Exciton annihilation as a probe of the light-harvesting antenna transition into the photoprotective mode

Non-photochemical quenching, NPQ, is the process by which plants protect themselves against photo-damage by converting excess excitation energy into harmless heat. Aggregation of the major light-harvesting complexes LHCII in vitro is associated with similar quenching and its molecular mechanism is considered to be the same as that of NPQ. Although aggregates present a useful model system, the analysis of their time-resolved data is complicated by the uncertainty and heterogeneity of their size. Recently NPQ has been induced in vitro also in isolated, non-aggregated LHCII complexes. We used this new quenching model to study the dynamics of excitation energy migration in quenched state unaffected by aggregation. The obtained dependency of the decay times of chlorophyll electronic excitations depending on sample conditions allowed us to conclude that LHCII is an extremely adaptable biological macromolecule capable of adjusting its structural and spectral properties to the varying environmental conditions. (C) 2012 Elsevier B.V. All rights reserved.