Effect of Salt Concentration on the Reverse Electron Flow and Membrane Potential Responsible for Stimulated Light Emission in Chloroplasts

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The effect of salt concentration on delayed and stimulated light emission in preilluminated broken chloroplasts was studied. It was possible to estimate both the contribution of the reverse electron flow from the plastoquinone pool to primary acceptor of PS II (Q) and the membrane potential responsible for stimulated light emission by measuring the intensities of delayed and stimulated luminescence in the presence and absence of DCMU. In the light emission stimulated by the acid-base transition, the reverse electron flow increased to more than three-fold that of the delayed light emission, and decreased as the salt concentration increased. The reverse electron flow, however, did not increase with stimulation by a KCl pulse; it remained nearly constant regardless of the salt concentration. The membrane potential and proton motive force, estimated from the stimulated light emissions due to the KCl pulse and the pH shift respectively, decreased as the salt concentration in the suspending medium increased. Since Cl^- can permeate the thylakoid membrane, the decrease in membrane potential was caused by increasing the concentrations of Cl^- which decreased the diffusion potential. The possibility of an increase in permeability of the membranes to Cl^- is discussed.
日本植物生理学会の論文