Fluorescence analysis during steady-state photosynthesis

Photosynthetic gas exchange of attached leaves has been measured under steady-state conditions at different light intensities and correlated with simultaneous measurements of chlorophyll fluorescence and oxidized P 700 (by absorbance changes at 820 nm). The data suggest that during light-saturated assimilation, photosystem II (PSII) photochemistry is mainly controlled by non-photochemical and non-radiative dissipation of excitation energy, rather than by accumulation of reduced acceptor, Q A , and this could be related to ‘high-energy quenching’ of fluorescence. The occurrence of oxidized P 700 at saturating light and low concentration of CO 2 suggests that in the steady state PSI photochemistry is controlled by a shortage of electron donation from the plastoquinone pool (photosynthetic control), rather than by excess electrons at the acceptor side. The significance of the oxidized form of P 700 as a ‘quencher’ of excitation energy is discussed. This control of photosystems I and II, both related to the proton gradient across the thylakoid membrane, may serve to match the potential rate of net photochemistry to the demand by the biochemical reactions. However, when light-saturated assimilation is not limited by CO 2 , PSI activity is controlled by accumulation of reduced electron acceptors, rather than by photosynthetic mechanisms. Photosynthetic control has been found to determine the redox state of the ferredoxin-thioredoxin system.

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Dissipative cooling induced by pulse perturbations

SciPost Physics ◽

10.21468/scipostphys.12.1.014 ◽

2022 ◽

Vol 12 (1) ◽

Author(s):

ANDREA NAVA ◽

Michele Fabrizio

Keyword(s):

Steady State ◽

Excitation Energy ◽

Ising Models ◽

High Energy ◽

Energy Sector ◽

Low Energy ◽

Quasi Steady State ◽

Pulse Perturbation ◽

Long Time ◽

Infinite Range

We investigate the dynamics brought on by an impulse perturbation in two infinite-range quantum Ising models coupled to each other and to a dissipative bath. We show that, if dissipation is faster the higher the excitation energy, the pulse perturbation cools down the low-energy sector of the system, at the expense of the high-energy one, eventually stabilising a transient symmetry-broken state at temperatures higher than the equilibrium critical one. Such non-thermal quasi-steady state may survive for quite a long time after the pulse, if the latter is properly tailored.

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Reduced substrate oxidation in postischemic myocardium: 13C and 31P NMR analyses

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1990.258.5.h1357 ◽

1990 ◽

Vol 258 (5) ◽

pp. H1357-H1365 ◽

Cited By ~ 7

Author(s):

E. D. Lewandowski ◽

D. L. Johnston

Keyword(s):

Steady State ◽

31P Nmr ◽

Tca Cycle ◽

High Energy ◽

Substrate Oxidation ◽

High Energy Phosphates ◽

Atp Content ◽

And Control ◽

13C And 31P Nmr ◽

Postischemic Myocardium

13C and 31P nuclear magnetic resonance (NMR) spectra were used to assess substrate oxidation and high-energy phosphates in postischemic (PI) isolated rabbit hearts. Phosphocreatine (PCr) increased in nonischemic controls on switching from glucose perfusion to either 2.5 mM [3-13C]pyruvate (120%, n = 7) or [2-13C]acetate (114%, n = 8, P less than 0.05). ATP content, oxygen consumption (MVO2), and hemodynamics (dP/dt) were not affected by substrate availability in control or PI hearts. dP/dt was 40-60% lower in PI hearts during reperfusion after 10 min ischemia. Hearts reperfused with either pyruvate (n = 11) or acetate (n = 8) regained preischemic PCr levels within 45 s. Steady-state ATP levels were 55-70% of preischemia with pyruvate and 52-60% with acetate. Percent maximum [4-13C]glutamate signal showed reduced conversion of pyruvate to glutamate via the tricarboxylic acid (TCA) cycle at 4-min reperfusion (PI = 24 +/- 4%, means +/- SE; Control = 48 +/- 4%). The increase in 13C signal from the C-4 position of glutamate was similar to control hearts within 10.5 min. The increase in [4-13C]glutamate signal from acetate was not different between PI and control hearts. The ratio of [2-13C]Glu:[4-13C]Glu, reflecting TCA cycle activity, was reduced in PI hearts with acetate for at least 10 min (Control = 0.76 +/- 0.03; PI = 0.51 +/- 0.09) until steady state was reached. Despite rapid recovery of oxidative phosphorylation, contractility remained impaired and substrate oxidation was significantly slowed in postischemic hearts.

