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In order to cope with the deleterious effects of excess light, photosynthetic organisms
have developed remarkable strategies where the excess energy is dissipated as heat
by the antenna system. In higher plants one main player in the process is the major
light harvesting antenna of Photosystem II (PSII), LHCII. In this paper we applied
Stark fluorescence spectroscopy to LHCII in different quenching states to investigate
the possible contribution of charge-transfer states to the quenching. We find that
in the quenched state the fluorescence displays a remarkable sensitivity to the applied
electric field. The resulting field-induced emission spectra reveal the presence of
two distinct energy dissipating sites both characterized by a strong but spectrally
very different response to the applied electric field. We propose the two states to
originate from chlorophyll-chlorophyll and chlorophyll-carotenoid charge transfer
interactions coupled to the chlorophyll exciton state in the terminal emitter locus
and discuss these findings in the light of the different models proposed to be responsible
for energy dissipation in photosynthesis.