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Annals of Botany Sep 2020With limited agricultural land and increasing human population, it is essential to enhance overall photosynthesis and thus productivity. Oxygenic photosynthesis begins... (Review)
Review
BACKGROUND
With limited agricultural land and increasing human population, it is essential to enhance overall photosynthesis and thus productivity. Oxygenic photosynthesis begins with light absorption, followed by excitation energy transfer to the reaction centres, primary photochemistry, electron and proton transport, NADPH and ATP synthesis, and then CO2 fixation (Calvin-Benson cycle, as well as Hatch-Slack cycle). Here we cover some of the discoveries related to this process, such as the existence of two light reactions and two photosystems connected by an electron transport 'chain' (the Z-scheme), chemiosmotic hypothesis for ATP synthesis, water oxidation clock for oxygen evolution, steps for carbon fixation, and finally the diverse mechanisms of regulatory processes, such as 'state transitions' and 'non-photochemical quenching' of the excited state of chlorophyll a.
SCOPE
In this review, we emphasize that mathematical modelling is a highly valuable tool in understanding and making predictions regarding photosynthesis. Different mathematical models have been used to examine current theories on diverse photosynthetic processes; these have been validated through simulation(s) of available experimental data, such as chlorophyll a fluorescence induction, measured with fluorometers using continuous (or modulated) exciting light, and absorbance changes at 820 nm (ΔA820) related to redox changes in P700, the reaction centre of photosystem I.
CONCLUSIONS
We highlight here the important role of modelling in deciphering and untangling complex photosynthesis processes taking place simultaneously, as well as in predicting possible ways to obtain higher biomass and productivity in plants, algae and cyanobacteria.
Topics: Biomass; Chlorophyll; Chlorophyll A; Electron Transport; Humans; Light; Oxygen; Photosynthesis; Photosystem II Protein Complex; Water
PubMed: 31641747
DOI: 10.1093/aob/mcz171 -
Annual Review of Biophysics May 2021Phycobilisomes (PBSs) are extremely large chromophore-protein complexes on the stromal side of the thylakoid membrane in cyanobacteria and red algae. The main function... (Review)
Review
Phycobilisomes (PBSs) are extremely large chromophore-protein complexes on the stromal side of the thylakoid membrane in cyanobacteria and red algae. The main function of PBSs is light harvesting, and they serve as antennas and transfer the absorbed energy to the reaction centers of two photosynthetic systems (photosystems I and II). PBSs are composed of phycobiliproteins and linker proteins. How phycobiliproteins and linkers are organized in PBSs and how light energy is efficiently harvested and transferred in PBSs are the fundamental questions in the study of photosynthesis. In this review, the structures of the red algae and are discussed in detail, along with the functions of linker proteins in phycobiliprotein assembly and in fine-tuning the energy state of chromophores.
Topics: Photosynthesis; Phycobilisomes; Rhodophyta
PubMed: 33957054
DOI: 10.1146/annurev-biophys-062920-063657 -
Chemistry (Weinheim An Der Bergstrasse,... Feb 2022Mimicking photosynthesis using artificial systems, as a means for solar energy conversion and green fuel generation, is one of the holy grails of modern science. This... (Review)
Review
Mimicking photosynthesis using artificial systems, as a means for solar energy conversion and green fuel generation, is one of the holy grails of modern science. This perspective presents recent advances towards developing artificial photosynthetic systems. In one approach, native photosystems are interfaced with electrodes to yield photobioelectrochemical cells that transform light energy into electrical power. This is exemplified by interfacing photosystem I (PSI) and photosystem II (PSII) as an electrically contacted assembly mimicking the native Z-scheme, and by the assembly of an electrically wired PSI/glucose oxidase biocatalytic conjugate on an electrode support. Illumination of the functionalized electrodes led to light-induced generation of electrical power, or to the generation of photocurrents using glucose as the fuel. The second approach introduces supramolecular photosensitizer nucleic acid/electron acceptor complexes as functional modules for effective photoinduced electron transfer stimulating the subsequent biocatalyzed generation of NADPH or the Pt-nanoparticle-catalyzed evolution of molecular hydrogen. Application of the DNA machineries for scaling-up the photosystems is demonstrated. A third approach presents the integration of artificial photosynthetic modules into dynamic nucleic acid networks undergoing reversible reconfiguration or dissipative transient operation in the presence of auxiliary triggers. Control over photoinduced electron transfer reactions and photosynthetic transformations by means of the dynamic networks is demonstrated.
