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Papers by Anthony Larkum

SEAGRASSES: …, Jan 1, 2006

Trends in Plant Science, 2015

Photosynthesis is one of the most important processes on our planet, providing food and oxygen fo... more Photosynthesis is one of the most important processes on our planet, providing food and oxygen for the majority of living organisms on Earth. Over the past 30 years scientists have made great strides in understanding the central photosynthetic process of oxygenic photosynthesis, whereby water is used to provide the hydrogen and reducing equivalents vital to CO2 reduction and sugar formation. A recent crystal structure at 1.9-1.95Å has made possible an unparalleled map of the structure of photosystem II (PSII) and particularly the manganese-calcium (Mn-Ca) cluster, which is responsible for splitting water. Here we review how knowledge of the water-splitting site provides important criteria for the design of artificial Mn-based water-oxidizing catalysts, allowing the development of clean and sustainable solar energy technologies.

Febs Letters, 2007

Electron paramagnetic resonance (EPR) spectroscopy reveals functional and structural similarities... more Electron paramagnetic resonance (EPR) spectroscopy reveals functional and structural similarities between the reaction centres of the chlorophyll d-binding photosystem I (PS I) and chlorophyll a-binding PS I. Continuous wave EPR spectrometry at 12K identifies iron–sulphur centres as terminal electron acceptors of chlorophyll d-binding PS I. A transient light-induced electron spin echo (ESE) signal indicates the presence of a quinone as

ChemSusChem, Jan 24, 2015

This study presents the first in-depth analysis of CO2 limitation on the biomass productivity of ... more This study presents the first in-depth analysis of CO2 limitation on the biomass productivity of the biofuel candidate marine microalga Nannochloropsis oculata. Net photosynthesis decreased by 60 % from 125 to 50 μmol O 2 L(-1) h(-1) over a 12 h light cycle as a direct result of carbon limitation. Continuous dissolved O2 and pH measurements were used to develop a detailed diurnal mechanism for the interaction between photosynthesis, gas exchange and carbonate chemistry in the photo-bioreactor. Gas exchange determined the degree of carbon limitation experienced by the algae. Carbon limitation was confirmed by delivering more CO2 , which increased net photosynthesis back to its steady-state maximum. This study highlights the importance of maintaining replete carbon concentrations in photo-bioreactors and other culturing facilities, either by constant pH operation or preferably by designing a feedback loop based on the dissolved O2 concentration.

Environmental microbiology, Jan 14, 2015

The cyanobacterium Prochloron didemni is primarily found in symbiotic relationships with various ... more The cyanobacterium Prochloron didemni is primarily found in symbiotic relationships with various marine hosts such as ascidians and sponges. Prochloron remains to be successfully cultivated outside of its host, which reflects a lack of knowledge of its unique ecophysiological requirements. We investigated the microenvironment and diversity of Prochloron inhabiting the upper, exposed surface of didemnid ascidians, providing the first insights into this microhabitat. The pH and O2 concentration in this Prochloron biofilm changes dynamically with irradiance, where photosynthetic activity measurements showed low light adaptation (Ek ∼80±7 μmol photons m(-2) s(-1) ) but high light tolerance. Surface Prochloron cells exhibited a different fine structure to Prochloron cells from cloacal cavities in other ascidians, the principle difference being a central area of many vacuoles dissected by single thylakoids in the surface Prochloron. Cyanobacterial 16S rDNA pyro-sequencing of the biofilm c...

Coral Reefs, 2014

Coral cell cultures made from reef-building scleractinian corals have the potential to aid in the... more Coral cell cultures made from reef-building scleractinian corals have the potential to aid in the pursuit of understanding of the cnidarian-dinoflagellate symbiosis. Various methods have previously been described for the production of cell cultures in vitro with a range of success and longevity. In this study, viable tissue spheroids containing host tissue and symbionts (coral explants) were grown from the tissues of Fungia granulosa. The cultured explants remained viable for over 2 months and showed morphological similarities in tissue structure and internal microenvironment to reef-building scleractinian corals. The photophysiology of the explants (1 week old) closely matched that of the parent coral F. granulosa. This study provides the first empirical basis for supporting the use of coral explants as laboratory models for studying coral symbioses. In particular, it highlights how these small, selfsustaining, skeleton-free models can be useful for a number of molecular, genetic and physiological analyses necessary for investigating host-symbiont interactions at the microscale.

