Xanthophyll-cycle based model of the rapid photoprotection of Nannochloropsis in response to regular and irregular light/dark sequences

Abstract

<p>We explore the photoprotection dynamics of Nannochloropsis oceanica using time-correlated single photon counting under regular and irregular actinic light sequences. The varying light sequences mimic natural conditions, allowing us to probe the real-time response of non-photochemical quenching (NPQ) pathways. Durations of fluctuating light exposure during a fixed total experimental time and prior light exposure of the algae are both found to have a profound effect on NPQ. These observations are rationalized with a quantitative model based on the xanthophyll cycle and the protonation of LHCX1. The model is able to accurately describe the dynamics of non-photochemical quenching across a variety of light sequences. The combined model and observations suggest that the accumulation of a quenching complex, likely zeaxanthin bound to a protonated LHCX1, is responsible for the gradual rise in NPQ. Additionally, the model makes specific predictions for the light sequence dependence of xanthophyll concentrations that are in reasonable agreement with independent chromatography measurements taken during a specific light/dark sequence.

Concluding remarks: Directing and controlling materials and molecules

“…3 shows the response of N. oceanica to varying periods of high light and dark along with a kinetic model of the feedback scheme sketched above. 13 Being a "bottom up" model, the model makes predictions for the carotenoid concentrations during such illumination sequences which are in reasonable accord with separate experimental measures of the predicted concentrations.…”

Modulation of xanthophyll cycle impacts biomass productivity in the marine microalgaNannochloropsis

“…The impact of zeaxanthin on NPQ can be assessed also by performing multiple NPQ-induction measurements, separated by a dark relaxation (22, 23) (Figure 2). In this protocol, most of NPQ relaxes after the first illumination step, following the dissipation of ΔpH across the thylakoid membrane.…”

Coupled charge and energy transfer dynamics in light harvesting complexes from a hybrid hierarchical equations of motion approach

“…This may have interesting implications for the understanding of non-photochemical quenching processes in light harvesting complexes. It is generally assumed that non-photochemical quenching is activated by conformational changes, induced by pH changes or chemical modifications of the protein or bound carotenoids, in protein-pigment complexes moving quenchers into positions where they can efficiently coupled to chromophores, 6,7,74,[79][80][81][82] thereby increasing the rate of charge transfer quenching and/or excitation energy transfer quenching. The work here highlights the potential role of the excita-tion energy funnel in CT quenching, and we suggest that nonphotochemical quenching could also be activated by changes in the site energies and couplings within the chromophore excited state manifold that funnel excitations towards quenching sites.…”

“…27,87 By combining existing computational tools with the hybrid HEOM/QME method, currently implemented in the freely available Matlab code HEOM-lab, 77 it may be possible to shed light on the precise mechanisms that produce nonphotochemical quenching in photosynthetic organisms, 6 for example how chemical modifications of carotenoids in the xanthophyll cycle activates NPQ in LHCII and related proteins like LHCX1. 7,79 For this reason we anticipate the method will become a useful tool in studying non-photochemical quenching and reaction center processes in photosynthetic systems.…”