The influence of the electric diffusion potential on delayed fluorescence light curves of chloroplasts treated with 3-(3,4-dichlorophenyl)-1,1-dimethylurea.

The potassium salt-induced transient increase of delayed fluorescence yield was studied in pea chloroplasts treated with 3-(3,4-dichlorophenyl)-1,1-dimethylurea. A simple kinetic model is proposed to account for the actinic light intensity dependence of the delayed fluorescence enhancement by the transmembrane diffusion potential induced by sudden salt addition. The electric field dependence of the rate constants for the recombination of primary separated charges with and without subsequent electronic excitation of reaction center chlorophyll was obtained. From the value of enhancement of delayed fluorescence by salt concentration gradients at saturating actinic light intensity, it is concluded that the distance, normal to thylakoid membrane surface, between the primary acceptor and the donor of Photosystem II is smaller than the membrane thickness.