Current Research in Photosynthesis, 1990

Advances in Botanical Research, 1983

Enigmatic Microorganisms and Life in Extreme Environments, 1999

Research in Photosynthesis, 1992

Photosynthesis research, 2001

The adverse effect of low intensity, small band UV-B irradiation (lambda = 305 +/- 5 nm, I = 300 ... more The adverse effect of low intensity, small band UV-B irradiation (lambda = 305 +/- 5 nm, I = 300 mW m(-2)) on PS II has been studied by comparative measurements of laser flash-induced changes of the absorption at 325 nm, DeltaA(325)(t), as an indicator of redox changes in Q(A), and of the relative fluorescence quantum yield, F(t)/F(o), in PS II membrane fragments. The properties of untreated control were compared with those of samples where the oxygen evolution rate under illumination with continuous saturating light was inhibited by up to 95%. The following results were obtained: a) the detectable initial amplitude (at a time resolution of 30 mus) of the 325 nm absorption changes, DeltaA(325), remained virtually invariant whereas the relaxation kinetics exhibit significant changes, b) the 300 mus kinetics of DeltaA(325) dominating the relaxation in UV-B treated samples was largely replaced by a 1.3 ms kinetics after addition of MnCl(2), c) the extent of the flash induced rise of th...

Advanced Topics in Science and Technology in China, 2013

Advances in Photosynthesis and Respiration, 2006

Photosynthesis evolved very early on the Earth, but after respiration, and probably after the met... more Photosynthesis evolved very early on the Earth, but after respiration, and probably after the metabolic processes for methanogenesis and sulfur oxidation. This occurred in ancestors of anoxygenic photosynthetic bacteria. An ancestral reaction center of Photosystem I and II (RCI/II) type of photosynthesis arose in which a five membrane-spanning helix (MSH) protein bound two molecules of chlorophyll (Chl)/bacteriochlorophyll (BChl) in a

Advances in Photosynthesis and Respiration, 2003

Advances in Photosynthesis and Respiration, 2003

Light harvesting in algae is very diverse and reflects the broad spectrum of organisms involved a... more Light harvesting in algae is very diverse and reflects the broad spectrum of organisms involved and their long history of evolution compared to higher plants. This chapter concentrates on the chlorophylls (Chls) and their binding proteins, as they are the major photosynthetic pigments. Three chlorophylls occur in the algae, Chl a, Chl b and Chl c, attached to light-harvesting proteins, mainly in the CAB/CAC family. In classical Cyanobacteria typical CAB/CAC proteins are not found and the only member of the Chl c family present is Mg divinyl-2,4- pheoporphyrin methyl ester (MgDVP). In Cyanobacteria the light-harvesting proteins are typically phycobiliproteins (under nitrogen sufficient conditions) and isiA proteins (under nitrogen limiting conditions). In prochlorophytes and Acaryochoris marina, which are Cyanobacteria, a prochlorophyte chlorophyll binding protein (pcb protein) binds Chl a and Chl b, and sometimes MgDVP, or Chl d. The binding of Chl in these proteins and in other antenna proteins is discussed. These proteins serve to optimize energy distribution to the two photosystems, with controls at several levels of organization. A major problem in all oxygenic photosynthetic organisms (Cyanobacteria, algae and higher plants) is the generation of oxygen free radicals, particularly by Photosystem II. This leads to photoinhibitory damage, which is partially offset by mechanisms which down- regulate photosynthesis, particularly Photosystem II, and dissipate incoming energy as heat. The xanthophyll cycle is found in all algae, with the possible exception of red algae and cryptophytes, and, by processes which are only partially known, diverts light energy to heat energy when switched on. Algae can control their uptake of light energy in a variety of ways: by physiological mechanisms and by regulation of transcription and translation of proteins. These responses can be to both light quality and light quantity. Algae show a wide range of rearrangements of the light harvesting apparatus in relation to the photosystems, known as state transitions, which alter the optical cross-sectional areas of PS I and PS II.

