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Resolving the contribution of the uncoupled phycobilisomes to cyanobacterial pulse-amplitude modulated (PAM) fluorometry signals.

ABSTRACT: Pulse-amplitude modulated (PAM) fluorometry is extensively used to characterize photosynthetic organisms on the slow time-scale (1-1000 s). The saturation pulse method allows determination of the quantum yields of maximal (F(M)) and minimal fluorescence (F(0)), parameters related to the activity of the photosynthetic apparatus. Also, when the sample undergoes a certain light treatment during the measurement, the fluorescence quantum yields of the unquenched and the quenched states can be determined. In the case of cyanobacteria, however, the recorded fluorescence does not exclusively stem from the chlorophyll a in photosystem II (PSII). The phycobilins, the pigments of the cyanobacterial light-harvesting complexes, the phycobilisomes (PB), also contribute to the PAM signal, and therefore, F(0) and F(M) are no longer related to PSII only. We present a functional model that takes into account the presence of several fluorescent species whose concentrations can be resolved provided their fluorescence quantum yields are known. Data analysis of PAM measurements on in vivo cells of our model organism Synechocystis PCC6803 is discussed. Three different components are found necessary to fit the data: uncoupled PB (PB(free)), PB-PSII complexes, and free PSI. The free PSII contribution was negligible. The PB(free) contribution substantially increased in the mutants that lack the core terminal emitter subunits allophycocyanin D or allophycocyanin F. A positive correlation was found between the amount of PB(free) and the rate constants describing the binding of the activated orange carotenoid protein to PB, responsible for non-photochemical quenching.

SUBMITTER: Acuna AM

PROVIDER: S-EPMC4673099 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Optimized amplitude modulated multiband RF pulse design.

Project description:PurposeMultiband pulses are characterized by highly temporally modulated waveforms. Rapid phase or frequency modulation can be extremely demanding on the performance of radiofrequency (RF) pulse generation, which can lead to errors that can be avoided if pulses are restricted to amplitude modulation (AM) only. In this work, three existing multiband pulse design techniques are modified to produce AM waveforms.Theory and methodsMultiband refocusing pulses were designed using phase-optimization, time-shifting, and root-flipping. Each technique was constrained to produce AM pulses by exploiting conjugate symmetry in their respective frequency domain representations. Pulses were designed using the AM and unconstrained techniques for a range of multiband factors (ie, number of simultaneously excited slices), time-bandwidth products, and slice separations. Performance was compared by examining the resulting effective pulse durations. Phantom and in vivo experiments were conducted for validation.ResultsAcquired data confirmed that AM pulses can produce precise results when unconstrained designs may produce artifacts. The average duration of AM pulses is longer than the unconstrained versions. Averaged across a range of parameters, the duration cost for AM pulses was 26, 38, and 20% for phase-optimizing, time-shifting and root-flipping, respectively.ConclusionsAmplitude modulation multiband pulses can be produced for a relatively small increase in pulse duration. Magn Reson Med 78:2185-2193, 2017. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

| S-EPMC5697703 | biostudies-literature

Phycobilisomes linker family in cyanobacterial genomes: divergence and evolution.

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| S-EPMC8707847 | biostudies-literature

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| S-EPMC4585685 | biostudies-literature

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| S-EPMC9397104 | biostudies-literature

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| S-EPMC9606259 | biostudies-literature

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