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Milrad Y, Nagy V, Elman T, Fadeeva M, Tóth SZ, Yacoby I. A PSII photosynthetic control is activated in anoxic cultures of green algae following illumination. Commun Biol 2023; 6:514. [PMID: 37173420 PMCID: PMC10182038 DOI: 10.1038/s42003-023-04890-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Accepted: 05/01/2023] [Indexed: 05/15/2023] Open
Abstract
Photosynthetic hydrogen production from microalgae is considered to have potential as a renewable energy source. Yet, the process has two main limitations holding it back from scaling up; (i) electron loss to competing processes, mainly carbon fixation and (ii) sensitivity to O2 which diminishes the expression and the activity of the hydrogenase enzyme catalyzing H2 production. Here we report a third, hitherto unknown challenge: We found that under anoxia, a slow-down switch is activated in photosystem II (PSII), diminishing the maximal photosynthetic productivity by three-fold. Using purified PSII and applying in vivo spectroscopic and mass spectrometric techniques on Chlamydomonas reinhardtii cultures, we show that this switch is activated under anoxia, within 10 s of illumination. Furthermore, we show that the recovery to the initial rate takes place following 15 min of dark anoxia, and propose a mechanism in which, modulation in electron transfer at the acceptor site of PSII diminishes its output. Such insights into the mechanism broaden our understanding of anoxic photosynthesis and its regulation in green algae and inspire new strategies to improve bio-energy yields.
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Affiliation(s)
- Yuval Milrad
- School of Plant Sciences and Food Security, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv, 69978, Israel
| | - Valéria Nagy
- Institute of Plant Biology, Biological Research Centre, Szeged, Temesvári krt. 62, H-6726 Szeged, Hungary
| | - Tamar Elman
- School of Plant Sciences and Food Security, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv, 69978, Israel
| | - Maria Fadeeva
- Department of Biochemistry, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv, 69978, Israel
| | - Szilvia Z Tóth
- Institute of Plant Biology, Biological Research Centre, Szeged, Temesvári krt. 62, H-6726 Szeged, Hungary
| | - Iftach Yacoby
- School of Plant Sciences and Food Security, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv, 69978, Israel.
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Gates C, Ananyev G, Roy-Chowdhury S, Fromme P, Dismukes GC. Regulation of light energy conversion between linear and cyclic electron flow within photosystem II controlled by the plastoquinone/quinol redox poise. PHOTOSYNTHESIS RESEARCH 2023; 156:113-128. [PMID: 36436152 DOI: 10.1007/s11120-022-00985-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Accepted: 11/09/2022] [Indexed: 06/16/2023]
Abstract
Ultrapurified Photosystem II complexes crystalize as uniform microcrystals (PSIIX) of unprecedented homogeneity that allow observation of details previously unachievable, including the longest sustained oscillations of flash-induced O2 yield over > 200 flashes and a novel period-4.7 water oxidation cycle. We provide new evidence for a molecular-based mechanism for PSII-cyclic electron flow that accounts for switching from linear to cyclic electron flow within PSII as the downstream PQ/PQH2 pool reduces in response to metabolic needs and environmental input. The model is supported by flash oximetry of PSIIX as the LEF/CEF switch occurs, Fourier analysis of O2 flash yields, and Joliot-Kok modeling. The LEF/CEF switch rebalances the ratio of reductant energy (PQH2) to proton gradient energy (H+o/H+i) created by PSII photochemistry. Central to this model is the requirement for a regulatory site (QC) with two redox states in equilibrium with the dissociable secondary electron carrier site QB. Both sites are controlled by electrons and protons. Our evidence fits historical LEF models wherein light-driven water oxidation delivers electrons (from QA-) and stromal protons through QB to generate plastoquinol, the terminal product of PSII-LEF in vivo. The new insight is the essential regulatory role of QC. This site senses both the proton gradient (H+o/H+i) and the PQ pool redox poise via e-/H+ equilibration with QB. This information directs switching to CEF upon population of the protonated semiquinone in the Qc site (Q-H+)C, while the WOC is in the reducible S2 or S3 states. Subsequent photochemical primary charge separation (P+QA-) forms no (QH2)B, but instead undergoes two-electron backward transition in which the QC protons are pumped into the lumen, while the electrons return to the WOC forming (S1/S2). PSII-CEF enables production of additional ATP needed to power cellular processes including the terminal carboxylation reaction and in some cases PSI-dependent CEF.
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Affiliation(s)
- Colin Gates
- Dept of Chemistry & Chemical Biology, Rutgers University, Piscataway, USA
- Waksman Institute of Microbiology, Rutgers University, Piscataway, USA
- Dept of Computational Biology & Molecular Biophysics, Rutgers University, Piscataway, NJ, USA
- Dept of Chemistry and Biochemistry, Loyola University Chicago, Chicago, IL, USA
| | - Gennady Ananyev
- Dept of Chemistry & Chemical Biology, Rutgers University, Piscataway, USA
- Waksman Institute of Microbiology, Rutgers University, Piscataway, USA
| | - Shatabdi Roy-Chowdhury
- Center for Applied Structural Discovery, Biodesign Institute, Arizona State University, Tempe, AZ, USA
| | - Petra Fromme
- Center for Applied Structural Discovery, Biodesign Institute, Arizona State University, Tempe, AZ, USA
| | - G Charles Dismukes
- Dept of Chemistry & Chemical Biology, Rutgers University, Piscataway, USA.
- Waksman Institute of Microbiology, Rutgers University, Piscataway, USA.
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Zournas A, Mani K, Dismukes GC. Cyclic electron flow around photosystem II in silico: How it works and functions in vivo. PHOTOSYNTHESIS RESEARCH 2023; 156:129-145. [PMID: 36753032 DOI: 10.1007/s11120-023-00997-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2022] [Accepted: 12/29/2022] [Indexed: 06/18/2023]
Abstract
To date, cyclic electron flow around PSI (PSI-CEF) has been considered the primary (if not the only) mechanism accepted to adjust the ratio of linear vs cyclic electron flow that is essential to adjust the ratio of ATP/NADPH production needed for CO2 carboxylation. Here we provide a kinetic model showing that cyclic electron flow within PSII (PSII-CEF) is essential to account for the accelerating rate of decay in flash-induced oscillations of O2 yield as the PQ pool progressively reduces to PQH2. Previously, PSII-CEF was modeled by backward transitions using empirical Markov models like Joliot-Kok (J-K) type. Here, we adapted an ordinary differential equation methodology denoted RODE1 to identify which microstates within PSII are responsible for branching between PSII-CEF and Linear Electron Flow (LEF). We applied it to simulate the oscillations of O2 yield from both Chlorella ohadii, an alga that shows strong PSII-CEF attributed to high backward transitions, and Synechococcus elongatus sp. 7002, a widely studied model cyanobacterium. RODE2 simulations reveal that backward transitions occur in microstates that possess a QB- semiquinone prior to the flash. Following a flash that forms microstates populating (QAQB)2-, PSII-CEF redirects these two electrons to the donor side of PSII only when in the oxidized S2 and S3 states. We show that this backward transition pathway is the origin of the observed period-2 oscillations of flash O2 yield and contributes to the accelerated decay of period-4 oscillations. This newly added pathway improved RODE1 fits for cells of both S. elongatus and C. ohadii. RODE2 simulations show that cellular adaptation to high light intensity growth is due to a decrease in QB availability (empty or blocked by Q2-B), or equivalently due to a decrease in the difference in reduction potential relative to QA/QA-. PSII-CEF provides an alternative mechanism for rebalancing the NADPH:ATP ratio that occurs rapidly by adjusting the redox level of the PQ:PQH2 pool and is a necessary process for energy metabolism in aquatic phototrophs.
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Affiliation(s)
- Apostolos Zournas
- Waksman Institute of Microbiology, Rutgers University, Piscataway, NJ, 08854, USA
- Department of Chemical and Biological Engineering, Rutgers University, Piscataway, NJ, 08854, USA
| | - Kyle Mani
- Waksman Institute of Microbiology, Rutgers University, Piscataway, NJ, 08854, USA
| | - G Charles Dismukes
- Waksman Institute of Microbiology, Rutgers University, Piscataway, NJ, 08854, USA.
- Department. of Chemistry & Chemical Biology, Rutgers University, Piscataway, NJ, 08854, USA.
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Lysenko V, D. Rajput V, Kumar Singh R, Guo Y, Kosolapov A, Usova E, Varduny T, Chalenko E, Yadronova O, Dmitriev P, Zaruba T. Chlorophyll fluorometry in evaluating photosynthetic performance: key limitations, possibilities, perspectives and alternatives. PHYSIOLOGY AND MOLECULAR BIOLOGY OF PLANTS : AN INTERNATIONAL JOURNAL OF FUNCTIONAL PLANT BIOLOGY 2022; 28:2041-2056. [PMID: 36573148 PMCID: PMC9789293 DOI: 10.1007/s12298-022-01263-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Revised: 10/25/2022] [Accepted: 12/06/2022] [Indexed: 06/17/2023]
Abstract
Non-destructive methods for the assessment of photosynthetic parameters of plants are widely applied to evaluate rapidly the photosynthetic performance, plant health, and shifts in plant productivity induced by environmental and cultivation conditions. Most of these methods are based on measurements of chlorophyll fluorescence kinetics, particularly on pulse modulation (PAM) fluorometry. In this paper, fluorescence methods are critically discussed in regard to some their possibilities and limitations inherent to vascular plants and microalgae. Attention is paid to the potential errors related to the underestimation of thylakoidal cyclic electron transport and anoxygenic photosynthesis. PAM-methods are also observed considering the color-addressed measurements. Photoacoustic methods are discussed as an alternative and supplement to fluorometry. Novel Fourier modifications of PAM-fluorometry and photoacoustics are noted as tools allowing simultaneous application of a dual or multi frequency measuring light for one sample.
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Affiliation(s)
- Vladimir Lysenko
- Academy of Biology and Biotechnology, Southern Federal University, Rostov-on-Don, Russia
| | - Vishnu D. Rajput
- Academy of Biology and Biotechnology, Southern Federal University, Rostov-on-Don, Russia
| | - Rupesh Kumar Singh
- Centre of Molecular and Environmental Biology, Department of Biology, Campus of Gualtar, University of Minho, Braga, Portugal
| | - Ya Guo
- School of IoT Engineering, Jiangnan University, Wuxi, China
| | - Alexey Kosolapov
- Russian Research Institute for the Integrated Use and Protection of Water Resources, Rostov-on-Don, Russia
| | - Elena Usova
- Russian Research Institute for the Integrated Use and Protection of Water Resources, Rostov-on-Don, Russia
| | - Tatyana Varduny
- Academy of Biology and Biotechnology, Southern Federal University, Rostov-on-Don, Russia
| | - Elizaveta Chalenko
- Academy of Biology and Biotechnology, Southern Federal University, Rostov-on-Don, Russia
| | - Olga Yadronova
- Academy of Biology and Biotechnology, Southern Federal University, Rostov-on-Don, Russia
| | - Pavel Dmitriev
- Academy of Biology and Biotechnology, Southern Federal University, Rostov-on-Don, Russia
| | - Tatyana Zaruba
- Academy of Biology and Biotechnology, Southern Federal University, Rostov-on-Don, Russia
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Lacour T, Larivière J, Ferland J, Morin PI, Grondin PL, Donaher N, Cockshutt A, Campbell DA, Babin M. Photoacclimation of the polar diatom Chaetoceros neogracilis at low temperature. PLoS One 2022; 17:e0272822. [PMID: 36125987 PMCID: PMC9488821 DOI: 10.1371/journal.pone.0272822] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Accepted: 07/26/2022] [Indexed: 11/18/2022] Open
Abstract
Polar microalgae face two major challenges: 1- growing at temperatures (-1.7 to 5°C) that limit enzyme kinetics; and 2- surviving and exploiting a wide range of irradiance. The objective of this study is to understand the adaptation of an Arctic diatom to its environment by studying its ability to acclimate to changes in light and temperature. We acclimated the polar diatom Chaetoceros neogracilis to various light levels at two different temperatures and studied its growth and photosynthetic properties using semi-continuous cultures. Rubisco content was high, to compensate for low catalytic rates, but did not change detectably with growth temperature. Contrary to what is observed in temperate species, in C. neogracilis, carbon fixation rate (20 min 14C incorporation) equaled net growth rate (μ) suggesting very low or very rapid (<20 min) re-oxidation of the newly fixed carbon. The comparison of saturation irradiances for electron transport, oxygen net production and carbon fixation revealed alternative electron pathways that could provide energy and reducing power to the cell without consuming organic carbon which is a very limiting product at low temperatures. High protein contents, low re-oxidation of newly fixed carbon and the use of electron pathways alternative to carbon fixation may be important characteristics allowing efficient growth under those extreme environmental conditions.