SEAGRASSES: …, Jan 1, 2006

Trends in Plant Science, 2015

Photosynthesis is one of the most important processes on our planet, providing food and oxygen fo... more Photosynthesis is one of the most important processes on our planet, providing food and oxygen for the majority of living organisms on Earth. Over the past 30 years scientists have made great strides in understanding the central photosynthetic process of oxygenic photosynthesis, whereby water is used to provide the hydrogen and reducing equivalents vital to CO2 reduction and sugar formation. A recent crystal structure at 1.9-1.95Å has made possible an unparalleled map of the structure of photosystem II (PSII) and particularly the manganese-calcium (Mn-Ca) cluster, which is responsible for splitting water. Here we review how knowledge of the water-splitting site provides important criteria for the design of artificial Mn-based water-oxidizing catalysts, allowing the development of clean and sustainable solar energy technologies.

Febs Letters, 2007

Electron paramagnetic resonance (EPR) spectroscopy reveals functional and structural similarities... more Electron paramagnetic resonance (EPR) spectroscopy reveals functional and structural similarities between the reaction centres of the chlorophyll d-binding photosystem I (PS I) and chlorophyll a-binding PS I. Continuous wave EPR spectrometry at 12K identifies iron–sulphur centres as terminal electron acceptors of chlorophyll d-binding PS I. A transient light-induced electron spin echo (ESE) signal indicates the presence of a quinone as

ChemSusChem, Jan 24, 2015

This study presents the first in-depth analysis of CO2 limitation on the biomass productivity of ... more This study presents the first in-depth analysis of CO2 limitation on the biomass productivity of the biofuel candidate marine microalga Nannochloropsis oculata. Net photosynthesis decreased by 60 % from 125 to 50 μmol O 2 L(-1) h(-1) over a 12 h light cycle as a direct result of carbon limitation. Continuous dissolved O2 and pH measurements were used to develop a detailed diurnal mechanism for the interaction between photosynthesis, gas exchange and carbonate chemistry in the photo-bioreactor. Gas exchange determined the degree of carbon limitation experienced by the algae. Carbon limitation was confirmed by delivering more CO2 , which increased net photosynthesis back to its steady-state maximum. This study highlights the importance of maintaining replete carbon concentrations in photo-bioreactors and other culturing facilities, either by constant pH operation or preferably by designing a feedback loop based on the dissolved O2 concentration.

Environmental microbiology, Jan 14, 2015

The cyanobacterium Prochloron didemni is primarily found in symbiotic relationships with various ... more The cyanobacterium Prochloron didemni is primarily found in symbiotic relationships with various marine hosts such as ascidians and sponges. Prochloron remains to be successfully cultivated outside of its host, which reflects a lack of knowledge of its unique ecophysiological requirements. We investigated the microenvironment and diversity of Prochloron inhabiting the upper, exposed surface of didemnid ascidians, providing the first insights into this microhabitat. The pH and O2 concentration in this Prochloron biofilm changes dynamically with irradiance, where photosynthetic activity measurements showed low light adaptation (Ek ∼80±7 μmol photons m(-2) s(-1) ) but high light tolerance. Surface Prochloron cells exhibited a different fine structure to Prochloron cells from cloacal cavities in other ascidians, the principle difference being a central area of many vacuoles dissected by single thylakoids in the surface Prochloron. Cyanobacterial 16S rDNA pyro-sequencing of the biofilm c...

