RAFFINOSE SYNTHASE AND GALACTINOL SYNTHASE IN DEVELOPING SEEDS AND LEAVES OF LEGUMES

The raffinose family oligosaccharides (RFO) have been proposed to play roles in cold acclimation in plants, seed viability, and flatulence in humans after consumption of beans. Galactinol synthase (GS) and raffinose synthase (RS) are believed to be key enzymes in the biosynthesis of RFO. To begin to understand the roles proposed for RFO, we have begun a study of GS and RS in soybean and kidney beans. Both exchange and synthesis reactions of RS were detected in developing soy bean seed as early as 5 days after flowering (DAF). While the RS synthesis activity leveled off at 15 DAF, the RS exchange activity continued to increase up to 60 DAF. The RS exchange and synthesis activities also differed in their reaction kinetics, pH optima, and purification properties. GS activity was highest at the late stages of kidney bean development. Consistent with the proposed role of RFO in cold acclimation, the GS activities in the developing seeds and leaves of soybean and kidney bean increased 3-4-fold upon exposure of whole plants to 4 ®C. This is the first report of GS activity in kidney bean and RS in soybean. © 1990, American Chemical Society. All rights reserved.