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Affiliation(s)
- Thomas Lacour
- Ifremer, PHYTOX, PHYSALG, Brest, France
- Département de Biologie, Takuvik International Research Laboratory (IRL-3376, CNRS (France) & ULaval (Canada), Université Laval, Québec, Canada
- * E-mail:
| | - Jade Larivière
- Département de Biologie, Takuvik International Research Laboratory (IRL-3376, CNRS (France) & ULaval (Canada), Université Laval, Québec, Canada
| | - Joannie Ferland
- Département de Biologie, Takuvik International Research Laboratory (IRL-3376, CNRS (France) & ULaval (Canada), Université Laval, Québec, Canada
| | - Philippe-Israël Morin
- Département de Biologie, Takuvik International Research Laboratory (IRL-3376, CNRS (France) & ULaval (Canada), Université Laval, Québec, Canada
| | - Pierre-Luc Grondin
- Département de Biologie, Takuvik International Research Laboratory (IRL-3376, CNRS (France) & ULaval (Canada), Université Laval, Québec, Canada
| | - Natalie Donaher
- Department of Chemistry and Biochemistry, Mount Allison University, Sackville, Canada
| | - Amanda Cockshutt
- Department of Chemistry and Biochemistry, Mount Allison University, Sackville, Canada
| | - Douglas A. Campbell
- Department of Chemistry and Biochemistry, Mount Allison University, Sackville, Canada
| | - Marcel Babin
- Département de Biologie, Takuvik International Research Laboratory (IRL-3376, CNRS (France) & ULaval (Canada), Université Laval, Québec, Canada
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González-Guerrero LA, Vásquez-Elizondo RM, López-Londoño T, Hernán G, Iglesias-Prieto R, Enríquez S. Validation of parameters and protocols derived from chlorophyll a fluorescence commonly utilised in marine ecophysiological studies. FUNCTIONAL PLANT BIOLOGY : FPB 2022; 49:517-532. [PMID: 34372966 DOI: 10.1071/fp21101] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2021] [Accepted: 07/08/2021] [Indexed: 06/13/2023]
Abstract
This study documents the first validation of the suitability of the most common parameters and protocols used in marine ecophysiology to characterise photosynthesis by means of chlorophyll a fluorescence tools. We demonstrate that the effective yield of PSII (ΔF /F m ') is significantly underestimated when using short inductions times (≤1 min) following the rapid light curve protocol (RLC). The consequent electron transport rates (ETR) underestimations are species-specific and highly variable with irradiance and the photoacclimatory condition of the sample. Our analysis also questions the use of relative descriptors (relETR), as they not only overestimate photosynthesis, but overlook one of the fundamental components of the photosynthetic response: light absorption regulation. Absorptance determinations were fundamental to characterise the ETR response of low-pigmented seagrass leaves, and also uncovered relevant differences between two coral species and the accclimatory response of a cultured dinoflagellate to temperature. ETR and oxygen evolution determinations showed close correlations for all organisms tested with the expected slope of 4 e- per O2 molecule evolved, when correct photosynthesis inductions and light absorption determinations were applied. However, ETR curves cannot be equated to conventional photosynthetic response to irradiance (P vs E ) curves, and caution is needed when using ETR to characterise photosynthesis rates above photosynthesis saturation (E k ). This validation strongly supports the utility of fluorescence tools, underlining the need to correct two decades of propagation of erroneous concepts, protocols and parameters in marine eco-physiology. We aim also to emphasise the importance of optical descriptions for understanding photosynthesis, and for interpreting fluorescence measurements. In combination with conventional gross photosynthesis (GPS) approaches, optical characterisations open an extraordinary opportunity to determine two central parameters of photosynthesis performance: the quantum yield (φmax ) of the process and its minimum quantum requirements (1/φmax ). The combination of both approaches potentiates the possibilities of chlorophyll a fluorescence tools to characterise marine photosynthesis biodiversity.
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Affiliation(s)
| | - Román M Vásquez-Elizondo
- Laboratory of Photobiology of coral reef primary producers, Unidad Académica de Sistemas Arrecifales Puerto Morelos, Universidad Nacional Autónoma de México (UNAM), Apartado Postal 13, 77500 Cancún, Mexico; and Present address: Laboratorio de Ficología Aplicada, Departamento de Recursos del Mar, CINVESTAV, Mérida
| | | | - Gema Hernán
- Laboratory of Photobiology of coral reef primary producers, Unidad Académica de Sistemas Arrecifales Puerto Morelos, Universidad Nacional Autónoma de México (UNAM), Apartado Postal 13, 77500 Cancún, Mexico
| | | | - Susana Enríquez
- Laboratory of Photobiology of coral reef primary producers, Unidad Académica de Sistemas Arrecifales Puerto Morelos, Universidad Nacional Autónoma de México (UNAM), Apartado Postal 13, 77500 Cancún, Mexico; and Corresponding author
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Lysenko V, Varduny T. High levels of anoxygenic photosynthesis revealed by dual-frequency Fourier photoacoustics in Ailanthus altissima leaves. FUNCTIONAL PLANT BIOLOGY : FPB 2022; 49:573-586. [PMID: 35413232 DOI: 10.1071/fp21093] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Accepted: 03/02/2022] [Indexed: 06/14/2023]
Abstract
In contrast to oxygenic photosynthesis, true anoxygenic photosynthesis is not associated with O2 evolution originated from water photolysis but still converts light energy to that of the phosphoanhydride bonds of ATP. In a narrow sense, anoxygenic photosynthesis is mainly known as to be related to the purple and green sulfur bacteria, but in a broad sense, it also occurs in the vascular plants. The portion of photosynthetic water photolysis that is compensated by the processes of O2 uptake (respiration, photorespiration, Mehler cycle, etc.) may be referred to as 'quasi' anoxygenic photosynthesis. Photoacoustic method allows for the separate detection of photolytic O2 at frequencies of measuring light about 20-40Hz, whereas at 250-400Hz, it detects the photochemical energy storage. We have developed a fast-Fourier transform photoacoustic method enabling measurements of both these signals simultaneously in one sample. This method allows to calculate oxygenic coefficients, which reflect the part of photochemically stored light energy that is used for the water photolysis. We show that the true anoxygenic photosynthesis in Ailanthus altissima Mill. leaves reached very high levels under low light, under moderate light at the beginning of the 1-h period, and at the end of the 40-min period under saturating light.
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Affiliation(s)
- Vladimir Lysenko
- Academy of Biology and Biotechnology, Southern Federal University, Botanichesky spusk 7, 344041 Rostov-on-Don, Russia
| | - Tatyana Varduny
- Academy of Biology and Biotechnology, Southern Federal University, Botanichesky spusk 7, 344041 Rostov-on-Don, Russia
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Camoying MG, Thoms S, Geuer JK, Koch BP, Bischof K, Trimborn S. In contrast to diatoms, cryptophytes are susceptible to iron limitation, but not to ocean acidification. PHYSIOLOGIA PLANTARUM 2022; 174:e13614. [PMID: 35199361 DOI: 10.1111/ppl.13614] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Revised: 12/09/2021] [Accepted: 12/17/2021] [Indexed: 06/14/2023]
Abstract
Previous field studies in the Southern Ocean (SO) indicated an increased occurrence and dominance of cryptophytes over diatoms due to climate change. To gain a better mechanistic understanding of how the two ecologically important SO phytoplankton groups cope with ocean acidification (OA) and iron (Fe) availability, we chose two common representatives of Antarctic waters, the cryptophyte Geminigera cryophila and the diatom Pseudo-nitzschia subcurvata. Both species were grown at 2°C under different pCO2 (400 vs. 900 μatm) and Fe (0.6 vs. 1.2 nM) conditions. For P. subcurvata, an additional high pCO2 level was applied (1400 μatm). At ambient pCO2 under low Fe supply, growth of G. cryophila almost stopped while it remained unaffected in P. subcurvata. Under high Fe conditions, OA was not beneficial for P. subcurvata, but stimulated growth and carbon production of G. cryophila. Under low Fe supply, P. subcurvata coped much better with OA than the cryptophyte, but invested more energy into photoacclimation. Our study reveals that Fe limitation was detrimental for the growth of G. cryophila and suppressed the positive OA effect. The diatom was efficient in coping with low Fe, but was stressed by OA while both factors together strongly impacted its growth. The distinct physiological response of both species to OA and Fe limitation explains their occurrence in the field. Based on our results, Fe availability is an important modulator of OA effects on SO phytoplankton, with different implications on the occurrence of cryptophytes and diatoms in the future.
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Affiliation(s)
- Marianne G Camoying
- Ecological Chemistry, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
| | - Silke Thoms
- Ecological Chemistry, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
| | - Jana K Geuer
- Ecological Chemistry, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
| | - Boris P Koch
- Ecological Chemistry, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
- Department of Technology, University of Applied Sciences Bremerhaven, Bremerhaven, Germany
| | - Kai Bischof
- Marine Botany & MARUM, University of Bremen, Bremen, Germany
| | - Scarlett Trimborn
- Ecological Chemistry, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
- Marine Botany & MARUM, University of Bremen, Bremen, Germany
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Mani K, Zournas A, Dismukes GC. Bridging the gap between Kok-type and kinetic models of photosynthetic electron transport within Photosystem II. PHOTOSYNTHESIS RESEARCH 2022; 151:83-102. [PMID: 34402027 DOI: 10.1007/s11120-021-00868-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2021] [Accepted: 07/23/2021] [Indexed: 06/13/2023]
Abstract
Historically, two modeling approaches have been developed independently to describe photosynthetic electron transport (PET) from water to plastoquinone within Photosystem II (PSII): Markov models account for losses from finite redox transition probabilities but predict no reaction kinetics, and ordinary differential equation (ODE) models account for kinetics but not for redox inefficiencies. We have developed an ODE mathematical framework to calculate Markov inefficiencies of transition probabilities as defined in Joliot-Kok-type catalytic cycles. We adapted a previously published ODE model for PET within PSII that accounts for 238 individual steps to enable calculation of the four photochemical inefficiency parameters (miss, double hit, inactivation, backward transition) and the four redox accumulation states (S-states) that are predicted by the most advanced of the Joliot-Kok-type models (VZAD). Using only reaction kinetic parameters without other assumptions, the RODE-calculated time-averaged (e.g., equilibrium) inefficiency parameters and equilibrium S-state populations agree with those calculated by time-independent Joliot-Kok models. RODE also predicts their time-dependent values during transient photochemical steps for all 96 microstates involving PSII redox cofactors. We illustrate applications to two cyanobacteria, Arthrospira maxima and Synechococcus sp. 7002, where experimental data exists for the inefficiency parameters and the S-state populations, and historical data for plant chloroplasts as benchmarks. Significant findings: RODE predicts the microstates responsible for period-4 and period-2 oscillations of O2 and fluorescence yields and the four inefficiency parameters; the latter parameters are not constant for each S state nor in time, in contrast to predictions from Joliot-Kok models; some of the recombination pathways that contribute to the backward transition parameter are identified and found to contribute when their rates exceed the oxidation rate of the terminal acceptor pool (PQH2); prior reports based on the assumptions of Joliot-Kok parameters may require reinterpretation.
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Affiliation(s)
- Kyle Mani
- Waksman Institute of Microbiology, Rutgers University, Piscataway, NJ, 08854, USA
- Department of Biomedical Engineering, Rutgers University, Piscataway, NJ, 08854, USA
| | - Apostolos Zournas
- Waksman Institute of Microbiology, Rutgers University, Piscataway, NJ, 08854, USA
- Department of Chemical and Biochemical Engineering, Rutgers University, Piscataway, NJ, 08854, USA
| | - G Charles Dismukes
- Waksman Institute of Microbiology, Rutgers University, Piscataway, NJ, 08854, USA.
- Department of Chemistry & Chemical Biology, Rutgers University, Piscataway, NJ, 08854, USA.
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Pagnone A, Koch F, Pausch F, Trimborn S. The Southern Ocean diatom Pseudo-nitzschia subcurvata flourished better under simulated glacial than interglacial ocean conditions: Combined effects of CO2 and iron. PLoS One 2021; 16:e0260649. [PMID: 34890411 PMCID: PMC8664213 DOI: 10.1371/journal.pone.0260649] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2021] [Accepted: 11/12/2021] [Indexed: 11/19/2022] Open
Abstract
The 'Iron Hypothesis' suggests a fertilization of the Southern Ocean by increased dust deposition in glacial times. This promoted high primary productivity and contributed to lower atmospheric pCO2. In this study, the diatom Pseudo-nitzschia subcurvata, known to form prominent blooms in the Southern Ocean, was grown under simulated glacial and interglacial climatic conditions to understand how iron (Fe) availability (no Fe or Fe addition) in conjunction with different pCO2 levels (190 and 290 μatm) influences growth, particulate organic carbon (POC) production and photophysiology. Under both glacial and interglacial conditions, the diatom grew with similar rates. In comparison, glacial conditions (190 μatm pCO2 and Fe input) favored POC production by P. subcurvata while under interglacial conditions (290 μatm pCO2 and Fe deficiency) POC production was reduced, indicating a negative effect caused by higher pCO2 and low Fe availability. Under interglacial conditions, the diatom had, however, thicker silica shells. Overall, our results show that the combination of higher Fe availability with low pCO2, present during the glacial ocean, was beneficial for the diatom P. subcurvata, thus contributing more to primary production during glacial compared to interglacial times. Under the interglacial ocean conditions, on the other hand, the diatom could have contributed to higher carbon export due to its higher degree of silicification.
