Free cyclitol unloading from seed coats on stem–leaf–pod explants of low-raffinose, low-stachyose, low-phytin soybean

Abstract

AbstractRaffinose, stachyose and phytin are undesirable compounds for soybean food and animal feed products. In seeds, raffinose and stachyose are believed to contribute to desiccation and cold stress tolerance. Thus, removal of these compounds from soybean by genetic mutation has resulted in a more commercially desirable composition, but potentially less physiologically viable seeds. In an effort to develop a method to improve viability and seed storability in soybean, stem–leaf–pod explants of three low raffinose, low stachyose lines, two of which were also low in phytin, and a check line were fed solutions containing d-chiro-inositol, myo-inositol or d-pinitol, free cyclitols which unload through the seed coat to the developing embryo where they accumulate as fagopyritols, galactinol and galactopinitols, respectively, during seed maturation. Increased galactopinitol and fagopyritol accumulation may substitute for the roles of raffinose and stachyose in low raffinose, stachyose and phytin seeds. Explants of all lines unloaded d-chiro-inositol, myo-inositol and d-pinitol. Fed d-chiro-inositol accumulated in leaf tissues demonstrating uptake into explants. Fed d-chiro-inositol and myo-inositol accumulated in pod wall and seed coat tissues of one or more lines. The results indicate that d-chiro-inositol was unloaded from the seed coat to the embryo in increased amounts after feeding. The potential use of increased maternal d-chiro-inositol for synthesis of fagopyritols in embryos to improve seed performance in low-stachyose and low-phytin soybean seeds is supported. The seed coat cup unloading of fed free cyclitols may provide a model system to test effective unloading of upregulated maternally synthesized cyclitols.