Raffinose and Stachyose Accumulate in Hypocotyls during Drying of Common Buckwheat Seedlings

During seed maturation, common buckwheat (Fagopyrum esculentum Moench) embryos accumulate sucrose and alpha-galactosides of D-chiro-inositol (named fagopyritols), which are rare in plant tissues. Although fagopyritols are degraded rapidly during germination, buckwheat seedlings survive desiccation with resumption of growth of hypocotyl tissues but not radicle tissues on rehydration. The objectives were to determine if changes in soluble carbohydrates in hypocotyl and radicle tissues of buckwheat correlated with differential tissue survival after drying seedlings to 0.06 g of water g(-1) fresh weight. Buckwheat seeds completed germination between 12 and 24 h after the start of imbibition (HAI) coincident with the loss of survival of radicle tissues after drying. By contrast, hypocotyl tissues of the seedlings at 24, 36, and 48 HAI survived drying and on rehydration formed adventitious roots. During buckwheat seed maturation, embryo axis tissues accumulated sucrose and fagopyritols (64 and 81 mg g(-1) dry weight) but little raffinose and stachyose (0.2 and 1.7 mg g(-1)). During seed hydration, fagopyritols in axis tissues were hydrolyzed before the completion of germination. Sucrose, myo-inositol, and D-chiro-inositol are present in both hypocotyls and radicles before and after drying. During drying of 48-HAI buckwheat seedlings, hypocotyl tissues accumulated much more raffinose (23.2 mg g(-1)) and stachyose (8.3 mg g(-1)) than fagopyritols (2.8 mg g(-1)) whereas none of these compounds accumulated in radicle tissues that were sensitive to drying. An apparent shift in biosynthetic pathways within hypocotyls resulted in raffinose and stachyose accumulation but not fagopyritols during drying of common buckwheat seedlings. The survival of hypocotyl tissues correlated with an increase in concentrations of raffinose, stachyose, and sucrose.