The rise and fall of the photoinhibition-related energy dissipation q_I

Abstract

Photosynthesis converts sunlight into chemical energy, sustaining the vast majority of the biosphere. Photosystem II (PSII), the oxygen-forming enzyme that initiates photosynthesis, is however particularly prone to light-induced damage in a process known as photoinhibition, which limits the productivity of both aquatic and land photosynthesis. Photoinhibition is associated with an energy dissipation process of unknown origin, termed qI. Here, we present a detailed biophysical and biochemical in vivo study of qI in model green alga Chlamydomonas reinhardtii. Time-resolved fluorescence measurements demonstrate the origin of qI, and indicate the PSII reaction centre as the site of the quencher. Oxygen-dependence of quenching site formation, but not photoinhibition itself, is shown, suggesting that two types of PSII damage - donor and acceptor-side impairment - can be separated. We then demonstrate that the quenching loss takes place in the absence of PSII repair, and is mediated by the degradation of photoinhibited PSII cores by the FtsH protease. Finally, we integrate data ranging from picoseconds to hours in the context of structure-function excitation energy-transferring membrane patches, revealing the extent of PSII heterogeneity from the onset of photoinhibition until the breakdown of damaged PSII.

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“…This process involves the reversible redistribution of excitation energy between PSI and PSII mainly in low to moderate light conditions, although it might also be involved with protection against highlight in green algae (Allorent et al, 2013;Derks et al, 2015). The third component in the classical description of NPQ, qI, is associated with photoinhibition of PSII, with a relaxation time of tens of min to h. The qI quenching site was recently shown to likely reside in the D1 protein of a damaged PSII, and the relaxation of qI is linked to D1 degradation by FtsH protease in C. reinhardtii (Nawrocki et al, 2021). An additional component, named qZ, was identified based on the correlation between the slow (tens of min) formation and reconversion of Zx and the chlorophyll fluorescence relaxation.…”