Biology, Lomonosov Moscow State University, are presented in this review. Detailed kinetic models of processes in the thylakoid membrane were developed using the apparatus of differential equations. Fitting of the model curves to the data of spectral measurements allowed us to estimate the values of parameters that were not determined directly in experiments.

Molecular, Brownian, kinetic and stochastic models of the processes in photosynthetic membrane of green plants and microalgae.

The paper presents the results of recent work at the Department of Biophysics of the Biological Faculty, Lomonosov Moscow State University on the kinetic and multiparticle modeling of processes in the photosynthetic membrane. The detailed kinetic models and the rule-based kinetic Monte Carlo models allow to reproduce the fluorescence induction curves and redox transformations of the photoactive pigment P700 in the time range from 100 ns to dozens of seconds and make it possible to reveal the role of individual carriers in their formation for different types of photosynthetic organisms under different illumination regimes, in the presence of inhibitors, under stress conditions. The fitting of the model curves to the experimental data quantifies the reaction rate constants that cannot be directly measured experimentally, including the non-radiative thermal relaxation reactions.

Simulating the Interplay between the Uptake of Inorganic Phosphate and the Cell Phosphate Metabolism under Phosphorus Feast and Famine Conditions in .

Using a mathematical simulation approach, we studied the dynamics of the green microalga phosphate metabolism response to shortage and subsequent replenishing of inorganic phosphate in the medium. A three-pool interaction model was used to describe the phosphate uptake from the medium, its incorporation into the cell organic compounds, its storage in the form of polyphosphates, and culture growth. The model comprises a system of ordinary differential equations.

State of the phycobilisome determines effective absorption cross-section of Photosystem II in Synechocystis sp. PCC 6803.

Quenching of excess excitation energy is necessary for the photoprotection of light-harvesting complexes. In cyanobacteria, quenching of phycobilisome (PBS) excitation energy is induced by the Orange Carotenoid Protein (OCP), which becomes photoactivated under high light conditions. A decrease in energy transfer efficiency from the PBSs to the reaction centers decreases photosystem II (PS II) activity.

Mapping Single Walled Carbon Nanotubes in Photosynthetic Algae by Single-Cell Confocal Raman Microscopy.

Carbon nanotubes (CNTs) are among the most exploited carbon allotropes in the emerging technologies of molecular sensing and bioengineering. However, the advancement of algal nanobiotechnology and nanobionics is hindered by the lack of methods for the straightforward visualization of the CNTs inside the cell. Herein, we present a handy and label-free experimental strategy based on visible Raman microscopy to assess the internalization of single-walled carbon nanotubes (SWCNTs) using the model photosynthetic alga as a recipient.

Comparative analysis of plastocyanin-cytochrome f complex formation in higher plants, green algae and cyanobacteria.

Mechanisms of the complex formation between plastocyanin and cytochrome f in higher plants (Spinacia oleracea and Brassica rapa), green microalgae Chlamydomonas reinhardtii and two species of cyanobacteria (Phormidium laminosum and Nostoc sp.) were investigated using combined Brownian and molecular dynamics simulations and hierarchical cluster analysis. In higher plants and green algae, electrostatic interactions force plastocyanin molecule close to the heme of cytochrome f.

Comparative analyses of H photoproduction in magnesium- and sulfur-starved Chlamydomonas reinhardtii cultures.

Magnesium (Mg)-deprived Chlamydomonas reinhardtii cells are capable to sustain hydrogen (H ) photoproduction at relatively high photosystem II (PSII) activity levels for an extended time period as compared with sulfur (S)-deprived cells. Herein, we present a comparative study of H photoproduction induced by Mg and S shortage to unravel the specific rearrangements of the photosynthetic machinery and cell metabolism occurring under the two deprivation protocols. The exhaustive analysis of photosynthetic activity and regulatory pathways, respiration and starch metabolism revealed the specific rearrangements of the photosynthetic machinery and cellular metabolism, which occur under the two deprivation conditions.

Multiparticle Brownian dynamics simulation of experimental kinetics of cytochrome bf oxidation and photosystem I reduction by plastocyanin.

A model of electron transport from cytochrome f to photosystem I mediated by plastocyanin was designed on the basis of the multiparticle Brownian dynamics method. The model combines events which occur over a wide time range, including protein diffusion along the thylakoid membrane, long-distance interactions between proteins, formation of a multiprotein complex, electron transfer within a complex and complex dissociation. Results of the modeling were compared with the experimental kinetics measured in chloroplast thylakoids.

Potential of carbon nanotubes in algal biotechnology.

A critical mass of knowledge is emerging on the interactions between plant cells and engineered nanomaterials, revealing the potential of plant nanobiotechnology to promote and support novel solutions for the development of a competitive bioeconomy. This knowledge can foster the adoption of new methodological strategies to empower the large-scale production of biomass from commercially important microalgae. The present review focuses on the potential of carbon nanotubes (CNTs) to enhance photosynthetic performance of microalgae by (i) widening the spectral region available for the energy conversion reactions and (ii) increasing the tolerance of microalgae towards unfavourable conditions occurring in mass production.

