The quantitative contribution of different Photosystem II compartments to non-photochemical quenching in Arabidopsis

Excess excitation energy in the light-harvesting antenna of Photosystem II (PSII) can cause irreversible damage to the photosynthetic apparatus. In periods of high light intensity, a feedback mechanism known as non-photochemical quenching (NPQ) induces the formation of quenchers, which can safely dissipate excess excitation energy as heat. Although quenchers have been identified in more than one compartment of the PSII supercomplex, there is currently no quantitative description of the extent to which NPQ occurs at each of these locations. Here, we perform time-resolved fluorescence measurements on Arabidopsis thaliana WT and antenna mutants lacking LHCII trimers (koLHCII) and all peripheral antenna (Ch1lhcb5). By combining the results with those from steady-state fluorescence experiments, we are able to estimate the intrinsic rate of NPQ for each plant and each PSII compartment. It is concluded that more than 70% of quenching occurs in LHCII, less than 10% in the minor antenna, and the rest is associated with the PSII core. Excess excitation energy is dissipated from Photosystem II as heat. Here the authors show that more than 70% of excess energy is quenched in the major light-harvesting antenna with smaller contributions from the minor antenna and photosystem core.