EMERSON ENHANCEMENT, PHOTOSYNTHETIC CONTROL AND PROTEIN-PHOSPHORYLATION IN ISOLATED MAIZE MESOPHYLL CHLOROPLASTS - DEPENDENCE UPON CARBON METABOLISM

Intact chloroplasts isolated from maize mesophyll have been used to investigate the relationship between the metabolic demand for ATP and the control of light-harvesting and electron transport. It was found that the rate of reduction of glycerate 3-phosphate can be either inhibited or stimulated by the addition of pyruvate, depending on their relative concentrations, pointing to optimisation of the ΔpH and the rate of electron transport. Pyruvate addition was associated with a stimulation of the phosphorylation of the light-harvesting chlorophyll protein complex, even when O2 evolution was stimulated. Under a variety of conditions, the level of phosphorylation was inversely correlated with the ΔpH. Emerson enhancement of the reduction of glycerate 3-phosphate is increased when pyruvate is added; the increased rate of O2 evolution brought about by far-red light is associated with an increase in the ΔpH. It is suggested that the ΔpH transmits the metabolic demand for ATP to the thylakoids, which respond by altering the relative rates of excitation of Photosystems I and II. © 1990.