Phosphate translocation in the regulation of photosynthesis

The plastid phosphate translocators located in the inner envelope membrane of chloroplasts and nongreen plastids mediate important translocation steps during the allocation of photoassimilates from sourceto sink-tissues. Repression of the chloroplast translocator severely alters diurnal carbon partitioning between leaves and sink tissues. Under physiological conditions, the translocator mediates a strict counterexchange of substrates. However, experiments with the reconstituted translocator demonstrate that transport can also occur by a channel-like uniport mechanism resulting in drastically increased transport rates. The chloroplast translocator is different from the analogous protein of non-green tissues. In all tissues examined, the translocator of non-green plastids only accepts glucose-6-phosphate in addition to phosphate and phosphorylated C3-compounds. The glucose-6-phosphate is subsequently used for starch synthesis.