Publications by authors named "Duncan Fitzpatrick"

7 Publications

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Wah Soon Chow, a teacher, a friend and a colleague.

Photosynth Res 2021 Aug;149(1-2):253-258

Climate Change Cluster (C3), University of Technology Sydney, Sydney, NSW, 2007, Australia.

To finish this special issue, some friends, colleagues and students of Prof. Chow (Emeritus Professor, the Research School of Biology, the Australian National University) have written small tributes to acknowledge not only his eminent career but to describe his wonderful personality.
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http://dx.doi.org/10.1007/s11120-021-00864-wDOI Listing
August 2021

Upregulation of bundle sheath electron transport capacity under limiting light in C Setaria viridis.

Plant J 2021 Jun 7;106(5):1443-1454. Epub 2021 May 7.

Australian Research Council Centre of Excellence for Translational Photosynthesis, Division of Plant Science, Research School of Biology, The Australian National University, Acton, Australian Capital Territory, 2601, Australia.

C photosynthesis is a biochemical pathway that operates across mesophyll and bundle sheath (BS) cells to increase CO concentration at the site of CO fixation. C plants benefit from high irradiance but their efficiency decreases under shade, causing a loss of productivity in crop canopies. We investigated shade acclimation responses of Setaria viridis, a model monocot of NADP-dependent malic enzyme subtype, focussing on cell-specific electron transport capacity. Plants grown under low light (LL) maintained CO assimilation rates similar to high light plants but had an increased chlorophyll and light-harvesting-protein content, predominantly in BS cells. Photosystem II (PSII) protein abundance, oxygen-evolving activity and the PSII/PSI ratio were enhanced in LL BS cells, indicating a higher capacity for linear electron flow. Abundances of PSI, ATP synthase, Cytochrome b f and the chloroplast NAD(P)H dehydrogenase complex, which constitute the BS cyclic electron flow machinery, were also increased in LL plants. A decline in PEP carboxylase activity in mesophyll cells and a consequent shortage of reducing power in BS chloroplasts were associated with a more oxidised plastoquinone pool in LL plants and the formation of PSII - light-harvesting complex II supercomplexes with an increased oxygen evolution rate. Our results suggest that the supramolecular composition of PSII in BS cells is adjusted according to the redox state of the plastoquinone pool. This discovery contributes to the understanding of the acclimation of PSII activity in C plants and will support the development of strategies for crop improvement, including the engineering of C photosynthesis into C plants.
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http://dx.doi.org/10.1111/tpj.15247DOI Listing
June 2021

Dissecting the interaction of photosynthetic electron transfer with mitochondrial signalling and hypoxic response in the Arabidopsis mutant.

Philos Trans R Soc Lond B Biol Sci 2020 06 4;375(1801):20190413. Epub 2020 May 4.

Organismal and Evolutionary Biology Research Programme, Faculty of Biological and Environmental Sciences, University of Helsinki, FI-00014 Helsinki, Finland.

The Arabidopsis mutant is tolerant to methyl viologen (MV). MV enhances the Mehler reaction, i.e. electron transfer from Photosystem I (PSI) to O, generating reactive oxygen species (ROS) in the chloroplast. To study the MV tolerance of , we first addressed chloroplast thiol redox enzymes potentially implicated in ROS scavenging. NADPH-thioredoxin oxidoreductase type C (NTRC) was more reduced in . NTRC contributed to the photosynthetic and metabolic phenotypes of , but did not determine its MV tolerance. We next tested for alterations in the Mehler reaction. In , but not in the wild type, the PSI-to-MV electron transfer was abolished by hypoxic atmosphere. A characteristic feature of is constitutive expression of mitochondrial dysfunction stimulon (MDS) genes that affect mitochondrial respiration. Similarly to , in other MDS-overexpressing plants hypoxia also inhibited the PSI-to-MV electron transfer. One possible explanation is that the MDS gene products may affect the Mehler reaction by altering the availability of O. In green tissues, this putative effect is masked by photosynthetic O evolution. However, O evolution was rapidly suppressed in MV-treated plants. Transcriptomic meta-analysis indicated that MDS gene expression is linked to hypoxic response not only under MV, but also in standard growth conditions. This article is part of the theme issue 'Retrograde signalling from endosymbiotic organelles'.
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http://dx.doi.org/10.1098/rstb.2019.0413DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7209945PMC
June 2020

A Commonly Used Photosynthetic Inhibitor Fails to Block Electron Flow to Photosystem I in Intact Systems.