Coral Reefs, 2014

Coral cell cultures made from reef-building scleractinian corals have the potential to aid in the... more Coral cell cultures made from reef-building scleractinian corals have the potential to aid in the pursuit of understanding of the cnidarian-dinoflagellate symbiosis. Various methods have previously been described for the production of cell cultures in vitro with a range of success and longevity. In this study, viable tissue spheroids containing host tissue and symbionts (coral explants) were grown from the tissues of Fungia granulosa. The cultured explants remained viable for over 2 months and showed morphological similarities in tissue structure and internal microenvironment to reef-building scleractinian corals. The photophysiology of the explants (1 week old) closely matched that of the parent coral F. granulosa. This study provides the first empirical basis for supporting the use of coral explants as laboratory models for studying coral symbioses. In particular, it highlights how these small, selfsustaining, skeleton-free models can be useful for a number of molecular, genetic and physiological analyses necessary for investigating host-symbiont interactions at the microscale.

Current Research in Photosynthesis, 1990

Advances in Botanical Research, 1983

Enigmatic Microorganisms and Life in Extreme Environments, 1999

Research in Photosynthesis, 1992

Photosynthesis research, 2001

The adverse effect of low intensity, small band UV-B irradiation (lambda = 305 +/- 5 nm, I = 300 ... more The adverse effect of low intensity, small band UV-B irradiation (lambda = 305 +/- 5 nm, I = 300 mW m(-2)) on PS II has been studied by comparative measurements of laser flash-induced changes of the absorption at 325 nm, DeltaA(325)(t), as an indicator of redox changes in Q(A), and of the relative fluorescence quantum yield, F(t)/F(o), in PS II membrane fragments. The properties of untreated control were compared with those of samples where the oxygen evolution rate under illumination with continuous saturating light was inhibited by up to 95%. The following results were obtained: a) the detectable initial amplitude (at a time resolution of 30 mus) of the 325 nm absorption changes, DeltaA(325), remained virtually invariant whereas the relaxation kinetics exhibit significant changes, b) the 300 mus kinetics of DeltaA(325) dominating the relaxation in UV-B treated samples was largely replaced by a 1.3 ms kinetics after addition of MnCl(2), c) the extent of the flash induced rise of th...

Advanced Topics in Science and Technology in China, 2013

Advances in Photosynthesis and Respiration, 2006

Photosynthesis evolved very early on the Earth, but after respiration, and probably after the met... more Photosynthesis evolved very early on the Earth, but after respiration, and probably after the metabolic processes for methanogenesis and sulfur oxidation. This occurred in ancestors of anoxygenic photosynthetic bacteria. An ancestral reaction center of Photosystem I and II (RCI/II) type of photosynthesis arose in which a five membrane-spanning helix (MSH) protein bound two molecules of chlorophyll (Chl)/bacteriochlorophyll (BChl) in a

Advances in Photosynthesis and Respiration, 2003

Advances in Photosynthesis and Respiration, 2003

Light harvesting in algae is very diverse and reflects the broad spectrum of organisms involved a... more Light harvesting in algae is very diverse and reflects the broad spectrum of organisms involved and their long history of evolution compared to higher plants. This chapter concentrates on the chlorophylls (Chls) and their binding proteins, as they are the major photosynthetic pigments. Three chlorophylls occur in the algae, Chl a, Chl b and Chl c, attached to light-harvesting proteins, mainly in the CAB/CAC family. In classical Cyanobacteria typical CAB/CAC proteins are not found and the only member of the Chl c family present is Mg divinyl-2,4- pheoporphyrin methyl ester (MgDVP). In Cyanobacteria the light-harvesting proteins are typically phycobiliproteins (under nitrogen sufficient conditions) and isiA proteins (under nitrogen limiting conditions). In prochlorophytes and Acaryochoris marina, which are Cyanobacteria, a prochlorophyte chlorophyll binding protein (pcb protein) binds Chl a and Chl b, and sometimes MgDVP, or Chl d. The binding of Chl in these proteins and in other antenna proteins is discussed. These proteins serve to optimize energy distribution to the two photosystems, with controls at several levels of organization. A major problem in all oxygenic photosynthetic organisms (Cyanobacteria, algae and higher plants) is the generation of oxygen free radicals, particularly by Photosystem II. This leads to photoinhibitory damage, which is partially offset by mechanisms which down- regulate photosynthesis, particularly Photosystem II, and dissipate incoming energy as heat. The xanthophyll cycle is found in all algae, with the possible exception of red algae and cryptophytes, and, by processes which are only partially known, diverts light energy to heat energy when switched on. Algae can control their uptake of light energy in a variety of ways: by physiological mechanisms and by regulation of transcription and translation of proteins. These responses can be to both light quality and light quantity. Algae show a wide range of rearrangements of the light harvesting apparatus in relation to the photosystems, known as state transitions, which alter the optical cross-sectional areas of PS I and PS II.