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Affiliation(s)
- Anna Pagnone
- EcoTrace, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
| | - Florian Koch
- EcoTrace, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
| | - Franziska Pausch
- EcoTrace, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
| | - Scarlett Trimborn
- EcoTrace, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
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Yu W, Zhang L, Zhao J, Liu J. Exogenous sodium fumarate enhances astaxanthin accumulation in Haematococcus pluvialis by enhancing the respiratory metabolic pathway. BIORESOURCE TECHNOLOGY 2021; 341:125788. [PMID: 34461402 DOI: 10.1016/j.biortech.2021.125788] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 08/11/2021] [Accepted: 08/12/2021] [Indexed: 06/13/2023]
Abstract
Improvement of astaxanthin yield is a continuing objective in Haematococcus pluvialis cultivation. In this study, a new strategy combining exogenous sodium fumarate (SF) with nitrogen deficiency was demonstrated to promote astaxanthin accumulation in H. pluvialis. SF significantly accelerated astaxanthin synthesis over cell growth. Notably, under nitrogen deficiency, 10 mM SF increased the cellular astaxanthin content by 1.75-fold and 1.47-fold on day 7 and 12, respectively. Further studies indicated that SF increased the level of respiratory metabolites in the Embden-Meyerhof-Parnas pathway, tricarboxylic acid cycle and pentose phosphate pathway. An enhanced substrate pool due to the acceleration of respiratory metabolic pathways directly induced astaxanthin synthesis. Meanwhile, the accumulation of C18:1, C18:2 and C18:3 fatty acids enhanced astaxanthin synthesis indirectly by promoting the process of esterification. This study not only helps to elucidate the role of respiratory metabolic pathways in astaxanthin synthesis but also provides a new effective technique to improve astaxanthin production.
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Affiliation(s)
- Wenjie Yu
- Key Laboratory of Experimental Marine Biology, Center for Ocean Mega-Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Litao Zhang
- Key Laboratory of Experimental Marine Biology, Center for Ocean Mega-Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China
| | - Jing Zhao
- Key Laboratory of Experimental Marine Biology, Center for Ocean Mega-Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China; School of Marine Science and Engineering, Qingdao Agricultural University, Qingdao 266109, China
| | - Jianguo Liu
- Key Laboratory of Experimental Marine Biology, Center for Ocean Mega-Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China.
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12
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Bonnanfant M, Marec H, Jesus B, Mouget JL, Pruvost J. Investigation of the photosynthetic response of Chlorella vulgaris to light changes in a torus-shape photobioreactor. Appl Microbiol Biotechnol 2021; 105:8689-8701. [PMID: 34724082 DOI: 10.1007/s00253-021-11636-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2021] [Revised: 09/14/2021] [Accepted: 10/05/2021] [Indexed: 10/20/2022]
Abstract
An efficient use of light is essential to achieve good performances in microalgae cultivation systems. This can be challenging particularly under solar conditions where light is highly dynamic (e.g., day/night cycles, rapid changes in wind and weather conditions). Microalgae display different mechanisms to optimize light use efficiency. In the short term, when high light is encountered, several processes of photoprotection can be involved to avoid cell damages (e.g., xanthophyll cycle). In the long term, when cells are exposed to a different light intensity, pigment content changes, i.e., photoacclimation. The purpose of this study is to investigate the photosynthetic response of Chlorella vulgaris cultures grown in closed lab-scale, torus-shape photobioreactor under well-controlled light conditions, namely, constant and dynamic light transitions. Experiments were conducted in continuous mode with detailed characterization of the light attenuation conditions for each condition, as represented by the mean rate of photon absorption (MRPA), so as to characterize the time responses of the photosynthetic cells toward light changes. This enables to observe short-term and long-term responses with their own characteristic times. The mechanisms involved were found to be different between increasing and decreasing light transitions. Furthermore the MRPA was found a valuable parameter to relate the effect of light to biological responses (i.e., pigment changes) under constant light and dynamic light conditions.Key points• MRPA proved valuable to relate C. vulgaris responses to light changes.• A linear evolution was found between pigment content and MRPA in continuous light.• A rising PFD step induced fast protection and acclimation mechanisms.
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Affiliation(s)
- M Bonnanfant
- GEPEA, UMR 6144, Oniris, CNRS, Université de Nantes, 44600, Saint-Nazaire, France.,Mer-Molécules-Santé (MMS), EA 2160, Le Mans Université, Le Mans Cedex 9, France
| | - H Marec
- GEPEA, UMR 6144, Oniris, CNRS, Université de Nantes, 44600, Saint-Nazaire, France
| | - B Jesus
- Mer-Molécules-Santé (MMS), EA2160, Faculté Des Sciences, Université de Nantes, Nantes, France
| | - J-L Mouget
- Mer-Molécules-Santé (MMS), EA 2160, Le Mans Université, Le Mans Cedex 9, France
| | - J Pruvost
- GEPEA, UMR 6144, Oniris, CNRS, Université de Nantes, 44600, Saint-Nazaire, France.
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13
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Bhagooli R, Mattan-Moorgawa S, Kaullysing D, Louis YD, Gopeechund A, Ramah S, Soondur M, Pilly SS, Beesoo R, Wijayanti DP, Bachok ZB, Monrás VC, Casareto BE, Suzuki Y, Baker AC. Chlorophyll fluorescence - A tool to assess photosynthetic performance and stress photophysiology in symbiotic marine invertebrates and seaplants. MARINE POLLUTION BULLETIN 2021; 165:112059. [PMID: 33677415 DOI: 10.1016/j.marpolbul.2021.112059] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/25/2019] [Revised: 12/30/2020] [Accepted: 01/01/2021] [Indexed: 06/12/2023]
Abstract
Chlorophyll a fluorescence is increasingly being used as a rapid, non-invasive, sensitive and convenient indicator of photosynthetic performance in marine autotrophs. This review presents the methodology, applications and limitations of chlorophyll fluorescence in marine studies. The various chlorophyll fluorescence tools such as Pulse-Amplitude-Modulated (PAM) and Fast Repetition Rate (FRR) fluorometry used in marine scientific studies are discussed. Various commonly employed chlorophyll fluorescence parameters are elaborated. The application of chlorophyll fluorescence in measuring natural variations, stress, stress tolerance and acclimation/adaptation to changing environment in primary producers such as microalgae, macroalgae, seagrasses and mangroves, and marine symbiotic invertebrates, namely symbiotic sponges, hard corals and sea anemones, kleptoplastic sea slugs and giant clams is critically assessed. Stressors include environmental, biological, physical and chemical ones. The strengths, limitations and future perspectives of the use of chlorophyll fluorescence technique as an assessment tool in symbiotic marine organisms and seaplants are discussed.
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Affiliation(s)
- Ranjeet Bhagooli
- Department of Biosciences & Ocean Studies, Faculty of Science & Pole of Research Excellence, Sustainable Marine Biodiversity Research Group, University of Mauritius, Réduit 80837, Mauritius; The Biodiversity and Environment Institute, Réduit, Mauritius; The Society of Biology (Mauritius), Réduit, Mauritius; Institute of Oceanography and Environment (INOS), Universiti Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, Malaysia.
| | - Sushma Mattan-Moorgawa
- Department of Biosciences & Ocean Studies, Faculty of Science & Pole of Research Excellence, Sustainable Marine Biodiversity Research Group, University of Mauritius, Réduit 80837, Mauritius; The Biodiversity and Environment Institute, Réduit, Mauritius
| | - Deepeeka Kaullysing
- Department of Biosciences & Ocean Studies, Faculty of Science & Pole of Research Excellence, Sustainable Marine Biodiversity Research Group, University of Mauritius, Réduit 80837, Mauritius; The Biodiversity and Environment Institute, Réduit, Mauritius
| | - Yohan Didier Louis
- Department of Biosciences & Ocean Studies, Faculty of Science & Pole of Research Excellence, Sustainable Marine Biodiversity Research Group, University of Mauritius, Réduit 80837, Mauritius
| | - Arvind Gopeechund
- Department of Biosciences & Ocean Studies, Faculty of Science & Pole of Research Excellence, Sustainable Marine Biodiversity Research Group, University of Mauritius, Réduit 80837, Mauritius; The Biodiversity and Environment Institute, Réduit, Mauritius
| | - Sundy Ramah
- Department of Biosciences & Ocean Studies, Faculty of Science & Pole of Research Excellence, Sustainable Marine Biodiversity Research Group, University of Mauritius, Réduit 80837, Mauritius
| | - Mouneshwar Soondur
- Department of Biosciences & Ocean Studies, Faculty of Science & Pole of Research Excellence, Sustainable Marine Biodiversity Research Group, University of Mauritius, Réduit 80837, Mauritius; The Biodiversity and Environment Institute, Réduit, Mauritius
| | - Sivajyodee Sannassy Pilly
- Department of Biosciences & Ocean Studies, Faculty of Science & Pole of Research Excellence, Sustainable Marine Biodiversity Research Group, University of Mauritius, Réduit 80837, Mauritius
| | - Rima Beesoo
- Department of Biosciences & Ocean Studies, Faculty of Science & Pole of Research Excellence, Sustainable Marine Biodiversity Research Group, University of Mauritius, Réduit 80837, Mauritius
| | | | - Zainudin Bin Bachok
- Institute of Oceanography and Environment (INOS), Universiti Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, Malaysia
| | - Víctor Cubillos Monrás
- Instituto de Ciencias Marinas y Limnológicas, Laboratorio Costero de Recursos Acuáticos de Calfuco, Universidad Austral de Chile, Valdivia, Chile
| | | | - Yoshimi Suzuki
- Shizuoka University, 836 Oya, Suruga, Shizuoka, Shizuoka, Japan
| | - Andrew Charles Baker
- Department of Marine Biology and Ecology, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA
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14
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Raven JA, Beardall J, Quigg A. Light-Driven Oxygen Consumption in the Water-Water Cycles and Photorespiration, and Light Stimulated Mitochondrial Respiration. PHOTOSYNTHESIS IN ALGAE: BIOCHEMICAL AND PHYSIOLOGICAL MECHANISMS 2020. [DOI: 10.1007/978-3-030-33397-3_8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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15
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Bonnanfant M, Jesus B, Pruvost J, Mouget JL, Campbell DA. Photosynthetic electron transport transients in Chlorella vulgaris under fluctuating light. ALGAL RES 2019. [DOI: 10.1016/j.algal.2019.101713] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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16
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Alternative outlets for sustaining photosynthetic electron transport during dark-to-light transitions. Proc Natl Acad Sci U S A 2019; 116:11518-11527. [PMID: 31101712 PMCID: PMC6561286 DOI: 10.1073/pnas.1903185116] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Most forms of life on Earth cannot exist without photosynthesis. Our food and atmosphere depend on it. To obtain high photosynthetic yields, light energy must be efficiently coupled to the fixation of CO2 into organic molecules. Suboptimal environmental conditions can severely impact the conversion of light energy to biomass and lead to reactive oxygen production, which in turn can cause cellular damage and loss of productivity. Hence, plants, algae, and photosynthetic bacteria have evolved a network of alternative outlets to sustain the flow of photosynthetically derived electrons. Our work is focused on the nature and integration of these outlets, which will inform a rational engineering of crop plants and algae to optimize photosynthesis and meet the increased global demand for food. Environmental stresses dramatically impact the balance between the production of photosynthetically derived energetic electrons and Calvin–Benson–Bassham cycle (CBBC) activity; an imbalance promotes accumulation of reactive oxygen species and causes cell damage. Hence, photosynthetic organisms have developed several strategies to route electrons toward alternative outlets that allow for storage or harmless dissipation of their energy. In this work, we explore the activities of three essential outlets associated with Chlamydomonas reinhardtii photosynthetic electron transport: (i) reduction of O2 to H2O through flavodiiron proteins (FLVs) and (ii) plastid terminal oxidases (PTOX) and (iii) the synthesis of starch. Real-time measurements of O2 exchange have demonstrated that FLVs immediately engage during dark-to-light transitions, allowing electron transport when the CBBC is not fully activated. Under these conditions, we quantified maximal FLV activity and its overall capacity to direct photosynthetic electrons toward O2 reduction. However, when starch synthesis is compromised, a greater proportion of the electrons is directed toward O2 reduction through both the FLVs and PTOX, suggesting an important role for starch synthesis in priming/regulating CBBC and electron transport. Moreover, partitioning energized electrons between sustainable (starch; energetic electrons are recaptured) and nonsustainable (H2O; energetic electrons are not recaptured) outlets is part of the energy management strategy of photosynthetic organisms that allows them to cope with the fluctuating conditions encountered in nature. Finally, unmasking the repertoire and control of such energetic reactions offers new directions for rational redesign and optimization of photosynthesis to satisfy global demands for food and other resources.
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17
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Kulk G, Buist A, van de Poll WH, Rozema PD, Buma AGJ. Size scaling of photophysiology and growth in four freshly isolated diatom species from Ryder Bay, western Antarctic peninsula. JOURNAL OF PHYCOLOGY 2019; 55:314-328. [PMID: 30449029 PMCID: PMC6590143 DOI: 10.1111/jpy.12813] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Accepted: 10/19/2018] [Indexed: 06/09/2023]
Abstract
Diatoms are one of the dominant groups in phytoplankton communities of the western Antarctic Peninsula (WAP). Although generally well-studied, little is known about size dependent photophysiological responses in diatom bloom formation and succession. To increase this understanding, four Antarctic diatom species covering two orders of magnitude in cell size were isolated in northern Marguerite Bay (WAP). Fragilariopsis sp., Pseudo-nitzschia cf. subcurvata, Thalassiosira cf. antarctica, and Proboscia cf. alata were acclimated to three different irradiances after which photophysiology, electron transport, carbon fixation, and growth were assessed. The small species Fragilariopsis sp., Pseudo-nitzschia cf. subcurvata, and large species Proboscia cf. alata showed similar photoacclimation to higher irradiances with a decrease in cellular chlorophyll a and an increase in chlorophyll a specific absorption and xanthophyll cycle pigments and activity. In contrast, pigment concentrations and absorption remained unaffected by higher irradiances in the large species Thalassiosira cf. antarctica. Overall, the small species showed significantly higher growth rates compared to the large species, which was related to relatively high light harvesting capacity and electron transport rates in the smaller species. However, photophysiological responses related to photoinhibition and photoprotection and carbon fixation showed no relationship with cell size. This study supports the dominance of small diatoms at low irradiances during winter and early spring, but does not provide photophysiological evidence for the dominance of large diatoms during the phytoplankton bloom in the WAP. This suggests that other factors such as grazing and nutrient availability are likely to play a major role in diatom bloom formation.
