Feeding stem-leaf-pod explants of pea (Pisum sativum L.) with D-chiro-inositol or D-pinitol modifies composition of α-D-galactosides in developing seeds

Feeding stem-leaf-pod explants with D-chiro-inositol and D-pinitol was used as a method to modify alpha-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-alpha-D-galactopyranosyl-(1 -> 2)- D-chiro-inositol) and fagopyritol B2 (O-alpha-D-galactopyranosyl-(1 -> 6)-O-alpha-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 a-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.