The effect Mg2+ on the reduction of NADP by an artificial electron donor

The effect of Mg2+ on the light-dependent reduction of NADP by an artificial electron donor has been investigated with isolated broken chloroplasts. In both short and long wavelength actinic light, addition of the salt under most conditions stimulates the yield and the saturation rate. The magnitude of the stimulation is a function of pH. The data indicate that previous interpretations of the Mg2+ effect in this system invoking changes in the spill-over rate between the photosystems is no longer tenable. It is suggested that addition of the salt causes activation of inactive reaction centers.