ONE OF THE FINAL FRONTIERS IN IMPROVING CROP PERFORMANCE IS THE EFFICIENT CONVERSION OF LIGHT ENERGY INTO BIOMASS IN PHOTOSYNTHETIC REACTIONS. THE PHOTOSYNTHETIC CAPACITY OF PLANTS IS CURRENTLY LIMITED BY CONSTANT PHOTODAMAGE INCURRED BY THEPHOTOSYSTEM II (PSII) PIGMENT-PROTEIN COMPLEX THROUGHOUT THE DAY. LIGHT AND HEAT-INDUCED REACTIVE OXYGEN SPECIES(ROS) IRREVERSIBLY DAMAGE THE PSII REACTION CENTER, NECESSITATING A CONCERTED DAMAGE AND REPAIR MECHANISM, WHILE CONCOMITANTLY PREVENTING THE DE NOVO SYNTHESIS OF A FUNCTIONAL D1 PROTEIN REQUIRED FOR ITS REASSEMBLY. IN ORDER TO MAXIMIZE THE VIABLE ENZYMATIC LIFESPAN OF PSII, PHOTOSYNTHETIC REENGINEERING STRATEGIES MUST RADICALLY IMPROVE UPON THE ENERGETICALLY COSTLY, ALBEIT NECESSARY, TASK OF RECYCLING THE DAMAGED REACTION CENTER.WHILE THIS LONG-TERM GOAL IS UNDOUBTEDLY ACHIEVABLE, IT REQUIRES A DETAILED UNDERSTANDING OF THE BASIC MOLECULAR MECHANISM BY WHICH DAMAGE MODULATES THE DISASSEMBLY AND REPAIR OF PSII. THEREFORE, THE RESEARCH PROPOSED HERE WILL INVESTIGATE THE MOLECULAR MECHANISMS BY WHICH ROS, A UBIQUITOUS COMPONENT OF OXYGENIC PHOTOSYNTHESIS,INDUCES THE DISASSEMBLY OF PSII. THE PROPOSED RESEARCH WILL IDENTIFY OXIDATIVE CHANGES TO THE COMPOSITIONOF PSII IN THE MODEL PLANT ORGANISM ARABIDOPSIS THALIANA, AND FURTHER DESCRIBE THE EFFECTS OF OXIDATIVE DAMAGE ON PSII DISASSEMBLY AND REPAIR USING SEVERAL BIOCHEMICAL STRATEGIES.