Polyol transporters in plants: celery as a model

Abstract

Polyols are reduced forms of aldose and ketose sugars. The most frequently found polyols in plants are mannitol, sorbitol and galactitol as well as an ubiquitous cyclitol, myo-inositol. Polyols such as mannitol and sorbitol are direct products of photosynthesis in parallel with sucrose. Polyols and sucrose serve similar functions such as long-distance translocation of carbon skeletons and energy between source and sink organs. Information on the transport of polyols is rather scarce and the last results from this field will be presented. A particular attention will be given to celery where the different steps of long-distance transport of both sucrose and mannitol have been investigated. A mannitol transporter (AgMaT1) that could be involved in phloem loading was recently cloned in our group and it was surprising to find homologies with transporters of unknown functions found in plants that do not synthesize mannitol (Arabidopsis and sugar beet). Some examples of the changes in the respective expression of the sucrose transporter and the mannitol transporter in several physiological situations will be given.