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Models and measurements of energy-dependent quenching.

Zaks J, Amarnath K, Sylak-Glassman EJ, Fleming GR - Photosyn. Res. (2013)

Bottom Line: In addition, we address the outstanding questions and challenges in the field.One of the current challenges in gaining a full understanding of qE is the difficulty in simultaneously measuring both the photophysical mechanism of quenching and the physiological state of the thylakoid membrane.We suggest that new experimental and modeling efforts that can monitor the many processes that occur on multiple timescales and length scales will be important for elucidating the quantitative details of the mechanism of qE.

View Article: PubMed Central - PubMed

Affiliation: Physical Biosciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, 94720, USA.

ABSTRACT
Energy-dependent quenching (qE) in photosystem II (PSII) is a pH-dependent response that enables plants to regulate light harvesting in response to rapid fluctuations in light intensity. In this review, we aim to provide a physical picture for understanding the interplay between the triggering of qE by a pH gradient across the thylakoid membrane and subsequent changes in PSII. We discuss how these changes alter the energy transfer network of chlorophyll in the grana membrane and allow it to switch between an unquenched and quenched state. Within this conceptual framework, we describe the biochemical and spectroscopic measurements and models that have been used to understand the mechanism of qE in plants with a focus on measurements of samples that perform qE in response to light. In addition, we address the outstanding questions and challenges in the field. One of the current challenges in gaining a full understanding of qE is the difficulty in simultaneously measuring both the photophysical mechanism of quenching and the physiological state of the thylakoid membrane. We suggest that new experimental and modeling efforts that can monitor the many processes that occur on multiple timescales and length scales will be important for elucidating the quantitative details of the mechanism of qE.

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Related in: MedlinePlus

Schematic of “fluorescence lifetime snapshots” measurements. The technique tracks changes on both the T timescale (sec to hours) as well as in the t timescale (ps to ns). qE triggering and the thylakoid membrane rearrangement occur on the T timescale. Quenching of chlorophyll fluorescence occurs on the t timescale and contains information about the membrane configuration
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Fig10: Schematic of “fluorescence lifetime snapshots” measurements. The technique tracks changes on both the T timescale (sec to hours) as well as in the t timescale (ps to ns). qE triggering and the thylakoid membrane rearrangement occur on the T timescale. Quenching of chlorophyll fluorescence occurs on the t timescale and contains information about the membrane configuration

Mentions: To fill this gap in techniques for measuring qE, we have developed a technique for measuring the changing fluorescence lifetime as qE turns on in plants and algae, which we call “fluorescence lifetime snapshots” (Fig. 10) (Amarnath et al. 2012). It is a two-dimensional (2D) technique with one time axis being the fluorescence decay time and the second being the adaptation/relaxation timescale. The technique has so far been used to measure the changes in fluorescence lifetimes in live cells of Chlamydomonas reinhardtii during the transition from a dark- to a light-acclimated state, and back to a dark-acclimated state. The data from the measurement on algae were globally fit to three exponential decays. This result suggested that the three lifetimes could be treated as separate pools of PSII that cannot transfer between each other. Two of the populations had lifetimes of 65 and 305 ps, with the third having a lifetime of 1 ns. The amplitudes of the two shorter lifetimes increased during the light treatment and decreased in the ensuing darkness. In addition, these amplitudes substantially decreased when the pH gradient was dissipated using nigericin. The amplitudes associated with the 65 and 305 ps lifetime components exhibited different dynamics during qE induction and relaxation, which led us to suggest that there are two different mechanisms associated with qE in C. reinhardtii. This technique correlates the T axis, which describes the timescales of qE triggering, with the t axis, which probes changes in the membrane and photophysical mechanism of qE.Fig. 10


Models and measurements of energy-dependent quenching.

Zaks J, Amarnath K, Sylak-Glassman EJ, Fleming GR - Photosyn. Res. (2013)

Schematic of “fluorescence lifetime snapshots” measurements. The technique tracks changes on both the T timescale (sec to hours) as well as in the t timescale (ps to ns). qE triggering and the thylakoid membrane rearrangement occur on the T timescale. Quenching of chlorophyll fluorescence occurs on the t timescale and contains information about the membrane configuration
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3824227&req=5

Fig10: Schematic of “fluorescence lifetime snapshots” measurements. The technique tracks changes on both the T timescale (sec to hours) as well as in the t timescale (ps to ns). qE triggering and the thylakoid membrane rearrangement occur on the T timescale. Quenching of chlorophyll fluorescence occurs on the t timescale and contains information about the membrane configuration
Mentions: To fill this gap in techniques for measuring qE, we have developed a technique for measuring the changing fluorescence lifetime as qE turns on in plants and algae, which we call “fluorescence lifetime snapshots” (Fig. 10) (Amarnath et al. 2012). It is a two-dimensional (2D) technique with one time axis being the fluorescence decay time and the second being the adaptation/relaxation timescale. The technique has so far been used to measure the changes in fluorescence lifetimes in live cells of Chlamydomonas reinhardtii during the transition from a dark- to a light-acclimated state, and back to a dark-acclimated state. The data from the measurement on algae were globally fit to three exponential decays. This result suggested that the three lifetimes could be treated as separate pools of PSII that cannot transfer between each other. Two of the populations had lifetimes of 65 and 305 ps, with the third having a lifetime of 1 ns. The amplitudes of the two shorter lifetimes increased during the light treatment and decreased in the ensuing darkness. In addition, these amplitudes substantially decreased when the pH gradient was dissipated using nigericin. The amplitudes associated with the 65 and 305 ps lifetime components exhibited different dynamics during qE induction and relaxation, which led us to suggest that there are two different mechanisms associated with qE in C. reinhardtii. This technique correlates the T axis, which describes the timescales of qE triggering, with the t axis, which probes changes in the membrane and photophysical mechanism of qE.Fig. 10

Bottom Line: In addition, we address the outstanding questions and challenges in the field.One of the current challenges in gaining a full understanding of qE is the difficulty in simultaneously measuring both the photophysical mechanism of quenching and the physiological state of the thylakoid membrane.We suggest that new experimental and modeling efforts that can monitor the many processes that occur on multiple timescales and length scales will be important for elucidating the quantitative details of the mechanism of qE.

View Article: PubMed Central - PubMed

Affiliation: Physical Biosciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, 94720, USA.

ABSTRACT
Energy-dependent quenching (qE) in photosystem II (PSII) is a pH-dependent response that enables plants to regulate light harvesting in response to rapid fluctuations in light intensity. In this review, we aim to provide a physical picture for understanding the interplay between the triggering of qE by a pH gradient across the thylakoid membrane and subsequent changes in PSII. We discuss how these changes alter the energy transfer network of chlorophyll in the grana membrane and allow it to switch between an unquenched and quenched state. Within this conceptual framework, we describe the biochemical and spectroscopic measurements and models that have been used to understand the mechanism of qE in plants with a focus on measurements of samples that perform qE in response to light. In addition, we address the outstanding questions and challenges in the field. One of the current challenges in gaining a full understanding of qE is the difficulty in simultaneously measuring both the photophysical mechanism of quenching and the physiological state of the thylakoid membrane. We suggest that new experimental and modeling efforts that can monitor the many processes that occur on multiple timescales and length scales will be important for elucidating the quantitative details of the mechanism of qE.

Show MeSH
Related in: MedlinePlus