galactinol

Galactinol (C12H22O11) is a glucose-derived cyclitol that serves as the activated donor of galactosyl units in the biosynthesis of raffinose family oligosaccharides (RFOs). It is synthesized from UDP‑galactose and myo‑inositol by the enzyme galactinol synthase (GOLS) in the cytosol of higher plants. The resulting compound consists of a galactose moiety linked α‑1,2 to myo‑inositol, forming a stable, water‑soluble carbohydrate.

Galactinol functions primarily as a galactosyltransferase substrate, providing the galactosyl group for the formation of raffinose, stachyose and related oligosaccharides through the action of raffinose synthase and stachyose synthase. These RFOs act as compatible solutes that help maintain cellular osmotic balance, stabilize membranes and proteins, and protect against abiotic stresses such as drought, salinity, and cold temperatures. Accumulation of galactinol and its derived oligosaccharides has been correlated with increased stress tolerance in multiple species, including Arabidopsis thaliana, rice, and soybean.

Beyond its role in stress physiology, galactinol participates in the transport of carbon and nitrogen within the phloem, and it may influence seed development and germination by modulating the availability of carbon reserves. The expression of GOLS genes is inducible by environmental cues, hormonal signals such as abscisic acid, and developmental stages, reflecting its integration into broader metabolic networks.

Galactinol is not typically found in significant amounts in animal tissues, and dietary exposure occurs mainly through consumption of plant-derived foods containing RFOs. Its metabolic pathway and stress‑protective properties continue to be subjects of research aimed at improving crop resilience and productivity.