Sucrose-cleaving enzyme that provides UDP-glucose and fructose for various metabolic pathways. Functions in callose synthesis at the site of phloem sieve elements. an NDP-alpha-D-glucose + D-fructose = a ribonucleoside 5'-diphosphate + H(+) + sucrose Detected in the whole plant but more precisely confined to the vasculature in cotyledons, leaves, petals, anthers and roots. Also detected in developing siliques, young immature rosette and cauline leaves. No visible phenotype. Belongs to the glycosyltransferase 1 family. Plant sucrose synthase subfamily.