Action of salicylaldoxime on electron transport reactions, fluorescence yield, and light-induced field changes in spinach chloroplasts: A new mode of inhibition in photosystem II

Salicylaldoxime (1–10 mm) inhibits chloroplast electron transport reactions by a reversible and an irreversible modification of photosystem II. The irreversible inhibition correlates with removal of the loosely bound pool of manganese associated with the water-splitting mechanism. The reversible inhibition is characterized by (i) a suppression of artificial donor reactions, (ii) a high initial fluorescence yield, and (iii) a decline in the amplitude of the flash-induced electric field across the membrane. After removal of the inhibitor, the initial fluorescence yield declines to near-control levels, but the variable portion of the fluorescence rise remains missing. Addition of an artificial donor restores the variable fluorescence yield and normal electron transport rates to 2,6-dichlorophenolindophenol. Characteristics of the reversible inhibition suggest that salicylaldoxime causes suppression of photochemical charge separation in photosystem II.