Figure 5.

Overview of the characterized metabolite transporters of the heterotrophic plastid. Non-photosynthetic plastids rely on the import of photosynthates to drive the metabolic reactions in the sink tissues. Glucose 6-phosphate is transported by GPT to provide heterotrophic plastids with substrates further used to produce reducing equivalents and storage compounds. In maize, the substrate for starch synthesis, ADP-glucose, is produced in the cytoplasm and shuttled to the seeds by the brittle-1 transporter. Abbreviations: ADP-Glc, ADP-glucose; BT1, Brittle-1 ADP-glucose carrier; Glc 1-P, glucose 1-phosphate; Glc 6-P, glucose 6-phosphate; GPT, glucose 6-phosphate/phosphate translocator; Mal, maltose; NTT, nucleoside triphosphate transporter; OPPP, oxidative pentose phosphate pathway; 3-PGA, 3-phosphoglyceric acid; PEP, phosphoenolpyruvate; Pi, inorganic phosphate; PPi, pyrophosphate; PPT, PEP/phosphate translocator; XPT, xylulose 5-phosphate/phosphate translocator; Xul 5-P, xylulose 5-phosphate.