Sucrose-cleaving enzyme that provides UDP-glucose and fructose for various metabolic pathways (By similarity). Functions in developing seeds by supplying substrates for the biosynthesis of storage products (PubMed:11910009). an NDP-alpha-D-glucose + D-fructose = a ribonucleoside 5'-diphosphate + H(+) + sucrose Activated by phosphorylation at Ser-10 by CPK23. Homotetramer or heterotetramer with SUS1. Predominantly expressed in the leaf tissues. Expressed in seeds, and at lower levels in roots. Expressed in leaf mesophyll and phloem (at protein level). Expressed early in seed development with a peak at 6 days after pollination (DAP) and then decreases slightly (at protein level). In the caryopse, slightly expressed during the pre-storage phase and was strongly expressed from the early to middle storage phase. By anaerobic stress. Up-regulated by sucrose, fructose and glucose and by sugar starvation. By submergence. Phosphorylated at Ser-10 by CPK23 in developing seeds. Belongs to the glycosyltransferase 1 family. Plant sucrose synthase subfamily.