Disentangling the sites of non-photochemical quenching in vascular plants

In nature, plants experience large fluctuations in light intensity and they need to balance the absorption and utilization of this energy accordingly. Non-photochemical quenching (NPQ) is a rapidly-switchable mechanism which protects plants from photodamage caused by high light exposure by dissipating the energy absorbed in excess as heat. It is triggered by the ΔpH across the thylakoid membrane and requires the presence of the protein PsbS and the xanthophyll zeaxanthin. However, the site and mechanism of the quencher(s) remain equivocal. Here, we constructed a mutant of Arabidopsis thaliana which lacks LHCII, the main antenna complexes of plants, to verify its contribution to NPQ. The mutant has normally stacked thylakoid membranes, displays no upregulation of other LHCs but shows a relative decrease in PSI which compensates for the decrease of the PSII antenna. The mutant exhibits a ~60% reduction in NPQ, while the remaining NPQ resembles that of the Chl b-less mutant, which lacks all PSII peripheral antenna complexes. We thus report that PsbS-dependent NPQ mainly occurs within LHCII, but there is an additional quenching site within the PSII core.