Front Plant Sci 2020 15;11:382. Epub 2020 Apr 15.

Molecular Plant Biology Unit, Department of Biochemistry, University of Turku, Turku, Finland.

In plant science, 2,4-dinitrophenylether of iodonitrothymol (DNP-INT) is frequently used as an alternative to 2,5-dibromo-6-isopropyl-3-methyl-1,4-benzoquinone (DBMIB) to examine the capacity of plastoquinol and semiquinone to reduce O. DNP-INT is considered to be an effective inhibitor of the photosynthetic electron transfer chain (PETC) through its binding at the Q site of Cyt-. The binding and action of DNP-INT has been previously characterized spectroscopically in purified Cyt- complex reconstituted with Plastocyanin, PSII membranes and plastoquinone, as well as in isolated thylakoids based on its property to block MV-mediated O consumption. Contrary to the conclusions obtained from these experiments, we observed clear reduction of P700 in samples incubated with DNP-INT during our recent investigation into the sites of oxygen consumption in isolated thylakoids. Therefore, we carried out an extensive investigation of DNP-INT's chemical efficacy in isolated thylakoids and intact leaves. This included examination of its capacity to block the PETC before PSI, and therefore its inhibition of CO fixation. P700 redox kinetics were measured using Dual-PAM whilst Membrane Inlet Mass Spectrometry (MIMS) was used for simultaneous determination of the rates of O evolution and O consumption in isolated thylakoids and CO fixation in intact leaves, using two stable isotopes of oxygen (O, O) and CO (C, C), respectively. Based on these investigations we confirmed that DNP-INT is unable to completely block the PETC and CO fixation, therefore its use may produce artifacts if applied to isolated thylakoids or intact cells, especially when determining the locations of reactive oxygen species formation in the photosynthetic apparatus.
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http://dx.doi.org/10.3389/fpls.2020.00382DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7174583PMC
April 2020

Cytochrome Decreases Photosynthesis under Photomixotrophy in sp. PCC 6803.

Plant Physiol 2020 06 21;183(2):700-716. Epub 2020 Apr 21.

Laboratory of Molecular Plant Biology, Department of Biochemistry, University of Turku, Turku FI-20014, Finland

Photomixotrophy is a metabolic state that enables photosynthetic microorganisms to simultaneously perform photosynthesis and metabolism of imported organic carbon substrates. This process is complicated in cyanobacteria, since many, including sp. PCC 6803, conduct photosynthesis and respiration in an interlinked thylakoid membrane electron transport chain. Under photomixotrophy, the cell must therefore tightly regulate electron fluxes from photosynthetic and respiratory complexes. In this study, we demonstrate, via characterization of photosynthetic apparatus and the proteome, that photomixotrophic growth results in a gradual inhibition of Q reoxidation in wild-type , which largely decreases photosynthesis over 3 d of growth. This process is circumvented by deleting the gene encoding cytochrome (CytM), a cryptic -type heme protein widespread in cyanobacteria. The ΔCytM strain maintained active photosynthesis over the 3-d period, demonstrated by high photosynthetic O and CO fluxes and effective yields of PSI and PSII. Overall, this resulted in a higher growth rate compared to that of the wild type, which was maintained by accumulation of proteins involved in phosphate and metal uptake, and cofactor biosynthetic enzymes. While the exact role of CytM has not been determined, a mutant deficient in the thylakoid-localized respiratory terminal oxidases and CytM (ΔCox/Cyd/CytM) displayed a phenotype similar to that of ΔCytM under photomixotrophy. This, in combination with other physiological data, and in contrast to a previous hypothesis, suggests that CytM does not transfer electrons to these complexes. In summary, our data suggest that CytM may have a regulatory role in photomixotrophy by modulating the photosynthetic capacity of cells.
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http://dx.doi.org/10.1104/pp.20.00284DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7271781PMC
June 2020

Redirecting photosynthetic electron flux in the cyanobacterium Synechocystis sp. PCC 6803 by the deletion of flavodiiron protein Flv3.

