FAGOPYRITOL B1, ALPHA-D-GALACTOPYRANOSYL-(1-]-2)-D-CHIRO-INOSITOL, A GALACTOSYL CYCLITOL IN MATURING BUCKWHEAT SEEDS ASSOCIATED WITH DESICCATION TOLERANCE

O-alpha-D-Galactopyranosyl-(1 --> 2)-D-chiro-inositol, herein named fa gopyritol B1, was identified as a major soluble carbohydrate (40% of t otal) In buckwheat (Fagopyrum esculentum Moench, Polygonaceae) embryos . Analysis of hydrolysis products of purified compounds and of the cru de extract led to the conclusion that buckwheat embryos have five alph a-galactosyl D-chiro-inositols: fagopyritol A1 and fagopyritol B1 (mon ogalactosyl D-chiro-inositol isomers), fagopyritol A2 and fagopyritol B2 (di-galactosyl D-chiro-inositol isomers), and fagopyritol B3 (tri-g alactosyl D-chiro-inositol). Other soluble carbohydrates analyzed by h igh-resolution gas chromatography included sucrose (42% of total), D-c hiro-inositol, myo-inositol, galactinol, raffinose and stachyose (1% o f total), but no reducing sugars. All fagopyritols were readily hydrol yzed by alpha-galactosidase (EC 3.2.1.22) from green coffee bean, demo nstrating alpha-galactosyl linkage. Retention time of fagopyritol B1 w as identical to the retention time of O-alpha-D-galactopyranosyl-(1 -- > 2)-D-chiro-inositol from soybean (Glycine max (L.) Merrill, Legumino sae), suggesting that the alpha-galactosyl linkage is to the 2-positio n of D-chiro-inositol. Accumulation of fagopyritol B1 was associated w ith acquisition of desiccation tolerance during seed development and m aturation in planta, and loss of fagopyritol B1 correlated with loss o f desiccation tolerance during germination. Embryos of seeds grown at 18 degrees C, a condition that favors enhanced seed vigor and storabil ity, had a sucrose-to-fagopyritol B1 ratio of 0.8 compared to a ratio of 2.46 for seeds grown at 25 degrees C. We propose that fagopyritol B 1 facilitates desiccation tolerance and storability of buckwheat seeds .