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 mannitol and transport radiolabeled mannitol in a manner consistent with a proton 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 identification in eukaryotes of a mannitol transporter is important because mannitol is not only a primary photosynthetic product in species such as celery but is also considered a compatible solute and antioxidant implicated in resistance to biotic and abiotic stress.