Anthony Larkum

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.

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

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.

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...

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...

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

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.

ABSTRACT In Some Cyanobacteria, Poor Nutrient Conditions Induce A Reduction Of The Phycobilisome Light-Harvesting System And An Up-Regulation Of A Chlorophyll Antenna Protein, Isia, Which Can Form An 18-Mer Ring Around Photosystem I (Psi) Trimers. We Have Used The Recent High-Resolution Structure Of Photosystem Ii (Psii) To Obtain A New Model Of The Molecular Structure Of Isia, Which Evolved From Cp43. This Model Was Further Refined By Analysis Of Sequence Variation Among Cp43, Isia, And The Nterminal Part Of Psaa, To Produce A Model In Which There Are 16 Chlorophylls (Chls) Per Isia Subunit, Two More Than Previously Predicted. The Structure Of The Isia-Ps I Supercomplex Was Then Examined By Comparing The Potential Of Excitation Transfer, Which Is Done By Optimizing The Chl-Chl Distances.

Just over three years after the arrival of William Darwin Fox in Cambridge, another young man of nineteen arrived, in early 1828, who was destined to cause one of the biggest upheavals of the Nineteenth Century. Charles Darwin did not come directly from school as Fox did; he had left Shrewsbury School at the age of sixteen and had joined

ABSTRACT Growth, photosynthesis and photosynthetic efficiency have been measured in two diatoms: the commonly studied Phaeodactylum tricornutum and the sand diatom Amphora coffeaeformis. Both diatoms were grown under very high light and under low light (40 µmol.m−2.s−1). Photosynthesis was measured as oxygen yield and as electron transport rate. The ratios of photons absorbed by photosystem II to O2 evolved (quantum number), based on chlorophyll a (Θ*) and on surface area (Θ) for P. tricornutum and A. coffeaeformis under low light were between 5 and 6 and 9 and 11, respectively, and under high light were between 16 and 18 and 14 and 17, respectively. P vs E and ETR vs E curves were measured and from the oxygen yield results only a small amount of photoinhibition was observed. In A. coffeaeformis strong non-photochemical quenching was observed. The results show that diatoms exhibit flexible photosynthetic systems and under optimal conditions are very efficient.

... Anthony William Derek Larkum School of Biological Sciences, University of Sydney, NSW 2006, Australia (e-mail: alark@mail.usyd.edu.au; fax ... This work led to several books, the most famous of which was 'Klima und Boden in Ihrer Wirkung auf dass Pflanzenleben' ['Climate and ...

The “Voyage of the Beagle” is now as iconic an event in the life of Charles Darwin, as it is in the history of science. However, this is only with the hindsight of history and one should not forget the fact that there was a previous voyage and many subsequent voyages of this surveying ship of the British Navy, right

Several species of marine benthic algae, four species of phytoplankton and two species of seagrass have been subjected to ultraviolet B irradiation for varying lengths of time and the effects on respiration, photosynthesis and fluorescence rise kinetics studied. No effect on respiration was found. Photosynthesis was inhibited to a variable degree in all groups of plants after irradiation over periods of up to 1 h and variable fluorescence was also inhibited in a similar way. The most sensitive plants were phytoplankton and deep-water benthic algae. Intertidal benthic algae were the least sensitive to UV-B irradiation and this may be related to adaptation, through the accumulation of UV-B screening compounds, to high light/high UV-B levels. Inhibition of variable fluorescence (Fv) of the fluorescence rise curve was a fast and sensitive indicator of UV-B damage. Two plants studied, a brown alga and a seagrass, showed very poor recovery of Fv over a period of 32 h.

Flash-induced absorbance measurements at 830 nm on both nanosecond and microsecond timescales have been used to characterise the effect of ultraviolet light on Photosystem II core particles. A combination of UV-A and UV-B, closely simulating the spectrum of sunlight below 350 nm, was found to have a primary effect on the donor side of P680. Repetitive measurements indicated reductions in the nanosecond components of the absorbance decay with a concomitant appearance and increase in the amplitude of a component with a 10 μs time constant attributed to slow reduction of P680(+) by Tyrz when the function of the oxygen evolving complex is inhibited. Single-flash measurements show that the nanosecond components have amplitudes which vary with S-state. Increasing UV irradiation inhibited the amplitude of these components without changing their S-state dependence. In addition, UV irradiation resulted in a reduction in the total amplitude, with no change in the proportion of the 10 μs contribution.

... Mar. Biol. Ecol., Vol. 68, pp. 257-276. KENNELLY, S. & AWD LARKUM, 1984. A preliminary study of temporal variation in the colonization of subtidal algae in an Eddonia radiata community. Aquat. Bot., Vol. 17, pp. ... Trans. R. Soc. Afr., Vol. 44, pp. 27-41. NOVACZEK, I., 1980. ...