Light-induced fluorescence quenching in the light-harvesting chlorophyll a/b protein complex.

Irradiation of the principal photosystem II light-harvesting chlorophyll-protein antenna complex, LHC II, with high light intensities brings about a pronounced quenching of the chlorophyll fluorescence. Illumination of isolated thylakoids with high light intensities generates the formation of quenching centres within LHC II in vivo, as demonstrated by fluorescence excitation spectroscopy. In the isolated complex it is demonstrated that the light-induced fluorescence quenching: a) shows a partial, biphasic reversibility in the dark; b) is approximately proportional to the light intensity; c) is almost independent of temperature in the range 0-30°C; d) is substantially insensitive to protein modifying reagents and treatments; e) occurs in the absence of oxygen. A possible physiological importance of the phenomenon is discussed in terms of a mechanism capable of dissipating excess excitation energy within the photosystem II antenna.