The chlorophyll aII reaction in trypsin-treated spinach chloroplasts in the presence of potassium ferricyanide.

In trypsin-treated spinach chloroplasts there is no linear electron flow from water to potassium ferricyanide. The chlorophyll aII reaction, however, is still active but insensitive to 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea. From this we conclude that ferricyanide and trypsin together stimulate a mini-cycle in photosystem II.