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Affiliation(s)
- Gemma Kulk
- Department of Ocean EcosystemsEnergy and Sustainability Research Institute GroningenUniversity of GroningenNijenborgh 79747 AGGroningenthe Netherlands
| | - Anton Buist
- Department of Ocean EcosystemsEnergy and Sustainability Research Institute GroningenUniversity of GroningenNijenborgh 79747 AGGroningenthe Netherlands
| | - Willem H. van de Poll
- Department of Ocean EcosystemsEnergy and Sustainability Research Institute GroningenUniversity of GroningenNijenborgh 79747 AGGroningenthe Netherlands
| | - Patrick D. Rozema
- Department of Ocean EcosystemsEnergy and Sustainability Research Institute GroningenUniversity of GroningenNijenborgh 79747 AGGroningenthe Netherlands
| | - Anita G. J. Buma
- Department of Ocean EcosystemsEnergy and Sustainability Research Institute GroningenUniversity of GroningenNijenborgh 79747 AGGroningenthe Netherlands
- Arctic CentreFaculty of ArtsUniversity of GroningenAweg 309718 CWGroningenthe Netherlands
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18
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Hughes DJ, Campbell DA, Doblin MA, Kromkamp JC, Lawrenz E, Moore CM, Oxborough K, Prášil O, Ralph PJ, Alvarez MF, Suggett DJ. Roadmaps and Detours: Active Chlorophyll- a Assessments of Primary Productivity Across Marine and Freshwater Systems. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2018; 52:12039-12054. [PMID: 30247887 DOI: 10.1021/acs.est.8b03488] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Assessing phytoplankton productivity over space and time remains a core goal for oceanographers and limnologists. Fast Repetition Rate fluorometry (FRRf) provides a potential means to realize this goal with unprecedented resolution and scale yet has not become the "go-to" method despite high expectations. A major obstacle is difficulty converting electron transfer rates to equivalent rates of C-fixation most relevant for studies of biogeochemical C-fluxes. Such difficulty stems from methodological inconsistencies and our limited understanding of how the electron requirement for C-fixation (Φe,C) is influenced by the environment and by differences in the composition and physiology of phytoplankton assemblages. We outline a "roadmap" for limiting methodological bias and to develop a more mechanistic understanding of the ecophysiology underlying Φe,C. We 1) re-evaluate core physiological processes governing how microalgae invest photosynthetic electron transport-derived energy and reductant into stored carbon versus alternative sinks. Then, we 2) outline steps to facilitate broader uptake and exploitation of FRRf, which could transform our knowledge of aquatic primary productivity. We argue it is time to 3) revise our historic methodological focus on carbon as the currency of choice, to 4) better appreciate that electron transport fundamentally drives ecosystem biogeochemistry, modulates cell-to-cell interactions, and ultimately modifies community biomass and structure.
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Affiliation(s)
- David J Hughes
- Climate Change Cluster , University of Technology Sydney , Ultimo, Sydney 2007 , New South Wales , Australia
| | - Douglas A Campbell
- Department of Biology , Mount Allison University , Sackville , New Brunswick E4L 1E4 , Canada
| | - Martina A Doblin
- Climate Change Cluster , University of Technology Sydney , Ultimo, Sydney 2007 , New South Wales , Australia
| | - Jacco C Kromkamp
- Department of Estuarine and Delta Systems , NIOZ Royal Netherlands Institute for Sea Research and Utrecht University , P.O. Box 140, 4401 NT Yerseke , The Netherlands
| | - Evelyn Lawrenz
- Centre Algatech , Institute of Microbiology, Czech Academy of Sciences , Třeboň 379 81 , Czech Republic
| | - C Mark Moore
- Ocean and Earth Science , University of Southampton, National Oceanography Centre, Southampton , European Way , Southampton SO14 3ZH , U.K
| | | | - Ondřej Prášil
- Centre Algatech , Institute of Microbiology, Czech Academy of Sciences , Třeboň 379 81 , Czech Republic
| | - Peter J Ralph
- Climate Change Cluster , University of Technology Sydney , Ultimo, Sydney 2007 , New South Wales , Australia
| | - Marco F Alvarez
- Climate Change Cluster , University of Technology Sydney , Ultimo, Sydney 2007 , New South Wales , Australia
| | - David J Suggett
- Climate Change Cluster , University of Technology Sydney , Ultimo, Sydney 2007 , New South Wales , Australia
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19
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Gilbert M, Bährs H, Steinberg CEW, Wilhelm C. The artificial humic substance HS1500 does not inhibit photosynthesis of the green alga Desmodesmus armatus in vivo but interacts with the photosynthetic apparatus of isolated spinach thylakoids in vitro. PHOTOSYNTHESIS RESEARCH 2018; 137:403-420. [PMID: 29777430 DOI: 10.1007/s11120-018-0513-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2017] [Accepted: 05/01/2018] [Indexed: 06/08/2023]
Abstract
Humic substances (HSs) can influence the growth and composition of freshwater phytoplankton assemblage. Since HSs contain many phenolic and quinonic moieties and cause growth reductions in eco-physiological field experiments, HSs are considered photosystem II herbicides. To test this specific mode of action in vivo and in vitro, respectively, we used intact cells of the green alga Desmodesmus armatus, as well as thylakoids isolated from spinach (Spinacia oleracea) as a model system for the green algal chloroplast. Photosynthetic electron transport was measured as oxygen evolution and variable chlorophyll fluorescence. The in vivo effect of the artificial humic substance HS1500 on algae consisted of no impact on photosynthesis-irradiance curves of intact green algae compared to untreated controls. In contrast, addition of HS1500 to isolated thylakoids resulted in light-induced oxygen consumption (Mehler reaction) as an in vitro effect. Fluorescence induction kinetics of HS-treated thylakoids revealed a large static quenching effect of HS1500, but no inhibitory effect on electron transport. For the case of intact algal cells, we conclude that the highly hydrophilic and rather large molecules of HS1500 are not taken up in effective quantities and, therefore, cannot interfere with photosynthesis. The in vitro tests show that HS1500 has no inhibitory effect on photosystem II but operates as a weak, oxygen-consuming Hill acceptor at photosystem I. Hence, the results indicate that eco-physiological field experiments should focus more strongly on effects of HSs on extracellular features, such as reducing and red-shifting the underwater light field or influencing nutrient availability by cation exchange within the plankton network.
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Affiliation(s)
- Matthias Gilbert
- Institute of Biology, Department of Plant Physiology, University of Leipzig, Johannisallee 21-23, 04103, Leipzig, Germany.
| | - Hanno Bährs
- Aquacopa GmbH, Koppelbergstr. 4, 17166, Teterow, Germany
| | - Christian E W Steinberg
- Department of Biology, Freshwater and Stress Ecology, Humboldt-University Berlin, Arboretum, Späthstraße 80/81, 12437, Berlin, Germany
| | - Christian Wilhelm
- Institute of Biology, Department of Plant Physiology, University of Leipzig, Johannisallee 21-23, 04103, Leipzig, Germany.
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20
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Hippmann AA, Schuback N, Moon KM, McCrow JP, Allen AE, Foster LJ, Green BR, Maldonado MT. Contrasting effects of copper limitation on the photosynthetic apparatus in two strains of the open ocean diatom Thalassiosira oceanica. PLoS One 2017; 12:e0181753. [PMID: 28837661 PMCID: PMC5570362 DOI: 10.1371/journal.pone.0181753] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2017] [Accepted: 07/06/2017] [Indexed: 11/25/2022] Open
Abstract
There is an intricate interaction between iron (Fe) and copper (Cu) physiology in diatoms. However, strategies to cope with low Cu are largely unknown. This study unveils the comprehensive restructuring of the photosynthetic apparatus in the diatom Thalassiosira oceanica (CCMP1003) in response to low Cu, at the physiological and proteomic level. The restructuring results in a shift from light harvesting for photochemistry—and ultimately for carbon fixation—to photoprotection, reducing carbon fixation and oxygen evolution. The observed decreases in the physiological parameters Fv/Fm, carbon fixation, and oxygen evolution, concomitant with increases in the antennae absorption cross section (σPSII), non-photochemical quenching (NPQ) and the conversion factor (φe:C/ηPSII) are in agreement with well documented cellular responses to low Fe. However, the underlying proteomic changes due to low Cu are very different from those elicited by low Fe. Low Cu induces a significant four-fold reduction in the Cu-containing photosynthetic electron carrier plastocyanin. The decrease in plastocyanin causes a bottleneck within the photosynthetic electron transport chain (ETC), ultimately leading to substantial stoichiometric changes. Namely, 2-fold reduction in both cytochrome b6f complex (cytb6f) and photosystem II (PSII), no change in the Fe-rich PSI and a 40- and 2-fold increase in proteins potentially involved in detoxification of reactive oxygen species (ferredoxin and ferredoxin:NADP+ reductase, respectively). Furthermore, we identify 48 light harvesting complex (LHC) proteins in the publicly available genome of T. oceanica and provide proteomic evidence for 33 of these. The change in the LHC composition within the antennae in response to low Cu underlines the shift from photochemistry to photoprotection in T. oceanica (CCMP1003). Interestingly, we also reveal very significant intra-specific strain differences. Another strain of T. oceanica (CCMP 1005) requires significantly higher Cu concentrations to sustain both its maximal and minimal growth rate compared to CCMP 1003. Under low Cu, CCMP 1005 decreases its growth rate, cell size, Chla and total protein per cell. We argue that the reduction in protein per cell is the main strategy to decrease its cellular Cu requirement, as none of the other parameters tested are affected. Differences between the two strains, as well as differences between the well documented responses to low Fe and those presented here in response to low Cu are discussed.
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Affiliation(s)
- Anna A. Hippmann
- Department of Earth, Ocean, and Atmospheric Sciences, University of British Columbia, Vancouver, British Columbia, Canada
- * E-mail: (AAH); (MTM)
| | - Nina Schuback
- Department of Earth, Ocean, and Atmospheric Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Kyung-Mee Moon
- Department of Biochemistry & Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada
| | - John P. McCrow
- Department of Microbial & Environmental Genomics, J. Craig Venter Institute, La Jolla, California, United States of America
| | - Andrew E. Allen
- Department of Microbial & Environmental Genomics, J. Craig Venter Institute, La Jolla, California, United States of America
| | - Leonard J. Foster
- Department of Biochemistry & Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Beverley R. Green
- Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada
| | - Maria T. Maldonado
- Department of Earth, Ocean, and Atmospheric Sciences, University of British Columbia, Vancouver, British Columbia, Canada
- * E-mail: (AAH); (MTM)
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21
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Photosystem II-cyclic electron flow powers exceptional photoprotection and record growth in the microalga Chlorella ohadii. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2017; 1858:873-883. [PMID: 28734933 DOI: 10.1016/j.bbabio.2017.07.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Revised: 07/12/2017] [Accepted: 07/14/2017] [Indexed: 01/13/2023]
Abstract
The desert microalga Chlorella ohadii was reported to grow at extreme light intensities with minimal photoinhibition, tolerate frequent de/re-hydrations, yet minimally employs antenna-based non-photochemical quenching for photoprotection. Here we investigate the molecular mechanisms by measuring Photosystem II charge separation yield (chlorophyll variable fluorescence, Fv/Fm) and flash-induced O2 yield to measure the contributions from both linear (PSII-LEF) and cyclic (PSII-CEF) electron flow within PSII. Cells grow increasingly faster at higher light intensities (μE/m2/s) from low (20) to high (200) to extreme (2000) by escalating photoprotection via shifting from PSII-LEF to PSII-CEF. This shifts PSII charge separation from plastoquinone reduction (PSII-LEF) to plastoquinol oxidation (PSII-CEF), here postulated to enable proton gradient and ATP generation that powers photoprotection. Low light-grown cells have unusually small antennae (332 Chl/PSII), use mainly PSII-LEF (95%) and convert 40% of PSII charge separations into O2 (a high O2 quantum yield of 0.06mol/mol PSII/flash). High light-grown cells have smaller antenna and lower PSII-LEF (63%). Extreme light-grown cells have only 42 Chl/PSII (no LHCII antenna), minimal PSII-LEF (10%), and grow faster than any known phototroph (doubling time 1.3h). Adding a synthetic quinone in excess to supplement the PQ pool fully uncouples PSII-CEF from its natural regulation and produces maximum PSII-LEF. Upon dark adaptation PSII-LEF rapidly reverts to PSII-CEF, a transient protection mechanism to conserve water and minimize the cost of antenna biosynthesis. The capacity of the electron acceptor pool (plastoquinone pool), and the characteristic times for exchange of (PQH2)B with PQpool and reoxidation of (PQH2)pool were determined.
