A comparison of the light-induced, non-reversible fluorescence quenching in Photosystem II with quenching due to open reaction centres in terms of the chlorophyll emission spectral forms

Abstract

The recent demonstration that the room temperature fluorescence emission spectrum of Photosystem II may be described as a linear combination of Gaussian bands associated with the well-known chlorophyll spectral forms (Zucchelli, G., Jennings, R.C., Garlaschi, F.M. (1992) Biochim. Biophys. Acta, 1099, 163–169) has permitted analysis of a number of fluorescence quenching phenomena in terms of the chlorophyll spectral forms. In this context we have analysed the fluorescence quenching due to open reaction centres and also the light-induced, non-photochemical, non-reversible quenching in isolated thylakoids, a Photosystem II membrane preparation and the major light-harvesting chlorophyll a/ b protein complex (LHCII). Whereas open reaction centres quench the emission associated with the spectral form chl 688 684 with greatest efficiency, thus indicating that it is this spectral form which is the most efficient in transferring energy to reaction centres, all the non-photochemical phenomena investigated show maximal quenching for both chl 680 678 and chl 687 684. It is concluded that the light-induced, non-photochemical, non-reversible quenching involves the generation of quenching centres within the Photosystem II antenna, possibly at the level of LHCII.