Nucleotide sugars are either synthesized from phosphorylated monosaccharides or through epimerization of precursor nucleotide sugars4. UDP-Glc, first isolated and studied by Leloir, is a key metabolite of carbohydrate metabolism in both photosynthetic and nonphotosynthetic plant tissues. Nucleotide sugars represent between 10-25% of the total nucleotide pool of plants. Uridine nucleotides and in particular UDP-Glc predominate in the nucleotide-sugar pool of most plant tissues. UDP-Glc contributes between 60-70% of total nucleotide-sugars followed by UDP-D-Galactose (UDP-Gal) making up 15-25%. In young and mature leaves, the main photosynthetic tissues, UDP-Glc is used for sucrose synthesis by sucrose phosphate synthase and sucrose synthase to a lesser degree8. In addition, UDP-Glc is either used in cell wall synthesis
(cellulose, callose, mixed β(1-3)(1-4)-glucans) or enters the interconversion pathways and is
used indirectly as wall precursors. UDP-Glc also supplies the Glc units incorporated in
glycolipids and glycoproteins6.