May promote plant stress tolerance (By similarity). Galactinol synthase mainly involved in the biosynthesis of transport raffinose family oligosaccharides (RFOs) that function as osmoprotectants. myo-inositol + UDP-alpha-D-galactose = alpha-D-galactosyl-(1->3)-1D-myo-inositol + H(+) + UDP Present in phloem-associated intermediary cells. Weakly expressed in leaves. By cold. Follows a circadian rhythm; accumulates mostly at the dark phase transition. Belongs to the glycosyltransferase 8 family. Galactosyltransferase subfamily.