Sustained quenching not always means photoinhibition

Abstract

Photosynthetic light harvesting complexes (LHC) are involved in light absorption and energy dissipation. By modulating the photosystems absorption cross section, they affect their photosynthetic activity and non-photochemical quenching (NPQ) capacity. These processes have been widely studied by spectrally integrated chlorophyll fluorescence methods, which mask their associated spectral information. We explored in aspen and Arabidopsis npq mutants how the absence of these components affects the development of NPQ spectra under two contrasting conditions: in the absence and presence of photoinhibition. We proposed a new parameter to estimate the development of new emitting species (NESD) during time-spectrally resolved NPQ inductions and a pipeline to disentangle PSII energy partitioning heterogeneity. We demonstrate that LHCB, PsbS and zeaxanthin is required for NESD. By combining gas exchange with spectrally resolved kinetics, we show that under photoinhibitory conditions, however, NES develops in the absence of PsbS and zeaxanthin, and the resulting sustained quenching occurring independently of photoinhibition. Furthermore, we found that in the absence of LHCB and Curvature Thylakoid 1 a significant increase in photoinhibition was observed. This suggest that in the long term effective photoprotection requires the presence of LHCB and thylakoid plasticity, while PsbS and zeaxanthin play a major role in catalyzing LHCII-dependent quenching.