INACTIVATION AND PROTECTION OF PHOTOSYSTEM-2 PARTICLES DURING FREEZING

Prolonged storage of isolated photosystem 2 (PS2)-enriched subchloropl ast particles in the frozen state leads to a decrease of the PS2 activ ity and to an increase of the energy transfer between chlorophyll (Chl )-proteins of the light-harvesting chlorophyll a/b (LHC)-PS2 complex. The energy transfer was less influenced than the PS2-mediated electron transport at freeze-thaw treatment of PS2 particles. The change of th ese parameters was not affected by the rate of freezing. The addition of cryoprotectants such as glycerol, trehalose or saccharose in the su spension medium prior to freezing preserved to a different extent the PS2-mediated electron transport and the energy transfer between the Ch l molecules of the LHC-PS2 complex.