Photoinhibition: Impairment of the primary charge separation between P‐680 and pheophytin in photosystem II of chloroplasts

The question of the primary site of photoinhibition was investigated using the light‐induced absorbance change of pheophytin a (at 685 nm) in spinach chloroplasts and Chlamydomonas reinhardtii cells. Photoinhibition of spinach thylakoid membranes resulted in a parallel decrease in the amplitude of the pheophytin a (Δ A 685 ) and Q A (Δ A 320 ) photoreduction signals. In intact Chlamydomonas reinhardtii cells the pheophytin photoreduction and oxygen evolution activity exhibited a similar decrease during photoinhibition. A complete recovery of both activities was attained within 60 min incubation in normal growth conditions. It is concluded that the primary site of photoinhibition involves the components (P‐680 and/or pheophytin) of the primary charge separation.