The effect of platelet activating factor on electron transport of spinach chloroplasts.

It was found that platelet activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) inhibits electron transport greater than 90% in Photosystem II of spinach chloroplasts in concentrations from 2.8 to 3.5 micrograms/ml. The inhibition of the main pathway of electron transport through Photosystem II appeared to be specific for the platelet activating factor. Phorbol myristate acetate, 1,2-dipalmitin or fatty acid esters gave 17-32% inhibition in higher concentrations. The inhibition site for platelet activating factor was localized close to the reaction center of Photosystem II, based on the inhibition of the donor reaction, diphenyl carbazide----indophenol, in Tris-treated chloroplasts. Other Photosystem II reactions, H2O----silicomolybdic acid, H2O----2,5-dimethylbenzoquinone, or H2O----indophenol, were also inhibited by platelet activating factor. The present data point out the unique inhibition of Photosystem II electron transport by the platelet activating factor, but do not support the operation of a phosphoinositide cycle in chloroplasts.