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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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Scenarios that give rise to indistinguishable fluorescence yield measurements, but that can be distinguished by fluorescence lifetime measurements. a Illustration of fluorescence lifetimes of quenching (case A1, solid line), which reduces the fluorescence lifetime, and bleaching (case A2, dashed line), which reduces the overall fluorescence amplitude. These two situations could give the same fluorescence yields even thought they display different fluorescence lifetimes. b Illustration of fluorescence lifetimes of moderate quenching of all fluorophores (case B1, solid line) and strong quenching of a small fraction of fluorophores (case B2, dashed line) which cannot be differentiated using fluorescence yield measurements
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Fig7: Scenarios that give rise to indistinguishable fluorescence yield measurements, but that can be distinguished by fluorescence lifetime measurements. a Illustration of fluorescence lifetimes of quenching (case A1, solid line), which reduces the fluorescence lifetime, and bleaching (case A2, dashed line), which reduces the overall fluorescence amplitude. These two situations could give the same fluorescence yields even thought they display different fluorescence lifetimes. b Illustration of fluorescence lifetimes of moderate quenching of all fluorophores (case B1, solid line) and strong quenching of a small fraction of fluorophores (case B2, dashed line) which cannot be differentiated using fluorescence yield measurements

Mentions: The chlorophyll fluorescence lifetime measures the relaxation of the chlorophyll excited state and contains information about the energy transfer network of the grana membrane. The benefits of lifetime measurements can be seen in scenarios that give rise to the same fluorescence yield, but different fluorescence lifetimes. Figure 7a illustrates the difference between quenching (A1), in which the lifetime of the excited state is shortened, and bleaching (A2), in which the number of fluorophores decreases. Because the fluorescence yield, which is measured in the PAM experiment, is equal to the area under the fluorescence lifetime curve, PAM measurements cannot differentiate between bleaching and quenching. Figure 7b illustrates how two different energy transfer networks can be resolved by measuring fluorescence lifetimes, but not by measuring fluorescence yields.Fig. 7


Models and measurements of energy-dependent quenching.

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

Scenarios that give rise to indistinguishable fluorescence yield measurements, but that can be distinguished by fluorescence lifetime measurements. a Illustration of fluorescence lifetimes of quenching (case A1, solid line), which reduces the fluorescence lifetime, and bleaching (case A2, dashed line), which reduces the overall fluorescence amplitude. These two situations could give the same fluorescence yields even thought they display different fluorescence lifetimes. b Illustration of fluorescence lifetimes of moderate quenching of all fluorophores (case B1, solid line) and strong quenching of a small fraction of fluorophores (case B2, dashed line) which cannot be differentiated using fluorescence yield measurements
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig7: Scenarios that give rise to indistinguishable fluorescence yield measurements, but that can be distinguished by fluorescence lifetime measurements. a Illustration of fluorescence lifetimes of quenching (case A1, solid line), which reduces the fluorescence lifetime, and bleaching (case A2, dashed line), which reduces the overall fluorescence amplitude. These two situations could give the same fluorescence yields even thought they display different fluorescence lifetimes. b Illustration of fluorescence lifetimes of moderate quenching of all fluorophores (case B1, solid line) and strong quenching of a small fraction of fluorophores (case B2, dashed line) which cannot be differentiated using fluorescence yield measurements
Mentions: The chlorophyll fluorescence lifetime measures the relaxation of the chlorophyll excited state and contains information about the energy transfer network of the grana membrane. The benefits of lifetime measurements can be seen in scenarios that give rise to the same fluorescence yield, but different fluorescence lifetimes. Figure 7a illustrates the difference between quenching (A1), in which the lifetime of the excited state is shortened, and bleaching (A2), in which the number of fluorophores decreases. Because the fluorescence yield, which is measured in the PAM experiment, is equal to the area under the fluorescence lifetime curve, PAM measurements cannot differentiate between bleaching and quenching. Figure 7b illustrates how two different energy transfer networks can be resolved by measuring fluorescence lifetimes, but not by measuring fluorescence yields.Fig. 7

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