Models and measurements of energy-dependent quenching

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.

Knocking Down of Isoprene Emission Modifies the Lipid Matrix of Thylakoid Membranes and Influences the Chloroplast Ultrastructure in Poplar

“…The NPQ relaxation kinetics in the dark was used to calculate qE. qE was assigned as a fast-relaxing component (within the first 2 min of dark relaxation after switching off the actinic light), calculated as qE = (F m 99 -F m 9)/F99 m, 2min dark (Zaks et al, 2013).…”

Principles of light harvesting from single photosynthetic complexes

“…To prevent a build-up of excess energy, plants and algae dissipate this energy through a series of multi-time-scale processes. These processes are collectively known as non-photochemical quenching (NPQ) [37]. The short-time, energy-dependent component of NPQ is qE, and is triggered by a pH drop in the lumen and the resulting electrochemical gradient across the membrane [37,38].…”

“…While many of the time scales of NPQ have been identified, the mechanism and specific PPC responsible for quenching remains under debate. Specifically, which PPC, which carotenoid, and whether or not charge transfer states play a role have all been discussed [37][38][39].…”

Single-Molecule Identification of Quenched and Unquenched States of LHCII

“…In the reaction center, the excitation energy initiates an electron transfer chain to drive downstream biochemistry 2 . Notably, higher plants regulate the energy transport process so that the amount of excitation energy does not exceed the capacity of the reaction center [5][6][7][8] . This regulation, known as non-photochemical quenching (NPQ), protects the reaction center by preventing a build-up of absorbed energy, which would in turn generate deleterious photoproducts 9,10 .…”

“…One component of NPQ is the dissipation of excess energy during periods of intense sunlight. Although the antenna complexes are the site of dissipation, which antenna complex and what is the molecular mechanism of dissipation remain under debate 5,6,11 .…”