Microb Cell Fact 2019 Nov 5;18(1):189. Epub 2019 Nov 5.

Molecular Plant Biology, Department of Biochemistry, University of Turku, 20014, Turun Yliopisto, Finland.

Background: Oxygen-evolving photoautotrophic organisms, like cyanobacteria, protect their photosynthetic machinery by a number of regulatory mechanisms, including alternative electron transfer pathways. Despite the importance in modulating the electron flux distribution between the photosystems, alternative electron transfer routes may compete with the solar-driven production of CO-derived target chemicals in biotechnological systems under development. This work focused on engineered cyanobacterial Synechocystis sp. PCC 6803 strains, to explore possibilities to rescue excited electrons that would normally be lost to molecular oxygen by an alternative acceptor flavodiiron protein Flv1/3-an enzyme that is natively associated with transfer of electrons from PSI to O, as part of an acclimation strategy towards varying environmental conditions.

Results: The effects of Flv1/3 inactivation by flv3 deletion were studied in respect to three alternative end-products, sucrose, polyhydroxybutyrate and glycogen, while the photosynthetic gas fluxes were monitored by Membrane Inlet Mass Spectrometry (MIMS) to acquire information on cellular carbon uptake, and the production and consumption of O. The results demonstrated that a significant proportion of the excited electrons derived from photosynthetic water cleavage was lost to molecular oxygen via Flv1/3 in cells grown under high CO, especially under high light intensities. In flv3 deletion strains these electrons could be re-routed to increase the relative metabolic flux towards the monitored target products, but the carbon distribution and the overall efficiency were determined by the light conditions and the genetic composition of the respective pathways. At the same time, the total photosynthetic capacity of the Δflv3 strains was systematically reduced, and accompanied by upregulation of oxidative glycolytic metabolism in respect to controls with the native Flv1/3 background.

Conclusions: The observed metabolic changes and respective production profiles were proposedly linked with the lack of Flv1/3-mediated electron transfer, and the associated decrease in the intracellular ATP/NADPH ratio, which is bound to affect the metabolic carbon partitioning in the flv3-deficient cells. While the deletion of flv3 could offer a strategy for enhancing the photosynthetic production of desired chemicals in cyanobacteria under specified conditions, the engineered target pathways have to be carefully selected to align with the intracellular redox balance of the cells.
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http://dx.doi.org/10.1186/s12934-019-1238-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6833302PMC
November 2019

Obstacles in the quantification of the cyclic electron flux around Photosystem I in leaves of C3 plants.

Photosynth Res 2016 Sep 4;129(3):239-51. Epub 2016 Feb 4.

Division of Plant Sciences, Research School of Biology, The Australian National University, 46 Sullivans Creek Road, Acton, ACT, 2601, Australia.

Sixty years ago Arnon and co-workers discovered photophosphorylation driven by a cyclic electron flux (CEF) around Photosystem I. Since then understanding the physiological roles and the regulation of CEF has progressed, mainly via genetic approaches. One basic problem remains, however: quantifying CEF in the absence of a net product. Quantification of CEF under physiological conditions is a crucial prerequisite for investigating the physiological roles of CEF. Here we summarize current progress in methods of CEF quantification in leaves and, in some cases, in isolated thylakoids, of C3 plants. Evidently, all present methods have their own shortcomings. We conclude that to quantify CEF in vivo, the best way currently is to measure the electron flux through PS I (ETR1) and that through PS II and PS I in series (ETR2) for the whole leaf tissue under identical conditions. The difference between ETR1 and ETR2 is an upper estimate of CEF, mainly consisting, in C3 plants, of a major PGR5-PGRL1-dependent CEF component and a minor chloroplast NDH-dependent component, where PGR5 stands for Proton Gradient Regulation 5 protein, PGRL1 for PGR5-like photosynthesis phenotype 1, and NDH for Chloroplast NADH dehydrogenase-like complex. These two CEF components can be separated by the use of antimycin A to inhibit the former (major) component. Membrane inlet mass spectrometry utilizing stable oxygen isotopes provides a reliable estimation of ETR2, whilst ETR1 can be estimated from a method based on the photochemical yield of PS I, Y(I). However, some issues for the recommended method remain unresolved.
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http://dx.doi.org/10.1007/s11120-016-0223-4DOI Listing
September 2016
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