Glycosyl hydrolase family protein acting primarily as a highly specific galactosyltransferase (PubMed:25100720). Synthesizes digalactosyldiacylglycerol from monogalactosyldiacylglycerol in the absence of UDP-galactose in vitro (PubMed:14600212). Hydrolyzes o- and p-nitrophenyl beta-D-glucoside in vitro (PubMed:15258268). Plays a role in freezing tolerance (PubMed:15258268, PubMed:18466306, PubMed:20798281). May play a role in chloroplast protection (PubMed:18466306). 2 a 1,2-diacyl-3-O-(beta-D-galactosyl)-sn-glycerol = a 1,2-diacyl-3-O-[beta-D-galactosyl-(1->6)-beta-D-galactosyl]-sn-glycerol + a 1,2-diacyl-sn-glycerol Induced by MgCl(2). Optimum pH is 7.5. Optimum temperature is 24 degrees Celsius. Expressed in hypocotyls, cotyledons, stems, leaves, pedicels, sepals, anthers and pistils. Limited expression in roots. Not detected in petals or filaments. Not induced by cold, dehydration, salt or abscisic acid. Sensitive to freezing (PubMed:15258268, PubMed:20798281). Loss of tri- and tetragalactosyldiacylglycerol accumulation during freezing (PubMed:20798281). Belongs to the glycosyl hydrolase 1 family.