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Gates C, Ananyev G, Dismukes GC. The strontium inorganic mutant of the water oxidizing center (CaMn4O5) of PSII improves WOC efficiency but slows electron flux through the terminal acceptors. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1857:1550-1560. [DOI: 10.1016/j.bbabio.2016.06.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2016] [Revised: 05/26/2016] [Accepted: 06/10/2016] [Indexed: 01/26/2023]
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Jerez CG, Malapascua JR, Sergejevová M, Masojídek J, Figueroa FL. Chlorella fusca (Chlorophyta) grown in thin-layer cascades: Estimation of biomass productivity by in-vivo chlorophyll a fluorescence monitoring. ALGAL RES 2016. [DOI: 10.1016/j.algal.2016.04.010] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Jin P, Gao G, Liu X, Li F, Tong S, Ding J, Zhong Z, Liu N, Gao K. Contrasting Photophysiological Characteristics of Phytoplankton Assemblages in the Northern South China Sea. PLoS One 2016; 11:e0153555. [PMID: 27195824 PMCID: PMC4873168 DOI: 10.1371/journal.pone.0153555] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Accepted: 03/31/2016] [Indexed: 12/11/2022] Open
Abstract
The growth of phytoplankton and thus marine primary productivity depend on photophysiological performance of phytoplankton cells that respond to changing environmental conditions. The South China Sea (SCS) is the largest marginal sea of the western Pacific and plays important roles in modulating regional climate and carbon budget. However, little has been documented on photophysiological characteristics of phytoplankton in the SCS. For the first time, we investigated photophysiological characteristics of phytoplankton assemblages in the northern South China Sea (NSCS) using a real-time in-situ active chlorophyll a fluorometry, covering 4.0 × 105 km2. The functional absorption cross section of photosystem II (PSII) in darkness (σPSII) or under ambient light (σPSII’) (A2 quanta-1) increased from the surface to deeper waters at all the stations during the survey period (29 July to 23 August 2012). While the maximum (Fv/Fm, measured in darkness) or effective (Fq’/Fm’, measured under ambient light) photochemical efficiency of PSII appeared to increase with increasing depth at most stations, it showed inverse relationship with depth in river plume areas. The functional absorption cross section of PSII changes could be attributed to light-adapted genotypic feature due to niche-partition and the alteration of photochemical efficiency of PSII could be attributed to photo-acclimation. The chlorophyll a fluorometry can be taken as an analog to estimate primary productivity, since areas of higher photochemical efficiency of PSII coincided with those of higher primary productivity reported previously in the NSCS.
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Affiliation(s)
- Peng Jin
- State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, China
| | - Guang Gao
- State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, China
| | - Xin Liu
- State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, China
| | - Futian Li
- State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, China
| | - Shanying Tong
- State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, China
| | - Jiancheng Ding
- State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, China
| | - Zhihai Zhong
- Marine Biology Institute, Shantou University, Shantou, Guangdong 515063, China
| | - Nana Liu
- State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, China
| | - Kunshan Gao
- State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, China
- * E-mail:
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Yamori W. Photosynthetic response to fluctuating environments and photoprotective strategies under abiotic stress. JOURNAL OF PLANT RESEARCH 2016; 129:379-95. [PMID: 27023791 DOI: 10.1007/s10265-016-0816-1] [Citation(s) in RCA: 109] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Accepted: 03/06/2016] [Indexed: 05/18/2023]
Abstract
Plants in natural environments must cope with diverse, highly dynamic, and unpredictable conditions. They have mechanisms to enhance the capture of light energy when light intensity is low, but they can also slow down photosynthetic electron transport to prevent the production of reactive oxygen species and consequent damage to the photosynthetic machinery under excess light. Plants need a highly responsive regulatory system to balance the photosynthetic light reactions with downstream metabolism. Various mechanisms of regulation of photosynthetic electron transport under stress have been proposed, however the data have been obtained mainly under environmentally stable and controlled conditions. Thus, our understanding of dynamic modulation of photosynthesis under dramatically fluctuating natural environments remains limited. In this review, first I describe the magnitude of environmental fluctuations under natural conditions. Next, I examine the effects of fluctuations in light intensity, CO2 concentration, leaf temperature, and relative humidity on dynamic photosynthesis. Finally, I summarize photoprotective strategies that allow plants to maintain the photosynthesis under stressful fluctuating environments. The present work clearly showed that fluctuation in various environmental factors resulted in reductions in photosynthetic rate in a stepwise manner at every environmental fluctuation, leading to the conclusion that fluctuating environments would have a large impact on photosynthesis.
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Affiliation(s)
- Wataru Yamori
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7‑3‑1 Hongo, Bunkyo‑ku, Tokyo, 113-0033, Japan.
- Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012, Japan.
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Yamori W, Shikanai T. Physiological Functions of Cyclic Electron Transport Around Photosystem I in Sustaining Photosynthesis and Plant Growth. ANNUAL REVIEW OF PLANT BIOLOGY 2016; 67:81-106. [PMID: 26927905 DOI: 10.1146/annurev-arplant-043015-112002] [Citation(s) in RCA: 285] [Impact Index Per Article: 35.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
The light reactions in photosynthesis drive both linear and cyclic electron transport around photosystem I (PSI). Linear electron transport generates both ATP and NADPH, whereas PSI cyclic electron transport produces ATP without producing NADPH. PSI cyclic electron transport is thought to be essential for balancing the ATP/NADPH production ratio and for protecting both photosystems from damage caused by stromal overreduction. Two distinct pathways of cyclic electron transport have been proposed in angiosperms: a major pathway that depends on the PROTON GRADIENT REGULATION 5 (PGR5) and PGR5-LIKE PHOTOSYNTHETIC PHENOTYPE 1 (PGRL1) proteins, which are the target site of antimycin A, and a minor pathway mediated by the chloroplast NADH dehydrogenase-like (NDH) complex. Recently, the regulation of PSI cyclic electron transport has been recognized as essential for photosynthesis and plant growth. In this review, we summarize the possible functions and importance of the two pathways of PSI cyclic electron transport.
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Affiliation(s)
- Wataru Yamori
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan;
- Precursory Research for Embryonic Science and Technology (PRESTO) and
| | - Toshiharu Shikanai
- Core Research for Evolutionary Science and Technology (CREST), Japan Science and Technology Agency, Kawaguchi 332-0012, Japan
- Department of Botany, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
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Ananyev G, Gates C, Dismukes GC. The Oxygen quantum yield in diverse algae and cyanobacteria is controlled by partitioning of flux between linear and cyclic electron flow within photosystem II. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1857:1380-1391. [PMID: 27117512 DOI: 10.1016/j.bbabio.2016.04.056] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2015] [Revised: 04/20/2016] [Accepted: 04/21/2016] [Indexed: 01/07/2023]
Abstract
We have measured flash-induced oxygen quantum yields (O2-QYs) and primary charge separation (Chl variable fluorescence yield, Fv/Fm) in vivo among phylogenetically diverse microalgae and cyanobacteria. Higher O2-QYs can be attained in cells by releasing constraints on charge transfer at the Photosystem II (PSII) acceptor side by adding membrane-permeable benzoquinone (BQ) derivatives that oxidize plastosemiquinone QB(-) and QBH2. This method allows uncoupling PSII turnover from its natural regulation in living cells, without artifacts of isolating PSII complexes. This approach reveals different extents of regulation across species, controlled at the QB(-) acceptor site. Arthrospira maxima is confirmed as the most efficient PSII-WOC (water oxidizing complex) and exhibits the least regulation of flux. Thermosynechococcus elongatus exhibits an O2-QY of 30%, suggesting strong downregulation. WOC cycle simulations with the most accurate model (VZAD) show that a light-driven backward transition (net addition of an electron to the WOC, distinct from recombination) occurs in up to 25% of native PSIIs in the S2 and S3 states, while adding BQ prevents backward transitions and increases the lifetime of S2 and S3 by 10-fold. Backward transitions occur in PSIIs that have plastosemiquinone radicals in the QB site and are postulated to be physiologically regulated pathways for storing light energy as proton gradient through direct PSII-cyclic electron flow (PSII-CEF). PSII-CEF is independent of classical PSI/cyt-b6f-CEF and provides an alternative proton translocation pathway for energy conversion. PSII-CEF enables variable fluxes between linear and cyclic electron pathways, thus accommodating species-dependent needs for redox and ion-gradient energy sources powered by a single photosystem.
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Affiliation(s)
- Gennady Ananyev
- The Waksman Institute of Microbiology and the Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, NJ 08854, United States
| | - Colin Gates
- The Waksman Institute of Microbiology and the Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, NJ 08854, United States
| | - G Charles Dismukes
- The Waksman Institute of Microbiology and the Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, NJ 08854, United States.
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Interacting Effects of Light and Iron Availability on the Coupling of Photosynthetic Electron Transport and CO2-Assimilation in Marine Phytoplankton. PLoS One 2015; 10:e0133235. [PMID: 26171963 PMCID: PMC4501554 DOI: 10.1371/journal.pone.0133235] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2015] [Accepted: 06/25/2015] [Indexed: 12/30/2022] Open
Abstract
Iron availability directly affects photosynthesis and limits phytoplankton growth over vast oceanic regions. For this reason, the availability of iron is a crucial variable to consider in the development of active chlorophyll a fluorescence based estimates of phytoplankton primary productivity. These bio-optical approaches require a conversion factor to derive ecologically-relevant rates of CO2-assimilation from estimates of electron transport in photosystem II. The required conversion factor varies significantly across phytoplankton taxa and environmental conditions, but little information is available on its response to iron limitation. In this study, we examine the role of iron limitation, and the interacting effects of iron and light availability, on the coupling of photosynthetic electron transport and CO2-assimilation in marine phytoplankton. Our results show that excess irradiance causes increased decoupling of carbon fixation and electron transport, particularly under iron limiting conditions. We observed that reaction center II specific rates of electron transport (ETRRCII, mol e- mol RCII-1 s-1) increased under iron limitation, and we propose a simple conceptual model for this observation. We also observed a strong correlation between the derived conversion factor and the expression of non-photochemical quenching. Utilizing a dataset from in situ phytoplankton assemblages across a coastal – oceanic transect in the Northeast subarctic Pacific, this relationship was used to predict ETRRCII: CO2-assimilation conversion factors and carbon-based primary productivity from FRRF data, without the need for any additional measurements.
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Hoppe CJM, Holtz L, Trimborn S, Rost B. Ocean acidification decreases the light-use efficiency in an Antarctic diatom under dynamic but not constant light. THE NEW PHYTOLOGIST 2015; 207:159-171. [PMID: 25708812 PMCID: PMC4950296 DOI: 10.1111/nph.13334] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2014] [Accepted: 01/12/2015] [Indexed: 05/07/2023]
Abstract
There is increasing evidence that different light intensities strongly modulate the effects of ocean acidification (OA) on marine phytoplankton. The aim of the present study was to investigate interactive effects of OA and dynamic light, mimicking natural mixing regimes. The Antarctic diatom Chaetoceros debilis was grown under two pCO2 (390 and 1000 μatm) and light conditions (constant and dynamic), the latter yielding the same integrated irradiance over the day. To characterize interactive effects between treatments, growth, elemental composition, primary production and photophysiology were investigated. Dynamic light reduced growth and strongly altered the effects of OA on primary production, being unaffected by elevated pCO2 under constant light, yet significantly reduced under dynamic light. Interactive effects between OA and light were also observed for Chl production and particulate organic carbon quotas. Response patterns can be explained by changes in the cellular energetic balance. While the energy transfer efficiency from photochemistry to biomass production (Φe,C ) was not affected by OA under constant light, it was drastically reduced under dynamic light. Contrasting responses under different light conditions need to be considered when making predictions regarding a more stratified and acidified future ocean.
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Affiliation(s)
- Clara J. M. Hoppe
- Alfred Wegener Institute – Helmholtz Centre for Polar and Marine ResearchAm Handelshafen 12Bremerhaven27570Germany
| | - Lena‐Maria Holtz
- Alfred Wegener Institute – Helmholtz Centre for Polar and Marine ResearchAm Handelshafen 12Bremerhaven27570Germany
| | - Scarlett Trimborn
- Alfred Wegener Institute – Helmholtz Centre for Polar and Marine ResearchAm Handelshafen 12Bremerhaven27570Germany
- University BremenLeobener Straße NW2‐ABremen28359Germany
| | - Björn Rost
- Alfred Wegener Institute – Helmholtz Centre for Polar and Marine ResearchAm Handelshafen 12Bremerhaven27570Germany
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Hamdani S, Qu M, Xin CP, Li M, Chu C, Zhu XG. Variations between the photosynthetic properties of elite and landrace Chinese rice cultivars revealed by simultaneous measurements of 820 nm transmission signal and chlorophyll a fluorescence induction. JOURNAL OF PLANT PHYSIOLOGY 2015; 177:128-138. [PMID: 25732386 DOI: 10.1016/j.jplph.2014.12.019] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Revised: 11/21/2014] [Accepted: 12/08/2014] [Indexed: 06/04/2023]
Abstract
The difference between the photosynthetic properties of elite and landrace Chinese rice cultivars was studied, using chlorophyll a fluorescence induction (mostly a monitor of Photosystem II activity) and I820 transmission signal (mostly a monitor of Photosystem I activity) to identify potential photosynthetic features differentiating these two groups, which show different degrees of artificial selection and grain yields. A higher fluorescence (related to PSII) IP rise phase and a lower P700(+) (related to PSI) accumulation were observed in the elite cultivars as compared to the landraces. Using these data, together with simulation data from a kinetic model of fluorescence induction, we show that the high IP rise phase and the low P700(+) accumulation can be a result of transient block on electron transfer and traffic jam on the electron acceptor side of PSI under a high [NADPH]/[NADP(+)] ratio. Considering that the ferredoxin NADP(+) reductase (FNR) transcript levels of XS134 (a representative elite cultivars) remains unaffected during the first few minutes of light/dark transition compared to Q4145 (a representative landrace cultivars), which shows a strong decline during the same time range, we propose that the FNR of elite cultivars may take more time to be inactivated in darkness. During this time the FNR enzyme can continue to reduce NADP(+) molecules, leading to initially high [NADPH]/[NADP(+)] ratio during OJIP transient. These data suggested a potential artificial selection of FNR during the breeding process of these examined elite rice cultivars.