Topics: Electron Transport; Photosynthesis; Photosystem I Protein Complex; Photosystem II Protein Complex; Solar Energy
PubMed: 34854505
DOI: 10.1002/chem.202103595 -
Anticancer Research Oct 2022Photosynthesis is the basis of almost all life on Earth. In addition to providing energy, plants and algae provide a plethora of secondary substances useful in the... (Review)
Review
Photosynthesis is the basis of almost all life on Earth. In addition to providing energy, plants and algae provide a plethora of secondary substances useful in the treatment of a number of illnesses including a wide array of cancer maladies. The first organisms on Earth used chemosynthesis for their energy needs. Photosynthetic bacteria utilize one of two different photosystems whereas cyanobacteria, eukaryotic algae and plants combine two photosystems in a linear electron transport chain. Accessory pigments such as various chlorophylls, carotenoids and phycobilins absorb the energy of impinging photons and funnel it to the reaction centers (P680 in photosystem II and P700 in photosystem I). Water is split photochemically, electrons are transported to reduce NADPH, oxygen is discarded as waste product, and protons accumulate inside the thylakoid vesicles in the chloroplasts. The resulting electrochemical gradient across the membrane is used to drive an ATPase. The produced ATP and NADPH+H are utilized in the Calvin cycle to fix CO and to produce fructose.
Topics: Adenosine Triphosphatases; Adenosine Triphosphate; Carbon Dioxide; Carotenoids; Electron Transport; Fructose; NADP; Oxygen; Photosynthesis; Photosystem I Protein Complex; Photosystem II Protein Complex; Phycobilins; Protons; Water
PubMed: 36191985
DOI: 10.21873/anticanres.16012 -
Annual Review of Plant Biology May 2023Photosystem II is the water-oxidizing and O-evolving enzyme of photosynthesis. How and when this remarkable enzyme arose are fundamental questions in the history of life... (Review)
Review
Photosystem II is the water-oxidizing and O-evolving enzyme of photosynthesis. How and when this remarkable enzyme arose are fundamental questions in the history of life that have remained difficult to answer. Here, recent advances in our understanding of the origin and evolution of photosystem II are reviewed and discussed in detail. The evolution of photosystem II indicates that water oxidation originated early in the history of life, long before the diversification of cyanobacteria and other major groups of prokaryotes, challenging and transforming current paradigms on the evolution of photosynthesis. We show that photosystem II has remained virtually unchanged for billions of years, and yet the nonstop duplication process of the D1 subunit of photosystem II, which controls photochemistry and catalysis, has enabled the enzyme to become adaptable to variable environmental conditions and even to innovate enzymatic functions beyond water oxidation. We suggest that this evolvability can be harnessed to develop novel light-powered enzymes with the capacity to carry out complex multistep oxidative transformations for sustainable biocatalysis.
Topics: Photosystem II Protein Complex; Photosynthesis; Water; Cyanobacteria; Oxidation-Reduction; Oxygen
PubMed: 36889003
DOI: 10.1146/annurev-arplant-070522-062509 -
FEBS Letters Jan 2023A computational methodology is briefly described, which appears to be able to accurately describe the mechanisms of redox active enzymes. The method is built on hybrid... (Review)
Review
A computational methodology is briefly described, which appears to be able to accurately describe the mechanisms of redox active enzymes. The method is built on hybrid density functional theory where the inclusion of a fraction of exact exchange is critical. Two examples of where the methodology has been applied are described. The first example is the mechanism for water oxidation in photosystem II, and the second one is the mechanism for N activation by nitrogenase. The mechanism for PSII has obtained very strong support from subsequent experiments. For nitrogenase, the calculations suggest that there should be an activation process prior to catalysis, which is still strongly debated.
Topics: Oxidation-Reduction; Nitrogenase; Computer Simulation; Photosystem II Protein Complex
PubMed: 36254111
DOI: 10.1002/1873-3468.14512 -
Plant & Cell Physiology Oct 2021Most of life's energy comes from sunlight, and thus, photosynthesis underpins the survival of virtually all life forms. The light-driven electron transfer at photosystem... (Review)
Review
Most of life's energy comes from sunlight, and thus, photosynthesis underpins the survival of virtually all life forms. The light-driven electron transfer at photosystem I (PSI) is certainly the most important generator of reducing power at the cellular level and thereby largely determines the global amount of enthalpy in living systems (Nelson 2011). The PSI is a light-driven plastocyanin:ferredoxin oxidoreductase, which is embedded into thylakoid membranes of cyanobacteria and chloroplasts of eukaryotic photosynthetic organism. Structural determination of complexes of the photosynthetic machinery is vital for the understanding of its mode of action. Here, we describe new structural and functional insights into PSI and associated light-harvesting proteins, with a focus on the plasticity of PSI.
