Mechanisms of light harvesting by photosystem II in plants

TL;DR

This study models how photosystem II in plants efficiently harvests light, revealing the role of membrane structure and excitation diffusion in energy transfer and quenching mechanisms.

Contribution

It introduces a structure-based model that simulates excitation energy flow in PSII with high accuracy, elucidating mechanisms previously experimentally inaccessible.

Findings

Excitation movement is diffusive, becoming subdiffusive at reaction centers.

Membrane morphology influences light harvesting efficiency via excitation diffusion length.

The model explains how nonphotochemical quenching affects PSII energy transfer.

Abstract

Light harvesting by photosystem II (PSII) in plants is highly efficient and acclimates to rapid changes in the intensity of sunlight. However, the mechanisms of PSII light harvesting have remained experimentally inaccessible. Using a structure-based model of excitation energy flow in 200 nanometer (nm) x 200 nm patches of the grana membrane, where PSII is located, we accurately simulated chlorophyll fluorescence decay data with no free parameters. Excitation movement through the light harvesting antenna is diffusive, but becomes subdiffusive in the presence of charge separation at reaction centers. The influence of membrane morphology on light harvesting efficiency is determined by the excitation diffusion length of 50 nm in the antenna. Our model provides the basis for understanding how nonphotochemical quenching mechanisms affect PSII light harvesting in grana membranes.