Mature dry legume seeds may contain up to 30 different soluble carbohydrates. Sucrose is a major component of the total soluble carbohydrates; others include the raffinose family oligosaccharides (RFOs; raffinose, stachyose, verbascose) that are mono-, di- and tri-α-galactosyl derivatives of sucrose. Other galactosides may include α-galactosyl derivatives of the cyclitols myo-inositol (galactinol, digalactosyl myo-inositol and trigalactosyl myo-inositol), d-pinitol (galactopinitol A, digalactosyl pinitol A (ciceritol) and trigalactosyl pinitol A; and galactopinitol B; higher galactosyl oligomers of galactopintiol B have rarely been detected), d-chiro-inositol (fagopyritol B1, fagopyritol B2 and fagopyritol B3) and d-ononitol (galactosyl d-ononitol and digalactosyl d-ononitol). Small amounts of myo-inositol, d-pinitol and d-chiro-inositol may also be present. Raffinose, stachyose and verbascose increase late in seed maturation, with 70% of RFOs accumulating after maximum seed dry weight is attained. RFOs are mostly degraded during germination. Sucrose, myo-inositol, d-pinitol and d-chiro-inositol are synthesized in maternal tissues of some legumes and are transported to and unloaded by seed coats into the apoplastic space surrounding developing seed embryos. Free cyclitols may be 60% of total soluble carbohydrates in leaves and 20% in seed coat cup exudates. Increasing the supply of free cyclitols may increase the accumulation of their respective α-galactosides in mature seeds. Seeds with reduced RFO accumulation, but with normal to elevated concentrations of galactosyl cyclitols (including fagopyritols), have normal field emergence and are also tolerant to imbibitional chilling under laboratory conditions. Molecular structures, biosynthetic pathways, accumulation of soluble carbohydrates in response to seed-expressed mutations and the physiological role of galactosides are reviewed.

Feeding stem–leaf–pod explants with d-chiro-inositol and d-pinitol was used as a method to modify α-d-galactosides in developing pea (Pisum sativum) seeds. Four genotypes differing in the composition of raffinose, stachyose and verbascose (raffinose family oligosaccharides or RFOs) in seeds – high RFOs (cv. Tiny), low RFOs (SZD175) and low verbascose (cv. Hubal and cv. Wt 506) – were studied. Although seeds of all examined pea lines were able to take up both d-chiro-inositol and d-pinitol, only d-chiro-inositol was effectively converted into its galactosides: mainly fagopyritol B1 (O-α-d-galactopyranosyl-(1 → 2)-d-chiro-inositol) and fagopyritol B2 (O-α-d-galactopyranosyl-(1 → 6)-O-α-d-galactopyranosyl-(1 → 2)-d-chiro-inositol). In seeds of pea lines naturally containing low levels of verbascose (cv. Hubal) and low RFOs (SZD175), the enhanced accumulation of fagopyritols depressed the RFO level by c. 64 and 20%, respectively. Moreover, in both genotypes, about 25 and 30% of total galactose bound in α-d-galactosides occurred in fagopyritols. d-Pinitol present in the pea seeds was converted into monogalactosides, but their accumulation was several-fold lower than that of fagopyritols and did not significantly influence the accumulation of RFOs. Pea seeds with the composition of soluble carbohydrates modified by feeding with either of the cyclitols were able to complete germination.

Maturing yellow lupin seeds were desiccation tolerant. Glucose, sucrose and cyclitols (mainly D-pinitol, D-chiro-inositol and myo-inositol) were predominant at the early stages of seed growth. Accumulation of the raffinose family oligosaccharides (RFOs) and the galactosyl cyclitols including galactinol, digalactosyl myo-inositol, galactopinitol A, galactopinitol B, trigalactopinitol A, ciceritol, fagopyritol B1 and fagopyritol B2 appeared during seed maturation; their increase correlated with seed germinability after desiccation. The loss of desiccation tolerance after seed germination was also studied. For the desiccation tolerance test, intact seedlings were dried rapidly or slowly followed by rehydration. Soluble carbohydrates were assayed before and after drying. Root tissues were more sensitive to desiccation than hypocotyl tissues and completely lost desiccation tolerance within 36 h of imbibition after both fast and slow-drying treatments. Survival of hypocotyls decreased gradually up to 96 h after imbibition. Loss of RFOs and galactosyl cyclitols in axis tissues preceded visible germination. Loss of desiccation tolerance was accompanied by loss of RFOs and galactosyl cyclitols and an increase in reducing sugars in cotyledon, hypocotyl and radicle tissues. Drying did not induce the accumulation of RFOs and galactosyl cyclitols in seedling tissues.