Metabolism of glucose 6-phosphate by plastids from developing pea embryos

The aim of this work was to investigate the metabolism of glucose 6-phosphate by plastids isolated from developing pea (Pisum sativum L.) embryos. Plastids metabolise exogenously supplied glucose 6-phosphate via the pathway of starch synthesis and the oxidative pentose-phosphate pathway. The flux through the latter pathway is greatly stimulated by the provision of glutamine and 2-oxoglutarate — the substrates of glutamate synthase — indicating that it is regulated by the demand for reductant within the plastid. Flux in the presence of glutamine and 2-oxoglutarate is about 20% of the maximum flux through the pathway of starch synthesis. There is no competition for glucose 6-phosphate between the two pathways at concentrations which are saturating for both. Isolated plastids do not convert glucose 6-phosphate to amino acids or fatty acids at significant rates under the conditins of our experiments.Abbreviations ADPG adenosine 5-diphosphoglucose We thank Mike Emes (Department of Cell and Structural Biology, University of Manchester, UK) for valuable advice during the course of this work, and for making unpublished information available to us. We also thank Mark Stitt (Botanisches Institut der Universität, Heidelberg, FRG) and our colleagues, particularly Kay Denyer and Lionel Hill, for their helpful and constructive criticism. This work was supported by funding from the European Community, under contract C11* 0417-UK (SMA).