The synthesis of the D1 subunit of the reaction center of photosystem II is light-dependent in isolated chloroplasts. The mechanism of the regulation by light was analyzed using spinach chloroplasts. The light-regulated synthesis of the D1 protein was prevented by the addition of atrazine and the dependence on the concentration of atrazine of the inhibition was practically identical with that of the inhibition of photosynthetic electron transport in photosystem II, as measured by the photoreduction of 2,6-dichlorophenol indophenol. Inhibitors of photosynthetic phosphorylation, such as phloridzin, nigericin and carbonyl cyanidem-chlorophenylhydrazone, also inhibited the light-dependent synthesis of the D1 protein. Determination of the levels of ATP in chloroplasts and the rates of synthesis of D1 protein under the various degrees of inhibition caused by these reagents suggested that the level of ATP in the soluble, stromal fraction can control the synthesis of the D1 protein. The level of stromal ATP in chloroplasts was further manipulated, either by modulating the intensity of actinic light or by the addition of metabolites, such as glycerate, which was used to decrease the level of ATP in the light, and dihydroxyacetone phosphate/oxaloacetate, which was used to raise the level of ATP in the dark. The results definitely support the hypothesis that the light-induced level of ATP is an essential determinant in the regulation of the synthesis of the D1 protein in isolated chloroplasts.
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