Identification of a mannitol transporter, AgMaT1, in celery phloem

A celery petiole phloem cDNA library was constructed and used to identify a cDNA that gives Saccharomyces cerevisiae cells the ability to grow on mann itol and transport radiolabeled mannitol in a manner consistent with a prot on symport mechanism. This cDNA was named AgMaT1 (Apium graveolens mannitol transporter 1). The expression profile in source leaves and phloem was in agreement with a role for mannitol in phloem loading in celery. The identif ication in eukaryotes of a mannitol transporter is important because mannit ol is not only a primary photosynthetic product in species such as celery b ut is also considered a compatible solute and antioxidant implicated in res istance to biotic and abiotic stress.