Topics: Adaptation, Physiological; Cryoelectron Microscopy; Cytochrome b6f Complex; Photosystem I Protein Complex; Plants; Protein Structure, Tertiary
PubMed: 33768246
DOI: 10.1093/pcp/pcab046 -
Frontiers in Microbiology 2021Unraveling the oligomeric states of the photosystem I complex is essential to understanding the evolution and native mechanisms of photosynthesis. The molecular... (Review)
Review
Unraveling the oligomeric states of the photosystem I complex is essential to understanding the evolution and native mechanisms of photosynthesis. The molecular composition and functions of this complex are highly conserved among cyanobacteria, algae, and plants; however, its structure varies considerably between species. In cyanobacteria, the photosystem I complex is a trimer in most species, but monomer, dimer and tetramer arrangements with full physiological function have recently been characterized. Higher order oligomers have also been identified in some heterocyst-forming cyanobacteria and their close unicellular relatives. Given technological progress in cryo-electron microscope single particle technology, structures of PSI dimers, tetramers and some heterogeneous supercomplexes have been resolved into near atomic resolution. Recent developments in photosystem I oligomer studies have largely enriched theories on the structure and function of these photosystems.
PubMed: 35281305
DOI: 10.3389/fmicb.2021.781826 -
ELife Sep 2020Carotenoids are essential in oxygenic photosynthesis: they stabilize the pigment-protein complexes, are active in harvesting sunlight and in photoprotection. In plants,...
Carotenoids are essential in oxygenic photosynthesis: they stabilize the pigment-protein complexes, are active in harvesting sunlight and in photoprotection. In plants, they are present as carotenes and their oxygenated derivatives, xanthophylls. While mutant plants lacking xanthophylls are capable of photoautotrophic growth, no plants without carotenes in their photosystems have been reported so far, which has led to the common opinion that carotenes are essential for photosynthesis. Here, we report the first plant that grows photoautotrophically in the absence of carotenes: a tobacco plant containing only the xanthophyll astaxanthin. Surprisingly, both photosystems are fully functional despite their carotenoid-binding sites being occupied by astaxanthin instead of β-carotene or remaining empty (i.e. are not occupied by carotenoids). These plants display non-photochemical quenching, despite the absence of both zeaxanthin and lutein and show that tobacco can regulate the ratio between the two photosystems in a very large dynamic range to optimize electron transport.
Topics: Photosynthesis; Plants, Genetically Modified; Nicotiana; Xanthophylls; beta Carotene
PubMed: 32975516
DOI: 10.7554/eLife.58984 -
Photochemical & Photobiological... May 2020Photosynthetic organisms are exposed to a fluctuating environment in which light intensity and quality change continuously. Specific illumination of either photosystem... (Review)
Review
Photosynthetic organisms are exposed to a fluctuating environment in which light intensity and quality change continuously. Specific illumination of either photosystem (PSI or PSII) creates an energy imbalance, leading to the reduction or oxidation of the intersystem electron transport chain. This redox imbalance could trigger the formation of dangerous reactive oxygen species. Cyanobacteria, like plants and algae, have developed a mechanism to re-balance this preferential excitation of either reaction center, called state transitions. State transitions are triggered by changes in the redox state of the membrane-soluble plastoquinone (PQ) pool. In plants and green algae, these changes in redox potential are sensed by Cytochrome bf, which interacts with a specific kinase that triggers the movement of the main PSII antenna (the light-harvesting complex II). By contrast, although cyanobacterial state transitions have been studied extensively, there is still no agreement about the molecular mechanism, the PQ redox state sensor and the signaling pathways involved. In this review, we aimed to critically evaluate the results published on cyanobacterial state transitions, and discuss the "new" and "old" models in the subject. The phycobilisome and membrane contributions to this physiological process were addressed and the current hypotheses regarding its signaling transduction pathway were discussed.
Topics: Cyanobacteria; Oxidation-Reduction; Photosystem I Protein Complex; Photosystem II Protein Complex
PubMed: 32163064
DOI: 10.1039/c9pp00451c