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A radical departure from the ‘steady-state’ concept in cosmology

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1966.0043 ◽

1966 ◽

Vol 290 (1421) ◽

pp. 162-176 ◽

Cited By ~ 36

Keyword(s):

Steady State ◽

Cosmic Rays ◽

High Energy ◽

Expansion Rate ◽

Coupling Constant ◽

De Sitter ◽

Observable Universe ◽

State Expansion ◽

The Masses ◽

Creation Of Matter

The results in this paper are based on an entirely different choice of the undetermined coupling constant f which appears in the theory of creation of matter. Previously f was chosen to make the steady-state expansion rate coincident with the observed expansion rate. Now that we take a much larger value for f , the corresponding steady-state expansion rate is much greater than the observed value. We interpret this difference as showing that we live in a wide, possibly temporary, fluctuation from the steady-state situation. The expansion rate in such a fluctuation follows the Einstein-de Sitter relations. The natural scale set by the new steady-state corresponds to the masses of clusters of galaxies, we obtain 10 13 M0 instead of 10 23 M@ for the ‘observable universe’. It is suggested that elliptical galaxies were formed early in the development of a fluctuation. Our discussion of high energy phenomena leads to im m ediate explanations of the energy spectrum of cosmic rays, of the presence of e + in cosmic rays and of the rate of energy production associated with radio sources.

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The Effect of Halothane on the Steady-state Levels of High-energy Phosphates in the Neonatal Heart

Anesthesiology ◽

10.1097/00000542-198708000-00013 ◽

1987 ◽

Vol 67 (2) ◽

pp. 231-235 ◽

Cited By ~ 10

Author(s):

John J. McAuliffe ◽

Paul R. Hickey

Keyword(s):

Steady State ◽

High Energy ◽

High Energy Phosphates ◽

Neonatal Heart ◽

Steady State Levels

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Ultrafast charge transfer dynamics in 2D Covalent Organic Frameworks/Re-complex hybrid photocatalyst for CO2 reduction: hot electrons vs. cold electrons

10.21203/rs.3.rs-448398/v1 ◽

2021 ◽

Author(s):

Qinying Pan ◽

Mohamed Abdellah ◽

Yuehan Cao ◽

Yang Liu ◽

Weihua Lin ◽

...

Keyword(s):

Excited State ◽

Charge Transfer ◽

Excitation Energy ◽

Co2 Reduction ◽

Underlying Mechanism ◽

High Energy ◽

Hot Electrons ◽

Covalent Organic Frameworks ◽

Energy Excitation ◽

Energy Dependent

Abstract Rhenium(I)-carbonyl-diimine complexes are promising photocatalysts for CO2 reduction. Covalent organic frameworks (COFs) can be perfect sensitizers to enhance the reduction activities. Here we investigated the excited state dynamics of COF (TpBpy) with 2,2'-bipyridine incorporating Re(CO)5Cl (Re-TpBpy) to rationalize the underlying mechanism. The time-dependent DFT calculation first clarified excited state structure of the hybrid catalyst. The studies from transient visible and infrared spectroscopies revealed the excitation energy-dependent photo-induced charge transfer pathways in Re-TpBpy. Under low energy excitation, the electrons at the LUMO level are quickly injected from Bpy into ReI center (1–2 ps) followed by backward recombination (13 ps). Under high energy excitation, the hot-electrons are first injected into the higher unoccupied level of ReI center (1–2 ps) and then slowly relax back to the HOMO in COF (24 ps). There also remains long-lived free electrons in the COF moiety. This explained the excitation energy-dependent CO2 reduction performance in our system.

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Robustness of the excitation energy at scission as a novel probe of nuclear dissipation at high energy

Physical Review C ◽

10.1103/physrevc.86.034605 ◽

2012 ◽

Vol 86 (3) ◽

Cited By ~ 12

Author(s):

W. Ye ◽

N. Wang

Keyword(s):

Excitation Energy ◽

High Energy ◽

Nuclear Dissipation

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Transient changes in muscle high-energy phosphates during moderate exercise

Journal of Applied Physiology ◽

10.1152/jappl.1993.75.2.648 ◽

1993 ◽

Vol 75 (2) ◽

pp. 648-656 ◽

Cited By ~ 36

Author(s):

G. D. Marsh ◽

D. H. Paterson ◽

J. J. Potwarka ◽

R. T. Thompson

Keyword(s):

