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 Optimum pH is 6.0-7.0 for degradative reaction (PubMed:22184213, PubMed:17257168). Optimum pH is 7.0 for synthetic reaction (PubMed:22184213). Optimum pH is 9.0-9.5 for synthetic reaction (PubMed:17257168). A number of isoforms are produced. According to EST sequences. Detected in the whole plant but more precisely confined to the vasculature in cotyledons, leaves, petals, anthers and roots. No visible phenotype. Belongs to the glycosyltransferase 1 family. Plant sucrose synthase subfamily.