Publications by authors named "Charles Barry Osmond"

5 Publications

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

Photosynth Res 2021 Jul 28. Epub 2021 Jul 28.

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
July 2021

Inhibition of non-photochemical quenching increases functional absorption cross-section of photosystem II as excitation from closed reaction centres is transferred to open centres, facilitating earlier light saturation of photosynthetic electron transport.

Funct Plant Biol 2021 Mar 12. Epub 2021 Mar 12.

Induction of non-photochemical quenching (NPQ) of chlorophyll fluorescence in leaves affords photoprotection to the photosynthetic apparatus when, for whatever reason, photon capture in the antennae of photosystems exceeds their capacity to utilise this excitation in photochemistry and ultimately in CO2 assimilation. Here we augment traditional monitoring of NPQ using the fast time resolution, remote and relatively non-intrusive light induced fluorescence transient (LIFT) technique (Kolber et al. 2005; Osmond et al. 2017) that allows direct measurement of functional (σ'PSII) and optical cross-sections (a'PSII) of PSII in situ, and calculates the half saturation light intensity for ETR (Ek). These parameters are obtained from the saturation and relaxation phases of fluorescence transients elicited by a sequence of 270, high intensity 1 μs flashlets at controlled time intervals over a period of 30 ms in the QA flash at intervals of a few seconds. We report that although σ'PSII undergoes large transient increases after transfer from dark to strong white light (WL) it declines little in steady-state as NPQ is induced in shade- and sun-grown spinach and Arabidopsis genotypes Col, OEpsbs, pgr5bkg, stn7 and stn7/8. In contrast, σ'PSII increases by ~30% when induction of NPQ in spinach is inhibited by dithiothreitol and by inhibition of NPQ in Arabidopsis npq1, npq4 and pgr5. We propose this increase in σ'PSII arises as some excitation from closed PSII reaction centres is transferred to open centres when excitation partitioning to photochemistry (YII) and NPQ (YNP) declines, and is indicated by an increased excitation dissipation from closed PSII centres (YNO, including fluorescence emission). Although Ek increases following dissipation of excitation as heat when NPQ is engaged, it declines when NPQ is inhibited. Evidently photochemistry becomes more easily light saturated when excitation is transferred from closed RCIIs to open centres with larger σ'PSII. The NPQ mutant pgr5 is an exception; Ek increases markedly in strong light as electron transport QA → PQ and PQ → PSI accelerate and the PQ pool becomes strongly reduced. These novel in situ observations are discussed in the context of contemporary evidence for functional and structural changes in the photosynthetic apparatus during induction of NPQ.
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http://dx.doi.org/10.1071/FP20347DOI Listing
March 2021

Remembering Joan (Jan) Mary Anderson (1932-2015).

Photosynth Res 2016 Aug;129(2):129-46

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

Joan Mary Anderson, known to most people as Jan, was born on May 12, 1932 in Dunedin, New Zealand. She died on August 28, 2015 in Canberra, Australia. To celebrate her life, we present here a brief biography, some comments on her discoveries in photosynthesis during a career spanning more than half a century, and reminiscences from family and friends. We remember this wonderful person who had an unflagging curiosity, creative ability to think laterally, enthusiasm, passion, generosity and love of color and culture.
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http://dx.doi.org/10.1007/s11120-016-0287-1DOI Listing
August 2016

Lutein from deepoxidation of lutein epoxide replaces zeaxanthin to sustain an enhanced capacity for nonphotochemical chlorophyll fluorescence quenching in avocado shade leaves in the dark.

Plant Physiol 2011 May 22;156(1):393-403. Epub 2011 Mar 22.

Plant Sciences Division, Research School of Biology, Australian National University, Canberra, Australian Capital Territory 0200, Australia.

Leaves of avocado (Persea americana) that develop and persist in deep shade canopies have very low rates of photosynthesis but contain high concentrations of lutein epoxide (Lx) that are partially deepoxidized to lutein (L) after 1 h of exposure to 120 to 350 μmol photons m(-2) s(-1), increasing the total L pool by 5% to 10% (ΔL). Deepoxidation of Lx to L was near stoichiometric and similar in kinetics to deepoxidation of violaxanthin (V) to antheraxanthin (A) and zeaxanthin (Z). Although the V pool was restored by epoxidation of A and Z overnight, the Lx pool was not. Depending on leaf age and pretreatment, the pool of ΔL persisted for up to 72 h in the dark. Metabolism of ΔL did not involve epoxidation to Lx. These contrasting kinetics enabled us to differentiate three states of the capacity for nonphotochemical chlorophyll fluorescence quenching (NPQ) in attached and detached leaves: ΔpH dependent (NPQ(ΔpH)) before deepoxidation; after deepoxidation in the presence of ΔL, A, and Z (NPQ(ΔLAZ)); and after epoxidation of A+Z but with residual ΔL (NPQ(ΔL)). The capacity of both NPQ(ΔLAZ) and NPQ(ΔL) was similar and 45% larger than NPQ(ΔpH), but dark relaxation of NPQ(ΔLAZ) was slower. The enhanced capacity for NPQ was lost after metabolism of ΔL. The near equivalence of NPQ(ΔLAZ) and NPQ(ΔL) provides compelling evidence that the small dynamic pool ΔL replaces A+Z in avocado to "lock in" enhanced NPQ. The results are discussed in relation to data obtained with other Lx-rich species and in mutants of Arabidopsis (Arabidopsis thaliana) with increased L pools.
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http://dx.doi.org/10.1104/pp.111.173369DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3091066PMC
May 2011

Steady-state chlorophyll fluorescence (Fs) measurements as a tool to follow variations of net CO2 assimilation and stomatal conductance during water-stress in C3 plants.

Physiol Plant 2002 Feb;114(2):231-240

Laboratori de Fisiologia Vegetal, Departament de Biologia, Universitat de les Illes Balears-Institut Mediterrani d'Estudis Avançats (UIB-CSIC). Carretera de Valldemossa Km. 7.5, E-07071 Palma de Mallorca. Balears, Spain Laboratoire pour l'Utilization du Rayonnement Electromagnétique (LURE), Centre Universitaire Paris-Sud, B.P. 34; F-91898 Orsay Cedex, France Research School of Biological Sciences, Institute of Advanced Studies, Australian National University, Box 475, Canberra, ACT 2601, Australia.

Water stress experiments were performed with grapevines (Vitis vinifera L.) and other C3 plants in the field, in potted plants in the laboratory, and with detached leaves. It was found that, in all cases, the ratio of steady state chlorophyll fluorescence (Fs) normalized to dark-adapted intrinsic fluorescence (Fo) inversely correlated with non-photochemical quenching (NPQ). Also, at high irradiance, the ratio Fs/Fo was positively correlated with CO2 assimilation in air, with electron transport rate calculated from fluorescence, and with stomatal conductance, but no clear correlation was observed with qP. The significance of these relationships is discussed. The ratio Fs/Fo, measured with a portable instrument (PAM-2000) or with a remote sensing FIPAM system, provides a good method for the early detection of water stress, and may become a useful guide to irrigation requirements.
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http://dx.doi.org/10.1034/j.1399-3054.2002.1140209.xDOI Listing
February 2002
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