Multiple regulatory mechanisms in the chloroplast of green algae: relation to hydrogen production.

A complex regulatory network in the chloroplast of green algae provides an efficient tool for maintenance of energy and redox balance in the cell under aerobic and anaerobic conditions. In this review, we discuss the structural and functional organizations of electron transport pathways in the chloroplast, and regulation of photosynthesis in the green microalga Chlamydomonas reinhardtii. The focus is on the regulatory mechanisms induced in response to nutrient deficiency stress and anoxia and especially on the role of a hydrogenase-mediated reaction in adaptation to highly reducing conditions and ATP deficiency in the cell.

Photosynthesis-related quantities for education and modeling.

A quantitative understanding of the photosynthetic machinery depends largely on quantities, such as concentrations, sizes, absorption wavelengths, redox potentials, and rate constants. The present contribution is a collection of numbers and quantities related mainly to photosynthesis in higher plants. All numbers are taken directly from a literature or database source and the corresponding reference is provided.

Antimycin A effect on the electron transport in chloroplasts of two Chlamydomonas reinhardtii strains.

The effects of antimycin A on the redox state of plastoquinone and on electron donation to photosystem I (PS I) were studied in sulfur-deprived Chlamydomonas reinhardtii cells of the strains cc406 and 137c. We found that this reagent suppresses cyclic electron flow around PS I in the cc406 strain, whereas this inhibitory effect was completely absent in the 137c strain. In the latter strain, antimycin A induced rapid reduction of plastoquinone in the dark and considerably enhanced the rate of electron donation to P700 (+) in the dark.

Membrane potential is involved in regulation of photosynthetic reactions in the marine diatom Thalassiosira weissflogii.

High-intensity Chl fluorescence transients (OJIP transients) and light-induced kinetics of the delayed light emission were measured in diatom microalga Thalassiosira weissflogii in the presence of various uncouplers and photosynthetic inhibitors. The I step in the OJIP transients in T. weissflogii was essentially reduced or completely absent but was restored in the presence of uncouplers valinomycin, FCCP, and nigericin.

Acclimation of green algae to sulfur deficiency: underlying mechanisms and application for hydrogen production.

Hydrogen is definitely one of the most acceptable fuels in the future. Some photosynthetic microorganisms, such as green algae and cyanobacteria, can produce hydrogen gas from water by using solar energy. In green algae, hydrogen evolution is coupled to the photosynthetic electron transport in thylakoid membranes via reaction catalyzed by the specific enzyme, (FeFe)-hydrogenase.

Two-electron reactions S2QB -->S0QB and S3QB -->S1QB are involved in deactivation of higher S states of the oxygen-evolving complex of Photosystem II.

The oxygen-evolving complex of Photosystem II cycles through five oxidation states (S(0)-S(4)), and dark incubation leads to 25% S(0) and 75% S(1). This distribution cannot be reached with charge recombination reactions between the higher S states and the electron acceptor Q(B)(-). We measured flash-induced oxygen evolution to understand how S(3) and S(2) are converted to lower S states when the electron required to reduce the manganese cluster does not come from Q(B)(-).

Illumination with ultraviolet or visible light induces chemical changes in the water-soluble manganese complex, [Mn(4)O(6)(bpea)(4)]Br(4).

We measured the photosensitivity of an artificial tetranuclear oxo-Mn(IV) complex, [Mn(4)O(6)(bpea)(4)]Br(4), which has an adamantane-shaped {Mn(4)O(6)}(4+) core. Illumination caused changes in the absorption spectrum of the compound consistent with a one-electron reduction in the compound. Bromide appears to be the most probable electron donor in the reaction system.

Hydrogen production by photoautotrophic sulfur-deprived Chlamydomonas reinhardtii pre-grown and incubated under high light.

We have previously demonstrated that Chlamydomonas reinhardtii can produce hydrogen under strictly photoautotrophic conditions during sulfur deprivation [Tsygankov et al. (2006); Int J Hydrogen Energy 3:1574-1584]. The maximum hydrogen photoproduction was achieved by photoautotrophic cultures pre-grown under a low light regime (25 microE m(-2) s(-1)).

Study of photosystem 2 heterogeneity in the sulfur-deficient green alga Chlamydomonas reinhardtii.

A set of chlorophyll fluorescence methods, including PEA (Plant Efficiency Analyser), PAM (Pulse Amplitude Modulated fluorometer), and picosecond fluorometer, was employed to study PS 2 heterogeneity in sulfur deprived green algae Chlamydomonas reinhardtii. The regression method and JIP test were applied to analyze chlorophyll fluorescence kinetics. The fractions of PS 2 characterized by the energetic disconnection, smaller antenna size, elevated constant rate of primary photochemistry, and inability to maintain DeltapH-dependent energy dissipation increased essentially already after 12 h of incubation in sulfur depleted medium.