Soluble oligosaccharides and galactosyl cyclitols in maturing soybean seeds in planta and in vitro

Stachyose, sucrose, and other non-reducing soluble carbohydrates are associated with the onset of desiccation tolerance during seed development and with seed storability. Mature soybean [Glycine mar (L) Merr.] seeds contain several galactosyl cyclitols in addition to sucrose, stachyose, and raffinose, but except for galactinol, the accumulation of these galactosyl cyclitols has not been reported for developing soybean seeds. Fifteen soluble carbohydrates including members of the raffinose, galactinol, galactopinitol, and fagopyritol series were analyzed in extracts from axis and cotyledon tissues of seeds and zygotic embryos matured in planta and in vitro. Galactopinitol A, galactopinitol B, and fagopyritol B1 accumulate in axis tissues of developing soybean seeds in planta in association with the onset of desiccation tolerance, yellowing of axis tissues, and in parallel with stachyose accumulation. Galactopinitol A, galactopinitol B, fagopyritol B1, and stachyose also accumulate in parallel in cotyledons in planta and in axis tissues during in vitro growth of zygotic embryos at 15 and 25 degrees C. Axes of soybean seeds matured at 25 degrees C contained higher concentrations of sucrose, raffinose, D-pinitol, D-chiro-inositol, fagopyritol El, and total soluble carbohydrates than axes of seeds matured at 18 degrees C. Soybean seeds accumulate mostly galactosyl pinitols and only small amounts of free pinitol. In future work, It would be of interest to determine if galactosyl cyclitols may substitute for the role of stachyose in providing desiccation tolerance and prolonged seed storability.