Sucrose-cleaving enzyme that provides UDP-glucose and fructose for various metabolic pathways. an NDP-alpha-D-glucose + D-fructose = a ribonucleoside 5'-diphosphate + H(+) + sucrose Homotetramer or heterotetramer with SUS2. Expressed in root phloem and leaf mesophyll. Expressed in phloem tissues and aleurone layers of seeds and at lower levels in the pericarp and endosperm cells (at protein level). Predominantly expressed in elongating tissues including roots, developing leaves and internodes. Expressed early in seed development and then declines gradually and disappears (at protein level). In the caryopse, strongly expressed during the pre-storage phase, and the expression decreased thereafter. Up-regulated by sucrose, fructose and glucose. Up-regulated under elevated CO2 condition. Belongs to the glycosyltransferase 1 family. Plant sucrose synthase subfamily.