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Affiliation(s)
- Saber Hamdani
- CAS Key Laboratory of Computational Biology, Partner Institute for Computational Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Mingnan Qu
- CAS Key Laboratory of Computational Biology, Partner Institute for Computational Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Chang-Peng Xin
- CAS Key Laboratory of Computational Biology, Partner Institute for Computational Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Ming Li
- CAS Key Laboratory of Computational Biology, Partner Institute for Computational Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Chengcai Chu
- Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
| | - Xin-Guang Zhu
- CAS Key Laboratory of Computational Biology, Partner Institute for Computational Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
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Roberty S, Bailleul B, Berne N, Franck F, Cardol P. PSI Mehler reaction is the main alternative photosynthetic electron pathway in Symbiodinium sp., symbiotic dinoflagellates of cnidarians. THE NEW PHYTOLOGIST 2014; 204:81-91. [PMID: 24975027 DOI: 10.1111/nph.12903] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2014] [Accepted: 05/17/2014] [Indexed: 05/04/2023]
Abstract
Photosynthetic organisms have developed various photoprotective mechanisms to cope with exposure to high light intensities. In photosynthetic dinoflagellates that live in symbiosis with cnidarians, the nature and relative amplitude of these regulatory mechanisms are a matter of debate. In our study, the amplitude of photosynthetic alternative electron flows (AEF) to oxygen (chlororespiration, Mehler reaction), the mitochondrial respiration and the Photosystem I (PSI) cyclic electron flow were investigated in strains belonging to three clades (A1, B1 and F1) of Symbiodinium. Cultured Symbiodinium strains were maintained under identical environmental conditions, and measurements of oxygen evolution, fluorescence emission and absorption changes at specific wavelengths were used to evaluate PSI and PSII electron transfer rates (ETR). A light- and O2 -dependent ETR was observed in all strains. This electron transfer chain involves PSII and PSI and is insensitive to inhibitors of mitochondrial activity and carbon fixation. We demonstrate that in all strains, the Mehler reaction responsible for photoreduction of oxygen by the PSI under high light, is the main AEF at the onset and at the steady state of photosynthesis. This sustained photosynthetic AEF under high light intensities acts as a photoprotective mechanism and leads to an increase of the ATP/NADPH ratio.
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Affiliation(s)
- Stéphane Roberty
- Laboratoire d'Ecologie Animale et d'Ecotoxicologie, Département de Biologie, Ecologie et Evolution, Université de Liège, 11 Allée du 6 Août, B-4000, Liège, Belgium
- Laboratoire de Bioénergétique, Institut de Botanique, Université de Liège, 27 Bld du Rectorat, B-4000, Liège, Belgium
| | - Benjamin Bailleul
- Laboratoire de Génétique et Physiologie des Microalgues, Institut de Botanique, Université de Liège, 27 Bld du Rectorat, B-4000, Liège, Belgium
| | - Nicolas Berne
- Laboratoire de Génétique et Physiologie des Microalgues, Institut de Botanique, Université de Liège, 27 Bld du Rectorat, B-4000, Liège, Belgium
| | - Fabrice Franck
- Laboratoire de Bioénergétique, Institut de Botanique, Université de Liège, 27 Bld du Rectorat, B-4000, Liège, Belgium
- PhytoSYSTEMS, Université de Liège, B-4000, Liège, Belgium
| | - Pierre Cardol
- Laboratoire de Génétique et Physiologie des Microalgues, Institut de Botanique, Université de Liège, 27 Bld du Rectorat, B-4000, Liège, Belgium
- PhytoSYSTEMS, Université de Liège, B-4000, Liège, Belgium
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Schansker G, Tóth SZ, Holzwarth AR, Garab G. Chlorophyll a fluorescence: beyond the limits of the Q(A) model. PHOTOSYNTHESIS RESEARCH 2014; 120:43-58. [PMID: 23456268 DOI: 10.1007/s11120-013-9806-5] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2012] [Accepted: 02/18/2013] [Indexed: 05/03/2023]
Abstract
Chlorophyll a fluorescence is a non-invasive tool widely used in photosynthesis research. According to the dominant interpretation, based on the model proposed by Duysens and Sweers (1963, Special Issue of Plant and Cell Physiology, pp 353-372), the fluorescence changes reflect primarily changes in the redox state of Q(A), the primary quinone electron acceptor of photosystem II (PSII). While it is clearly successful in monitoring the photochemical activity of PSII, a number of important observations cannot be explained within the framework of this simple model. Alternative interpretations have been proposed but were not supported satisfactorily by experimental data. In this review we concentrate on the processes determining the fluorescence rise on a dark-to-light transition and critically analyze the experimental data and the existing models. Recent experiments have provided additional evidence for the involvement of a second process influencing the fluorescence rise once Q(A) is reduced. These observations are best explained by a light-induced conformational change, the focal point of our review. We also want to emphasize that-based on the presently available experimental findings-conclusions on α/ß-centers, PSII connectivity, and the assignment of FV/FM to the maximum PSII quantum yield may require critical re-evaluations. At the same time, it has to be emphasized that for a deeper understanding of the underlying physical mechanism(s) systematic studies on light-induced changes in the structure and reaction kinetics of the PSII reaction center are required.
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Affiliation(s)
- Gert Schansker
- Institute of Plant Biology, Biological Research Center Szeged, Hungarian Academy of Sciences, Szeged, 6701, Hungary,
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Schuurmans RM, Schuurmans JM, Bekker M, Kromkamp JC, Matthijs HC, Hellingwerf KJ. The redox potential of the plastoquinone pool of the cyanobacterium Synechocystis species strain PCC 6803 is under strict homeostatic control. PLANT PHYSIOLOGY 2014; 165:463-75. [PMID: 24696521 PMCID: PMC4012603 DOI: 10.1104/pp.114.237313] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
A method is presented for rapid extraction of the total plastoquinone (PQ) pool from Synechocystis sp. strain PCC 6803 cells that preserves the in vivo plastoquinol (PQH2) to -PQ ratio. Cells were rapidly transferred into ice-cold organic solvent for instantaneous extraction of the cellular PQ plus PQH2 content. After high-performance liquid chromatography fractionation of the organic phase extract, the PQH2 content was quantitatively determined via its fluorescence emission at 330 nm. The in-cell PQH2-PQ ratio then followed from comparison of the PQH2 signal in samples as collected and in an identical sample after complete reduction with sodium borohydride. Prior to PQH2 extraction, cells from steady-state chemostat cultures were exposed to a wide range of physiological conditions, including high/low availability of inorganic carbon, and various actinic illumination conditions. Well-characterized electron-transfer inhibitors were used to generate a reduced or an oxidized PQ pool for reference. The in vivo redox state of the PQ pool was correlated with the results of pulse-amplitude modulation-based chlorophyll a fluorescence emission measurements, oxygen exchange rates, and 77 K fluorescence emission spectra. Our results show that the redox state of the PQ pool of Synechocystis sp. strain PCC 6803 is subject to strict homeostatic control (i.e. regulated between narrow limits), in contrast to the more dynamic chlorophyll a fluorescence signal.
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Ihnken S, Kromkamp JC, Beardall J, Silsbe GM. State-transitions facilitate robust quantum yields and cause an over-estimation of electron transport in Dunaliella tertiolecta cells held at the CO₂ compensation point and re-supplied with DIC. PHOTOSYNTHESIS RESEARCH 2014; 119:257-272. [PMID: 24135997 DOI: 10.1007/s11120-013-9937-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2013] [Accepted: 10/01/2013] [Indexed: 06/02/2023]
Abstract
Photosynthetic energy consumption and non-photosynthetic energy quenching processes are inherently linked. Both processes must be controlled by the cell to allow cell maintenance and growth, but also to avoid photodamage. We used the chlorophyte algae Dunaliella tertiolecta to investigate how the interactive regulation of photosynthetic and non-photosynthetic pathways varies along dissolved inorganic carbon (DIC) and photon flux gradients. Specifically, cells were transferred to DIC-deplete media to reach a CO₂ compensation before being re-supplied with DIC at various concentrations and different photon flux levels. Throughout these experiments we monitored and characterized the photophysiological responses using pulse amplitude modulated fluorescence, oxygen evolution, 77 K fluorescence emission spectra, and fast-repetition rate fluorometry. O₂ uptake was not significantly stimulated at DIC depletion, which suggests that O₂ production rates correspond to assimilatory photosynthesis. Fluorescence-based measures of relative electron transport rates (rETRs) over-estimated oxygen-based photosynthetic measures due to a strong state-transitional response that facilitated high effective quantum yields. Adoption of an alternative fluorescence-based rETR calculation that accounts for state-transitions resulted in improved linear oxygen versus rETR correlation. This study shows the extraordinary capacity of D. tertiolecta to maintain stable effective quantum yields by flexible regulation of state-transitions. Uncertainties about the control mechanisms of state-transitions are presented.
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Affiliation(s)
- Sven Ihnken
- Netherlands Institute for Sea Research, NIOZ, Postbus 140, 4400 AC, Yerseke, The Netherlands
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35
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Havaux M. Probing Electron Transport through and around Photosystem II in vivo by the Combined Use of Photoacoustic Spectroscopy and Chlorophyll Fluorometry. Isr J Chem 2013. [DOI: 10.1002/ijch.199800027] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Park JJ, Lechno-Yossef S, Wolk CP, Vieille C. Cell-specific gene expression in Anabaena variabilis grown phototrophically, mixotrophically, and heterotrophically. BMC Genomics 2013; 14:759. [PMID: 24191963 PMCID: PMC4046671 DOI: 10.1186/1471-2164-14-759] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2013] [Accepted: 10/26/2013] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND When the filamentous cyanobacterium Anabaena variabilis grows aerobically without combined nitrogen, some vegetative cells differentiate into N2-fixing heterocysts, while the other vegetative cells perform photosynthesis. Microarrays of sequences within protein-encoding genes were probed with RNA purified from extracts of vegetative cells, from isolated heterocysts, and from whole filaments to investigate transcript levels, and carbon and energy metabolism, in vegetative cells and heterocysts in phototrophic, mixotrophic, and heterotrophic cultures. RESULTS Heterocysts represent only 5% to 10% of cells in the filaments. Accordingly, levels of specific transcripts in vegetative cells were with few exceptions very close to those in whole filaments and, also with few exceptions (e.g., nif1 transcripts), levels of specific transcripts in heterocysts had little effect on the overall level of those transcripts in filaments. In phototrophic, mixotrophic, and heterotrophic growth conditions, respectively, 845, 649, and 846 genes showed more than 2-fold difference (p < 0.01) in transcript levels between vegetative cells and heterocysts. Principal component analysis showed that the culture conditions tested affected transcript patterns strongly in vegetative cells but much less in heterocysts. Transcript levels of the genes involved in phycobilisome assembly, photosynthesis, and CO2 assimilation were high in vegetative cells in phototrophic conditions, and decreased when fructose was provided. Our results suggest that Gln, Glu, Ser, Gly, Cys, Thr, and Pro can be actively produced in heterocysts. Whether other protein amino acids are synthesized in heterocysts is unclear. Two possible components of a sucrose transporter were identified that were upregulated in heterocysts in two growth conditions. We consider it likely that genes with unknown function represent a larger fraction of total transcripts in heterocysts than in vegetative cells across growth conditions. CONCLUSIONS This study provides the first comparison of transcript levels in heterocysts and vegetative cells from heterocyst-bearing filaments of Anabaena. Although the data presented do not give a complete picture of metabolism in either type of cell, they provide a metabolic scaffold on which to build future analyses of cell-specific processes and of the interactions of the two types of cells.
