Soluble carbohydrates in mature soybean seed after feeding d- chiro-inositol, myo-inositol, or d-pinitol to stem-leaf-pod explants of low-raffinose, low-stachyose lines

Abstract

Soybean [ Glycine max L. (Merrill)] embryos accumulate sucrose, raffinose and stachyose during seed development and maturation. Raffinose and stachyose in soybean feed products are not digested by monogastric animals, resulting in flatulence and fewer nutrients for growth. Three lines of soybean selected for low-raffinose and low-stachyose (LRS) or low-raffinose, low-stachyose and low-phytin (LRSP1, LRSP2) concentrations in mature seed were compared to a CHECK line with normal concentrations of raffinose, stachyose and phytin. To determine if increasing the supply of free cyclitols to developing seed of these lines results in increased accumulation of galactosyl cyclitols, soybean stem-leaf-pod explants of each line were fed solutions containing 10 mM d- chiro-inositol, 10 mM myo-inositol, or 10 mM d-pinitol, or a control solution without cyclitols for 7 days. Explants were air-dried for 14 days. Soluble carbohydrates were extracted from axis, cotyledon, and seed coat tissues of mature, dry seed and analyzed by high-resolution gas chromatography. Axis and cotyledons from mature seed of all modified lines had low concentrations of stachyose compared to the CHECK line when fed a control solution without cyclitols. Feeding d- chiro-inositol to explants increased fagopyritol B1 accumulation in mature seed from all lines. Feeding myo-inositol to explants increased stachyose accumulation in mature seed of LRSP1, but feeding d-pinitol to explants did not alter soluble carbohydrate composition of mature seed. These responses demonstrate that an increase in the supply of free d- chiro-inositol in maternal tissues can result in enhanced accumulation of fagopyritols in mature seed of low-raffinose and low-stachyose or low-raffinose, low-stachyose and low-phytin soybean.