ADPglucose synthesis

Thus, regulation of ADPGlc PPase, at both the transcriptional level and by allosteric control of the enzyme, modulates the rate of ADPglucose synthesis and starch synthesis. 

III. THE ADPglucose PATHWAY IS THE MAJOR PATHWAY OF STARCH SYNTHESIS in Vivo... 

An alternate pathway for starch synthesis has been proposed, which is based on the finding of a putative ADPGlc translocator in the envelope of both amyloplasts and chloroplasts. Akazawa et al. (1991) proposed that ADPglucose is synthesized in the cytosol by the sucrose synthase (rather than in the plastid by the action of the ADPGlc PPase, as is widely accepted), and is then transported into the plastid where it is converted into starch by the starch synthase. A critique of this hypothesis is presented in the chapter, The Site of Starch Synthesis in Nonphotosynthetic Plant Tissues The Amyloplast, where metabolite transport into the plastids is discussed, but it is worth mentioning here that this pathway does not fulfill the criteria mentioned in the preceding—that is, the experimental evidence does not support this alternative pathway. 

Spilatro, S. R., and Preiss, J. 1987. Regulation of starch synthesis in the bundle sheath and mesophyll of Zea mays L. Intercellular compartmentalization of enzymes of starch metabolism and the properties of the ADPglucose Pyrophosphorylases. Plant Physiol. 83, 621-627. 

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