Regulation of Photosynthetic Electron Transport in Intact Spinach Chloroplasts

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Abstract
Relatively high concentrations of monovalent salts (150 millimolar) stimulated light-saturated uncoupled rates of O2 evolution linked to oxaloacetic acid (OAA) reduction by intact chloroplasts 2-to 3-fold. In contrast, monovalent salts partially inhibited light-saturated rates of O2 evolution coupled to CO2 fixation and uncoupled rates of nitrite reduction. In the presence of high salt concentration, light-saturated rates of electron transport were about equivalent for all three terminal electron acceptors. It is inferred that exogenous monovalent salts have at least two effects on photosynthetic electron transport, independent of photophosphorylation and CO2 metabolism: a partial inhibitory effect common to OAA, NO2− and CO2 reduction and a marked stimulatory effect unique to the photoreduction of OAA.