Schliep M, Quinnell R, Stranger R, Larkum AWD. 2013. Formyl group modification of chlorophyll a: ... more Schliep M, Quinnell R, Stranger R, Larkum AWD. 2013. Formyl group modification of chlorophyll a: a major evolutionary mechanism in oxygenic photosynthesis. Plant, Cell & Environment. 36: 3, 521–527. [Article first published online: 20 SEP 2012 DOI: 10.1111/pce.12000]

We discuss recent advances in chlorophyll research in the context of chlorophyll evolution and conclude that some derivations of the formyl side chain arrangement of the porphyrin ring from that of the Chl a macrocycle can extend the photosynthetic active radiation (PAR) of these molecules, e.g. Chl d and Chl f absorb light in the near infra-red region, up to ∼750 nm. Derivations such as this confer a selective advantage in particular niches and may, therefore, be beneficial for photosynthetic organisms thriving in light environments with particular light signatures, such as red- and near far red-light enriched niches. Modelling of formyl side chain substitutions of Chl a revealed yet unidentified but theoretically possible Chls with a distinct shift of light absorption properties when compared to Chl a.

The cyanobacterium Acaryochloris marina is an exceptional organism utilising chlorophyll d (Chl d... more The cyanobacterium Acaryochloris marina is an exceptional organism utilising chlorophyll d (Chl d) as its major photosynthetic pigment. Acaryochloris cells contain 90–99% Chl d with minor amounts of chlorophyll a and a chlorophyll c-like pigment. These unusual characteristics make it an excellent candidate to study various aspects of photosynthesis driven by Chl d. However, little is known about the pathway of Chl d biosynthesis. We specifically designed HPLC methods to analyse pigment compositions of Acaryochloris. This enabled us to detect intermediate products of the chlorophyll biosynthesis. We identified Mg-Protoporphyrin IX monomethyl ester (MgPMe) and Mg-2,4-divinyl pheoporphyrin (MgDVP) and the environmental factors influencing their concentration levels. HPLC-facilitated analysis of pigments from Acaryochloris cells cultured under various light quantities was performed; light stress conditions induced an increase in the ratio of MgDVP to Chl d. Pigment analysis of Acaryochloris cells grown under oxygen-stressed conditions demonstrated a decrease in MgDVP levels. We propose that the Chl d biosynthesis pathway favours an aerobic environment despite the fact that Acaryochloris cells can survive under anaerobic conditions.

FEBS letters, Jan 1, 2002

The major light-harvesting protein complex containing chlorophyll (Chl) d was isolated from Acary... more The major light-harvesting protein complex containing chlorophyll (Chl) d was isolated from Acaryochloris marina thylakoid membranes. Isolation was achieved by detergent solubilisation followed by separation on 6–40% sucrose gradients using ultracentrifugation. The best Chl d yield (70%) used 0.3% dodecyl maltoside, 0.15% octyl glucoside, 0.05% zwittergent 3-14 with the detergent:total Chl d ratio around 10:1 (w/w). Characterisation of the light-harvesting pigment protein complex (lhc) involved non-denaturing electrophoresis, SDS–PAGE, absorbance and fluorescence spectroscopy. The main polypeptide in the lhc was shown to be ca. 34 kDa and to contain Chl d and Chl a, indicating that the Acaryochloris lhc is similar to that of prochlorophytes. The Chl a level varied with the culture conditions, which is consistent with previous findings.