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 how much NPQ is occurring at each of these locations. Here, we perform time-resolved fluorescence measurements on WT and antenna mutants lacking LHCII (NoL) and all peripheral antenna (Ch1 and Ch1lhcb5). By combining the results with those of 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 60-70% of quenching occurs in LHCII, 15-20% in the minor antenna and 15-20% in the PSII core.