Photoinhibition Causes Loss of Photochemical Activity Without Degradation of D1 Protein

Illumination of isolated thylakoids or intact leaves with excess light resulted in a decline in photosynthetic activity measured as primary charge separation in photosystem II (ΔA320), photosystem II- dependent electron transport, or leaf oxygen evolution. It is concluded that the primary damage causing photoinhibition involves inactivation of the reaction centre function, and that degradation of Dl may be a consequence of that event.