Co-ordinated synthesis of gentiobiitol and sorbitol, evidence of sorbitol glycosylation in transgenic sugarcane

Sugarcane (a Saccharum spp. interspecific hybrid) was previously engineered to synthesize sorbitol (designated as sorbitolcane). Motivated by the atypical development of the leaves in some sorbitolcane, the polar metabolite profiles in the leaves of those plants were compared against a group of control sugarcane plants. Eighty-six polar metabolites were detected in leaf extracts by GC-MS. Principal component analysis of the metabolites indicated that three compounds were strongly associated with sorbitolcane. Two were identified as sorbitol and gentiobiose and the third was unknown. Gentiobiose and the unknown compound were positively correlated with sorbitol accumulation. The unknown compound was only abundant in sorbitolcane. This compound was structurally characterized and found to be a sorbitol-glucose conjugate. ¹³C NMR analysis indicated that the glucopyranose and glucitol moieties were 1,6-linked. Ligand exchange chromatography confirmed that the compound was a β-anomer, thus identifying the compound as 6-O-β-d-glucopyranosyl-d-glucitol, or gentiobiitol.