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Affiliation(s)
- Jeong-Jin Park
- />Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824 USA
- />Department of Microbiology & Molecular Genetics, Michigan State University, East Lansing, MI 48824 USA
- />Present address: Institute of Biological Chemistry, Washington State University, Pullman, WA 99164 USA
| | - Sigal Lechno-Yossef
- />Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824 USA
- />MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI 48824 USA
| | - Coleman Peter Wolk
- />Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824 USA
- />MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI 48824 USA
- />Department of Plant Biology, Michigan State University, East Lansing, MI 48824 USA
| | - Claire Vieille
- />Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824 USA
- />Department of Microbiology & Molecular Genetics, Michigan State University, East Lansing, MI 48824 USA
- />Department of Biochemistry & Molecular Biology, Michigan State University, East Lansing, MI 48824 USA
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Vinyard DJ, Ananyev GM, Charles Dismukes G. Photosystem II: The Reaction Center of Oxygenic Photosynthesis. Annu Rev Biochem 2013; 82:577-606. [DOI: 10.1146/annurev-biochem-070511-100425] [Citation(s) in RCA: 279] [Impact Index Per Article: 25.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- David J. Vinyard
- Department of Chemistry and Chemical Biology and the Waksman Institute of Microbiology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854; ,
- Department of Chemistry, Princeton University, Princeton, New Jersey 08540;
| | - Gennady M. Ananyev
- Department of Chemistry and Chemical Biology and the Waksman Institute of Microbiology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854; ,
| | - G. Charles Dismukes
- Department of Chemistry and Chemical Biology and the Waksman Institute of Microbiology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854; ,
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Hennige SJ, Coyne KJ, MacIntyre H, Liefer J, Warner ME. The photobiology of Heterosigma akashiwo. Photoacclimation, diurnal periodicity, and its ability to rapidly exploit exposure to high light. JOURNAL OF PHYCOLOGY 2013; 49:349-360. [PMID: 27008521 DOI: 10.1111/jpy.12043] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2012] [Accepted: 12/14/2012] [Indexed: 06/05/2023]
Abstract
Periodic and seasonal exposure to high light is a common occurrence for many near-shore and estuarine phytoplankton. Rapid acclimatization to shifts in light may provide an axis by which some species of phytoplankton can outcompete other microalgae. Patterns of photoacclimation and photosynthetic capacity in the raphidophyte Heterosigma akashiwo (Hada) Hada ex Hara et Chihara isolated from the mid-Atlantic of the United States were followed in continuous cultures at low- and high-light intensities, followed by reciprocal shifts to the opposite light level. The maximum quantum yield (Fv /Fm ) as well as the photosynthetic cross-section (σPSII ) of photosystem II was higher in high-light cultures compared to low-light cultures. Significant diurnal variability in photochemistry and photoprotection was noted at both light levels, and high-light-acclimated cultures displayed greater variability in photoprotective pathways. When shifted from low to high light, there was only a slight and temporary decline in maximum quantum yield, while cell specific growth more than doubled within 24 h. Rapid acclimation to high light was facilitated by short-term photoprotection (nonphotochemical quenching), reduced PSII reaction center connectivity, and electron transport. Short-term increases in de-epoxidated xanthophyll pigments contributed to nonphotochemical protection, but lagged behind initial increases in nonphotochemical quenching and were not the primary pathway of photoprotection in this alga. By 48 h, photochemistry of cultures shifted from low to high light resembled long-term high-light-acclimated cultures. This isolate of H. akashiwo appears well poised to exploit rapid shifts in light by using unique cellular adjustments in light harvesting and photochemistry.
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Affiliation(s)
- Sebastian J Hennige
- Centre for Marine Biodiversity and Biotechnology, Heriot-Watt University, Edinburgh, EH14 4AS, UK
- College of Earth, Ocean and Environment, University of Delaware, 700 Pilottown Rd., Lewes, Deleware, 19958, USA
| | - Kathryn J Coyne
- College of Earth, Ocean and Environment, University of Delaware, 700 Pilottown Rd., Lewes, Deleware, 19958, USA
| | - Hugh MacIntyre
- Department of Oceanography, Dalhousie University, PO Box 15000, Halifax, Nova Scotia, B3H 4R2, Canada
| | - Justin Liefer
- Dauphin Island Sea Lab, 102 B Bienville Blvd., Dauphin Island, Alabama, 36528, USA
| | - Mark E Warner
- College of Earth, Ocean and Environment, University of Delaware, 700 Pilottown Rd., Lewes, Deleware, 19958, USA
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Vinyard DJ, Gimpel J, Ananyev GM, Cornejo MA, Golden SS, Mayfield SP, Dismukes GC. Natural variants of photosystem II subunit D1 tune photochemical fitness to solar intensity. J Biol Chem 2012; 288:5451-62. [PMID: 23271739 DOI: 10.1074/jbc.m112.394668] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Photosystem II (PSII) is composed of six core polypeptides that make up the minimal unit capable of performing the primary photochemistry of light-driven charge separation and water oxidation in all oxygenic phototrophs. The D1 subunit of this complex contains most of the ligating amino acid residues for the Mn(4)CaO(5) core of the water-oxidizing complex (WOC). Most cyanobacteria have 3-5 copies of the psbA gene coding for at least two isoforms of D1, whereas algae and plants have only one isoform. Synechococcus elongatus PCC 7942 contains two D1 isoforms; D1:1 is expressed under low light conditions, and D1:2 is up-regulated in high light or stress conditions. Using a heterologous psbA expression system in the green alga Chlamydomonas reinhardtii, we have measured growth rate, WOC cycle efficiency, and O(2) yield as a function of D1:1, D1:2, or the native algal D1 isoform. D1:1-PSII cells outcompete D1:2-PSII cells and accumulate more biomass in light-limiting conditions. However, D1:2-PSII cells easily outcompete D1:1-PSII cells at high light intensities. The native C. reinhardtii-PSII WOC cycles less efficiently at all light intensities and produces less O(2) than either cyanobacterial D1 isoform. D1:2-PSII makes more O(2) per saturating flash than D1:1-PSII, but it exhibits lower WOC cycling efficiency at low light intensities due to a 40% faster charge recombination rate in the S(3) state. These functional advantages of D1:1-PSII and D1:2-PSII at low and high light regimes, respectively, can be explained by differences in predicted redox potentials of PSII electron acceptors that control kinetic performance.
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Affiliation(s)
- David J Vinyard
- Department of Chemistry and Chemical Biology, State University of New Jersey, Piscataway, New Jersey 08854, USA
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Stirbet A. Chlorophyll a fluorescence induction: a personal perspective of the thermal phase, the J-I-P rise. PHOTOSYNTHESIS RESEARCH 2012; 113:15-61. [PMID: 22810945 DOI: 10.1007/s11120-012-9754-5] [Citation(s) in RCA: 157] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2012] [Accepted: 05/29/2012] [Indexed: 05/03/2023]
Abstract
The fast (up to 1 s) chlorophyll (Chl) a fluorescence induction (FI) curve, measured under saturating continuous light, has a photochemical phase, the O-J rise, related mainly to the reduction of Q(A), the primary electron acceptor plastoquinone of Photosystem II (PSII); here, the fluorescence rise depends strongly on the number of photons absorbed. This is followed by a thermal phase, the J-I-P rise, which disappears at subfreezing temperatures. According to the mainstream interpretation of the fast FI, the variable fluorescence originates from PSII antenna, and the oxidized Q(A) is the most important quencher influencing the O-J-I-P curve. As the reaction centers of PSII are gradually closed by the photochemical reduction of Q(A), Chl fluorescence, F, rises from the O level (the minimal level) to the P level (the peak); yet, the relationship between F and [Q(A) (-)] is not linear, due to the presence of other quenchers and modifiers. Several alternative theories have been proposed, which give different interpretations of the O-J-I-P transient. The main idea in these alternative theories is that in saturating light, Q(A) is almost completely reduced already at the end of the photochemical phase O-J, but the fluorescence yield is lower than its maximum value due to the presence of either a second quencher besides Q(A), or there is an another process quenching the fluorescence; in the second quencher hypothesis, this quencher is consumed (or the process of quenching the fluorescence is reversed) during the thermal phase J-I-P. In this review, we discuss these theories. Based on our critical examination, that includes pros and cons of each theory, as well mathematical modeling, we conclude that the mainstream interpretation of the O-J-I-P transient is the most credible one, as none of the alternative ideas provide adequate explanation or experimental proof for the almost complete reduction of Q(A) at the end of the O-J phase, and for the origin of the fluorescence rise during the thermal phase. However, we suggest that some of the factors influencing the fluorescence yield that have been proposed in these newer theories, as e.g., the membrane potential ΔΨ, as suggested by Vredenberg and his associates, can potentially contribute to modulate the O-J-I-P transient in parallel with the reduction of Q(A), through changes at the PSII antenna and/or at the reaction center, or, possibly, through the control of the oxidation-reduction of the PQ-pool, including proton transfer into the lumen, as suggested by Rubin and his associates. We present in this review our personal perspective mainly on our understanding of the thermal phase, the J-I-P rise during Chl a FI in plants and algae.
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Lepetit B, Goss R, Jakob T, Wilhelm C. Molecular dynamics of the diatom thylakoid membrane under different light conditions. PHOTOSYNTHESIS RESEARCH 2012; 111:245-57. [PMID: 21327535 DOI: 10.1007/s11120-011-9633-5] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2010] [Accepted: 02/01/2011] [Indexed: 05/25/2023]
Abstract
During the last years significant progress was achieved in unraveling molecular characteristics of the thylakoid membrane of different diatoms. With the present review it is intended to summarize the current knowledge about the structural and functional changes within the thylakoid membrane of diatoms acclimated to different light conditions. This aspect is addressed on the level of the organization and regulation of light-harvesting proteins, the dissipation of excessively absorbed light energy by the process of non-photochemical quenching, and the lipid composition of diatom thylakoid membranes. Finally, a working hypothesis of the domain formation of the diatom thylakoid membrane is presented to highlight the most prominent differences of heterokontic thylakoids in comparison to vascular plants and green algae during the acclimation to low and high light conditions.
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Affiliation(s)
- Bernard Lepetit
- CNRS UMR6250 'LIENSs', Institute for Coastal and Environmental Research (ILE), University of La Rochelle, 2 rue Olympe de Gouges, 17042, La Rochelle cedex, France
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42
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Alderkamp AC, Kulk G, Buma AGJ, Visser RJW, Van Dijken GL, Mills MM, Arrigo KR. THE EFFECT OF IRON LIMITATION ON THE PHOTOPHYSIOLOGY OF PHAEOCYSTIS ANTARCTICA (PRYMNESIOPHYCEAE) AND FRAGILARIOPSIS CYLINDRUS (BACILLARIOPHYCEAE) UNDER DYNAMIC IRRADIANCE(1). JOURNAL OF PHYCOLOGY 2012; 48:45-59. [PMID: 27009649 DOI: 10.1111/j.1529-8817.2011.01098.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
The effects of iron limitation on photoacclimation to dynamic irradiance were studied in Phaeocystis antarctica G. Karst. and Fragilariopsis cylindrus (Grunow) W. Krieg. in terms of growth rate, photosynthetic parameters, pigment composition, and fluorescence characteristics. Under dynamic light conditions mimicking vertical mixing below the euphotic zone, P. antarctica displayed higher growth rates than F. cylindrus both under iron (Fe)-replete and Fe-limiting conditions. Both species showed xanthophyll de-epoxidation that was accompanied by low levels of nonphotochemical quenching (NPQ) during the irradiance maximum of the light cycle. The potential for NPQ at light levels corresponding to full sunlight was substantial in both species and increased under Fe limitation in F. cylindrus. Although the decline in Fv /Fm under Fe limitation was similar in both species, the accompanying decrease in the maximum rate of photosynthesis and growth rate was much stronger in F. cylindrus. Analysis of the electron transport rates through PSII and on to carbon (C) fixation revealed a large potential for photoprotective cyclic electron transport (CET) in F. cylindrus, particularly under Fe limitation. Probably, CET aided the photoprotection in F. cylindrus, but it also reduced photosynthetic efficiency at higher light intensities. P. antarctica, on the other hand, was able to efficiently use electrons flowing through PSII for C fixation at all light levels, particularly under Fe limitation. Thus, Fe limitation enhanced the photophysiological differences between P. antarctica and diatoms, supporting field observations where P. antarctica is found to dominate deeply mixed water columns, whereas diatoms dominate shallower mixed layers.
