Abstract
During soybean [Glycine max (L.) Merrill] seed development, seed coat tissues contain sucrose, myo-inositol, D-chiro-inositol, D-pinitol and low concentrations of galactinol. Low concentrations of fagopyritol B1, galactopinitols, and raffinose also accumulate in seed coats during mid-maturation and stachyose accumulates late in maturation. Traces of raffinose can be detected in cotyledons of young seeds (24 days after pollination) and infrequently in seed coat cup exudates at mid-seed fill. On gas chromatograms, questionable peaks corresponding to the retention time of raffinose may be observed in seed coat cup exudates. To determine if raffinose and stachyose can be unloaded from seed coats into the free space surrounding developing seeds, soybean stem-leaf-pod explants from plants with low-raffinose, low-stachyose seeds (LRS) or normal raffinose and stachyose seeds (CHECK) were fed solutions containing 10 mM raffinose or 10 mM stachyose via the cut stem for 3 days. Raffinose was present in leaf, pod and seed coat tissues after feeding raffinose or stachyose to explants. Small amounts of raffinose were unloaded into seed coat cups. Stachyose accumulated in leaf and pod tissues after feeding stachyose to explants, but stachyose was detected in only one of the 32 seed coat exudates assayed. Soybean seed coats unloaded raffinose in very small amounts that may explain the presence of trace amounts of raffinose in embryo tissues of young seeds.
Highlights
Soybean [Glycine max (L.) Merrill] leaf tissues contain the free cyclitols D-pinitol (1D-3-O-methyl-chiro-inositol), myo-inositol, D-chiro-inositol and D-ononitol (1D-4-Omethyl-myo-inositol), the non-reducing sugar sucrose, and the reducing sugars maltose, fructose, and glucose [1,2,3]
The raffinose family oligosaccharides, galactinol, galactopinitol A, fagopyritol B1, or their higher galactosyl oligomers generally are not detected in leaf blade tissues but are present in mature seeds
Composition of soluble carbohydrates in leaf extracts differed little among four soybean lines [3] with low raffinose and stachyose (LRS) seeds expressing the mutant stc1 phenotype [6,7,8], low raffinose, stachyose and phytin (LRSP1, LRSP2) seeds
Summary
Soybean [Glycine max (L.) Merrill] leaf tissues contain the free cyclitols D-pinitol (1D-3-O-methyl-chiro-inositol), myo-inositol, D-chiro-inositol and D-ononitol (1D-4-Omethyl-myo-inositol), the non-reducing sugar sucrose, and the reducing sugars maltose, fructose, and glucose [1,2,3]. Soybean stem-leaf-pod explants fed solutions containing free cyclitols have been used to demonstrate the accumulation of cyclitols and galactosyl cyclitols in seed coat and embryo tissues [15], whereas the unloading of sucrose, myo-inositol, D-pinitol, and D-chiroinositol in seed coat cup exudates has been demonstrated [16].
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