# Energy-dependent quenching adjusts the excitation diffusion length to regulate photosynthetic light harvesting

## TL;DR

This study quantitatively links energy-dependent quenching (qE) to PSII light harvesting regulation by modeling excitation transfer in the grana membrane, revealing how quenching modulates excitation diffusion length and improves PSII yield predictions.

## Contribution

It introduces a pigment-scale model incorporating qE into excitation transfer, connecting molecular quenching to PSII yield at the membrane scale.

## Key findings

- Single molecule measurements support weak-quenching regime.
- Excitation transport modeled as 2D random walk with diffusion length.
- Diffusion-corrected lake model improves PSII yield estimates.

## Abstract

An important determinant of crop yields is the regulation of photosystem II (PSII) light harvesting by energy-dependent quenching (qE). However, the molecular details of excitation quenching have not been quantitatively connected to the PSII yield, which only emerges on the 100 nm scale of the grana membrane and determines flux to downstream metabolism. Here, we incorporate excitation dissipation by qE into a pigment-scale model of excitation transfer and trapping for a 200 nm x 200 nm patch of the grana membrane. We demonstrate that single molecule measurements of qE are consistent with a weak-quenching regime. Consequently, excitation transport can be rigorously coarse-grained to a 2D random walk with an excitation diffusion length determined by the extent of quenching. A diffusion-corrected lake model substantially improves the PSII yield determined from variable chlorophyll fluorescence measurements and offers an improved model of PSII for photosynthetic metabolism.