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Affiliation(s)
- Anne-Carlijn Alderkamp
- Department of Ocean Ecosystems, Energy and Sustainability Research Institute, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands Department of Environmental Earth System Science, Stanford University, Stanford, California 94305, USADepartment of Ocean Ecosystems, Energy and Sustainability Research Institute, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The NetherlandsDepartment of Environmental Earth System Science, Stanford University, Stanford, California 94305, USA
| | - Gemma Kulk
- Department of Ocean Ecosystems, Energy and Sustainability Research Institute, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands Department of Environmental Earth System Science, Stanford University, Stanford, California 94305, USADepartment of Ocean Ecosystems, Energy and Sustainability Research Institute, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The NetherlandsDepartment of Environmental Earth System Science, Stanford University, Stanford, California 94305, USA
| | - Anita G J Buma
- Department of Ocean Ecosystems, Energy and Sustainability Research Institute, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands Department of Environmental Earth System Science, Stanford University, Stanford, California 94305, USADepartment of Ocean Ecosystems, Energy and Sustainability Research Institute, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The NetherlandsDepartment of Environmental Earth System Science, Stanford University, Stanford, California 94305, USA
| | - Ronald J W Visser
- Department of Ocean Ecosystems, Energy and Sustainability Research Institute, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands Department of Environmental Earth System Science, Stanford University, Stanford, California 94305, USADepartment of Ocean Ecosystems, Energy and Sustainability Research Institute, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The NetherlandsDepartment of Environmental Earth System Science, Stanford University, Stanford, California 94305, USA
| | - Gert L Van Dijken
- Department of Ocean Ecosystems, Energy and Sustainability Research Institute, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands Department of Environmental Earth System Science, Stanford University, Stanford, California 94305, USADepartment of Ocean Ecosystems, Energy and Sustainability Research Institute, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The NetherlandsDepartment of Environmental Earth System Science, Stanford University, Stanford, California 94305, USA
| | - Matthew M Mills
- Department of Ocean Ecosystems, Energy and Sustainability Research Institute, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands Department of Environmental Earth System Science, Stanford University, Stanford, California 94305, USADepartment of Ocean Ecosystems, Energy and Sustainability Research Institute, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The NetherlandsDepartment of Environmental Earth System Science, Stanford University, Stanford, California 94305, USA
| | - Kevin R Arrigo
- Department of Ocean Ecosystems, Energy and Sustainability Research Institute, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands Department of Environmental Earth System Science, Stanford University, Stanford, California 94305, USADepartment of Ocean Ecosystems, Energy and Sustainability Research Institute, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The NetherlandsDepartment of Environmental Earth System Science, Stanford University, Stanford, California 94305, USA
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Cardona T, Sedoud A, Cox N, Rutherford AW. Charge separation in photosystem II: a comparative and evolutionary overview. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2011; 1817:26-43. [PMID: 21835158 DOI: 10.1016/j.bbabio.2011.07.012] [Citation(s) in RCA: 245] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2011] [Revised: 07/22/2011] [Accepted: 07/23/2011] [Indexed: 10/17/2022]
Abstract
Our current understanding of the PSII reaction centre owes a great deal to comparisons to the simpler and better understood, purple bacterial reaction centre. Here we provide an overview of the similarities with a focus on charge separation and the electron acceptors. We go on to discuss some of the main differences between the two kinds of reaction centres that have been highlighted by the improving knowledge of PSII. We attempt to relate these differences to functional requirements of water splitting. Some are directly associated with that function, e.g. high oxidation potentials, while others are associated with regulation and protection against photodamage. The protective and regulatory functions are associated with the harsh chemistry performed during its normal function but also with requirements of the enzyme while it is undergoing assembly and repair. Key aspects of PSII reaction centre evolution are also addressed. This article is part of a Special Issue entitled: Photosystem II.
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Affiliation(s)
- Tanai Cardona
- Institut de Biologie et Technologies de Saclay, URA 2096 CNRS, CEA Saclay, 91191 Gif-sur-Yvette, France
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44
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Cardol P, Forti G, Finazzi G. Regulation of electron transport in microalgae. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2010; 1807:912-8. [PMID: 21167125 DOI: 10.1016/j.bbabio.2010.12.004] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2010] [Revised: 12/03/2010] [Accepted: 12/04/2010] [Indexed: 01/23/2023]
Abstract
Unicellular algae are characterized by an extreme flexibility with respect to their responses to environmental constraints. This flexibility probably explains why microalgae show a very high biomass yield, constitute one of the major contributors to primary productivity in the oceans and are considered a promising choice for biotechnological applications. Flexibility results from a combination of several factors including fast changes in the light-harvesting apparatus and a strong interaction between different metabolic processes (e.g. respiration and photosynthesis), which all take place within the same cell. Microalgae are also capable of modifying their photosynthetic electron flow capacity, by changing its maximum rate and/or by diverting photogenerated electrons towards different sinks depending on their growth status. In this review, we will focus on the occurrence and regulation of alternative electron flows in unicellular algae and compare data obtained in these systems with those available in vascular plants. This article is part of a Special Issue entitled: Regulation of Electron Transport in Chloroplasts.
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Affiliation(s)
- Pierre Cardol
- Laboratoire de Génétique des Microorganismes, Institut de Botanique, Université de Liège, 27 bld du rectorat, B-4000 Liège, Belgium
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Membrane potential is involved in regulation of photosynthetic reactions in the marine diatom Thalassiosira weissflogii. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2010; 102:169-73. [PMID: 21131210 DOI: 10.1016/j.jphotobiol.2010.11.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2010] [Revised: 11/10/2010] [Accepted: 11/11/2010] [Indexed: 10/18/2022]
Abstract
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. Moreover, valinomycin enhanced ΔpH-dependent non-photochemical fluorescence quenching following the OJIP rise. In the presence of valinomycin, the transthylakoid membrane potential was significantly inhibited as evaluated by measurements of the delayed light emission. The results suggest a membrane potential control of the fluorescence yield in T. weissflogii. Possible mechanisms underlying the observed effects of uncouplers are discussed.
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46
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Ohad I, Raanan H, Keren N, Tchernov D, Kaplan A. Light-induced changes within photosystem II protects Microcoleus sp. in biological desert sand crusts against excess light. PLoS One 2010; 5:e11000. [PMID: 20544016 PMCID: PMC2882322 DOI: 10.1371/journal.pone.0011000] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2010] [Accepted: 05/16/2010] [Indexed: 12/16/2022] Open
Abstract
The filamentous cyanobacterium Microcoleus vaginatus, a major primary producer in desert biological sand crusts, is exposed to frequent hydration (by early morning dew) followed by desiccation during potentially damaging excess light conditions. Nevertheless, its photosynthetic machinery is hardly affected by high light, unlike “model” organisms whereby light-induced oxidative stress leads to photoinactivation of the oxygen-evolving photosystem II (PSII). Field experiments showed a dramatic decline in the fluorescence yield with rising light intensity in both drying and artificially maintained wet plots. Laboratory experiments showed that, contrary to “model” organisms, photosynthesis persists in Microcoleus sp. even at light intensities 2–3 times higher than required to saturate oxygen evolution. This is despite an extensive loss (85–90%) of variable fluorescence and thermoluminescence, representing radiative PSII charge recombination that promotes the generation of damaging singlet oxygen. Light induced loss of variable fluorescence is not inhibited by the electron transfer inhibitors 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), 2,5-dibromo-3-methyl-6-isopropylbenzoquinone (DBMIB), nor the uncoupler carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP), thus indicating that reduction of plastoquinone or O2, or lumen acidification essential for non-photochemical quenching (NPQ) are not involved. The rate of QA− re-oxidation in the presence of DCMU is enhanced with time and intensity of illumination. The difference in temperatures required for maximal thermoluminescence emissions from S2/QA− (Q band, 22°C) and S2,3/QB− (B band, 25°C) charge recombinations is considerably smaller in Microcoleus as compared to “model” photosynthetic organisms, thus indicating a significant alteration of the S2/QA− redox potential. We propose that enhancement of non-radiative charge recombination with rising light intensity may reduce harmful radiative recombination events thereby lowering 1O2 generation and oxidative photodamage under excess illumination. This effective photo-protective mechanism was apparently lost during the evolution from the ancestor cyanobacteria to the higher plant chloroplast.
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Affiliation(s)
- Itzhak Ohad
- Department of Biological Chemistry, The Hebrew University of Jerusalem, Jerusalem, Irael
| | - Hagai Raanan
- Department of Plant and Environmental Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Nir Keren
- Department of Plant and Environmental Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Dan Tchernov
- The Interuniversity Institute for Marine Sciences in Eilat, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Aaron Kaplan
- Department of Plant and Environmental Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
- * E-mail:
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47
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Eisenstadt D, Barkan E, Luz B, Kaplan A. Enrichment of oxygen heavy isotopes during photosynthesis in phytoplankton. PHOTOSYNTHESIS RESEARCH 2010; 103:97-103. [PMID: 20054712 DOI: 10.1007/s11120-009-9518-z] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2009] [Accepted: 12/16/2009] [Indexed: 05/28/2023]
Abstract
Some of the oxygen produced during oxygenic photosynthesis is consumed but little is known about the extent of the processes involved. We measured the (17)O/(16)O and (18)O/(16)O ratios in O(2) produced by certain marine and freshwater phytoplankton representing important groups of primary producers. When the cells were performing photosynthesis under very low dissolved oxygen concentrations (< 3 μM), we observed significant enrichment in both (18)O and (17)O with respect to the substrate water. The difference in δ(18)O between O(2) and water was about 4.5, 3, 5.5, and 7‱ in the diatom Phaeodactylum tricornutum, Nannochloropsis sp. (Eustigmatophyceae), the coccolithophore Emiliania huxleyi and the green alga Chlamydomonas reinhardtii, respectively. The difference in δ(17)O was about 0.52 that of δ(18)O. As explained, the observed enrichments most probably stem from considerable oxygen consumption during photosynthesis even when major O(2)-consuming reactions such as photorespiration were minimized. These enrichments increased linearly with rising O(2) levels but with different δ(17)O/δ(18)O slopes for the various organisms, suggesting engagements of different O(2)-consuming reactions with rising O(2) levels. Consumption of O(2) may be important for energy dissipation during photosynthesis. The isotope enrichment observed here, not accounted for in earlier assessments, closes an important gap in our understanding of the difference between the isotopic compositions of atmospheric oxygen and that of seawater, i.e., the Dole effect.
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Affiliation(s)
- Doron Eisenstadt
- Department of Plant and Environmental Sciences, Hebrew University of Jerusalem, Israel
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Ducruet JM, Vass I. Thermoluminescence: experimental. PHOTOSYNTHESIS RESEARCH 2009; 101:195-204. [PMID: 19551489 DOI: 10.1007/s11120-009-9436-0] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2008] [Accepted: 05/13/2009] [Indexed: 05/24/2023]
Abstract
Thermoluminesence measurements are useful for the study of Photosystem II electron transport in intact leaves, in algal and cyanobacterial cells, as well as in isolated membrane complexes. Here an overview of the experimental approaches is provided. In the present review, instruments and the experimental procedures for measuring thermoluminescence emission from photosynthetic systems of various origins are summarized and discussed. Major pitfalls frequently encountered in measurements with isolated membranes, suspensions of intact organisms or solid leaf samples are highlighted. Analytical and numeric methods for the analysis of measured thermoluminescence curves are also discussed.
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Affiliation(s)
- Jean-Marc Ducruet
- Groupe de Biospectroscopie Végétale, Ecologie Systématique Evolution, Université Paris-Sud-Orsay & Institut National Recherche Agronomique, Orsay, France.
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Langner U, Jakob T, Stehfest K, Wilhelm C. An energy balance from absorbed photons to new biomass for Chlamydomonas reinhardtii and Chlamydomonas acidophila under neutral and extremely acidic growth conditions. PLANT, CELL & ENVIRONMENT 2009; 32:250-258. [PMID: 19054351 DOI: 10.1111/j.1365-3040.2008.01917.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Chlamydomonas is one of the most well-studied photosynthetic organisms that had important biotechnological potential for future bioproductions of biofuels. However, an energy balance from incident photons to the energy stored in the new biomass is still lacking. In this study, we applied a recently developed system to measure the energy balance for steady state growth of Chlamydomonas reinhardtii grown at pH 6.5, and C. acidophila that was grown at pH 6.5 and 2.6. Energy use efficiency was quantified on the basis of light absorption, photosynthetic quantum yield, photosynthetic and respiratory quotient, and electron partitioning into proteins, carbohydrates and lipids. The results showed that lower growth rates of C. acidophila under both pH conditions were not caused by the differences in the photosynthetic quantum yield or in alternative electron cycling, but rather by differences in the efficiency of light absorption and increased dark respiration. Analysis of the macromolecular composition of the cells during the light phase showed that C. acidophila uses biosynthetic electrons preferentially for carbohydrate synthesis but not for synthesis of lipids. This led to a strong diurnal cycle of the C/N ratio and could explain the higher dark respiration of C. acidophila compared with C. reinhardtii.
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Affiliation(s)
- Uwe Langner
- University of Leipzig, Institute of Biology I, Department of Plant Physiology, Leipzig, Germany
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Ivanov AG, Sane PV, Hurry V, Oquist G, Huner NPA. Photosystem II reaction centre quenching: mechanisms and physiological role. PHOTOSYNTHESIS RESEARCH 2008; 98:565-74. [PMID: 18821028 DOI: 10.1007/s11120-008-9365-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2008] [Accepted: 09/01/2008] [Indexed: 05/03/2023]
Abstract
Dissipation of excess absorbed light energy in eukaryotic photoautotrophs through zeaxanthin- and DeltapH-dependent photosystem II antenna quenching is considered the major mechanism for non-photochemical quenching and photoprotection. However, there is mounting evidence of a zeaxanthin-independent pathway for dissipation of excess light energy based within the PSII reaction centre that may also play a significant role in photoprotection. We summarize recent reports which indicate that this enigma can be explained, in part, by the fact that PSII reaction centres can be reversibly interconverted from photochemical energy transducers that convert light into ATP and NADPH to efficient, non-photochemical energy quenchers that protect the photosynthetic apparatus from photodamage. In our opinion, reaction centre quenching complements photoprotection through antenna quenching, and dynamic regulation of photosystem II reaction centre represents a general response to any environmental condition that predisposes the accumulation of reduced Q(A) in the photosystem II reaction centres of prokaryotic and eukaryotic photoautotrophs. Since the evolution of reaction centres preceded the evolution of light harvesting systems, reaction centre quenching may represent the oldest photoprotective mechanism.
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Affiliation(s)
- Alexander G Ivanov
- Department of Biology and The Biotron, University of Western Ontario, London, ON, Canada
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