Oxygen Consumption ◽

Steady State ◽

Recovery Period ◽

High Energy ◽

Second Order ◽

Moderate Intensity ◽

High Energy Phosphates ◽

Order Model ◽

Time Constants ◽

First Order

The purpose of this study was to use 31P-nuclear magnetic resonance spectroscopy to examine changes in wrist flexor muscle metabolism during the transitions from rest to steady-state exercise (on-transient) and back to rest (off-transient). Five healthy young males (mean age 25 +/- 2 yr) performed a series of square-wave exercise tests, each consisting of 5 min of moderate-intensity work followed by a 5-min recovery period. The subjects repeated this protocol six times, and each individual's results were pooled before analysis. ATP and intracellular pH did not change significantly during exercise or recovery. Phosphocreatine (PCr) declined progressively at the onset of exercise, reaching a plateau after approximately 2 min. A reciprocal increase in Pi occurred during the onset of exercise. During the recovery period PCr was resynthesized, whereas Pi returned to resting levels. The data were plotted as a function of time and fit with both first- and second-order exponential growth or decay models; however, the second-order model did not significantly improve the fit of the data. Time constants for the first-order model of the on- and off-transient responses for both PCr and Pi were approximately 30 s. These values are nearly identical to the time constants for oxygen consumption during submaximal exercise that have been reported previously by several authors. The results of this study show that the metabolism of muscle PCr during steady-state exercise and recovery can be accurately described by a monoexponential model and, further, suggest that a first-order proportionality exists between metabolic substrate utilization and oxygen consumption.

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Studies about the Mechanism of Herbicidal Interaction with Photosystem II in Isolated Chloroplasts

Zeitschrift für Naturforschung C ◽

10.1515/znc-1979-1124 ◽

1979 ◽

Vol 34 (11) ◽

pp. 1010-1014 ◽

Cited By ~ 32

Author(s):

Gernot Renger

Keyword(s):

Electron Transport ◽

Photosystem Ii ◽

Excitation Energy ◽

Electron Acceptor ◽

Functional Organization ◽

Regulatory Element ◽

Release Kinetics ◽

Acceptor Side ◽

Receptor Sites ◽

Isolated Chloroplasts

Abstract Based on the functional organization scheme of system-II-electron transport and its modification by different procedures a proteinaceous component enwrapping the redox components (plastoquinone molecules) of the acceptor side (thereby acting as regulatory element) is inferred to be the unique target for herbicidal interaction with system II. This proteinaceous component, which is attacked by trypsin, provides the receptor sites for the herbicides. Studies of the release kinetics in trypsinated chloroplasts of the inhibition of oxygen evolution with K3 [Fe (CN)6] as electron acceptor indicates, that there exists a binding area with different specific subreceptor sites rather than a unique binding site for the various types of inhibitors. Furthermore, trypsination of the proteinaceous component enhances the efficiency of the plastoquinone pool to act as a non-photochemical quencher for excitation energy.

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Zooxanthellae Harvested by Ciliates Associated with Brown Band Syndrome of Corals Remain Photosynthetically Competent

Applied and Environmental Microbiology ◽

10.1128/aem.02292-06 ◽

2007 ◽

Vol 73 (6) ◽

pp. 1968-1975 ◽

Cited By ~ 27

Author(s):

Karin E. Ulstrup ◽

Michael Kühl ◽

David G. Bourne

Keyword(s):

Steady State ◽

Light Curve ◽

Light Exposure ◽

Fluorescence Analysis ◽

Coral Tissue ◽

Quantum Yields ◽

Symbiotic Association ◽

Gross Photosynthesis ◽

Brown Band ◽

Oxygen Measurements

ABSTRACT Brown band syndrome is a new coral affliction characterized by a local accumulation of yet-unidentified ciliates migrating as a band along the branches of coral colonies. In the current study, morphologically intact zooxanthellae (= Symbiodinium) were observed in great numbers inside the ciliates (>50 dinoflagellates per ciliate). Microscale oxygen measurements and variable chlorophyll a fluorescence analysis along with microscopic observations demonstrated that zooxanthellae within the ciliates are photosynthetically competent and do not become compromised during the progression of the brown band zone. Zooxanthellae showed similar trends in light acclimation in a comparison of rapid light curve and steady-state light curve measures of variable chlorophyll a fluorescence. Extended light exposure of steady-state light curves resulted in higher quantum yields of photosystem II. The brown band tissue exhibited higher photosynthetically active radiation absorptivity, indicating more efficient light absorption due to a higher density of zooxanthellae in the ciliate-dominated zone. This caused relatively higher gross photosynthesis rates in the zone with zooxanthella-containing ciliates compared to healthy coral tissue. The observation of photosynthetically active intracellular zooxanthellae in the ciliates suggests that the latter can benefit from photosynthates produced by ingested zooxanthellae and from photosynthetic oxygen production that alleviates diffusion limitation of oxic respiration in the densely populated brown band tissue. It remains to be shown whether the zooxanthellae form a stable symbiotic association with the ciliate or are engulfed incidentally during grazing on coral tissue and then maintained as active inside the ciliate for a period before being digested and replaced by new zooxanthellae.

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