Galactinol synthase involved in the biosynthesis of raffinose family oligosaccharides (RFOs) that function as osmoprotectants. May promote plant stress tolerance. myo-inositol + UDP-alpha-D-galactose = alpha-D-galactosyl-(1->3)-1D-myo-inositol + H(+) + UDP Expressed in seeds, mostly in radicle tips. Accumulates in developing seeds during dry weight deposition and desiccation tolerance acquisition. Disappears after germination. Declines within 8 hours of imbibition in a gibberellin-dependent manner. Induced by dehydration but not by cold in germinating seeds, and induced by both dehydration and cold in leaves. Belongs to the glycosyltransferase 8 family. Galactosyltransferase subfamily.