Occurrence of fructans in the Gramineae (Poaceae)

The occurrence and type of storage carbohydrate (fructan, starch or sucrose) was determined in stems of reproductive tillers of a number of species of the family Gramineae representing major taxonomic groups. Plants were collected from two grassland sites in Victoria (Australia). Fructans were detected in all species examined, but particularly high concentrations were found in species of the subfamily Pooideae where fructans accounted for 75-95% of the storage carbohydrates. In most other subfamilies, fructans varied between 5 and 30% of the storage carbohydrates. However, fructans accounted for 50% of the storage carbohydrates in species of the subfamily Arundinoideae. Separation of fructans (to DP 14) by thin-layer chromatography demonstrated that different isomers of trisaccharides and different proportions of oligosaccharides were present, depending on the species. In some species there was evidence of continuous series of oligosaccharides between sucrose and high molecular weight polymers. However, these series differed markedly from the series of oligosaccharides present in Helianthus tuberosus. The polymerization of fructans and trisaccharide forms present in the grasses examined were similar on generic and, in a number of cases, subtribal and tribal levels and reflected phylogenetic relationships between taxa. The possible presence of fructans in all subfamilies may indicate that fructan synthesis is not necessarily exclusive to the subfamily Pooideae.