STRUCTURAL DIVERSITY OF FRUCTAN IN RELATION TO THE TAXONOMY OF THE POACEAE

To test the hypothesis that fructan structure can be used as a taxonom ic character for the Poaceae we examined the accumulation of the linea r, beta-2,6-linked fructan series with a terminal glucose residue with in the tribes Aveneae and Poeae. Only Dactylis glomerata L. (Poeae) ha s been shown to contain this series, making it unique among fructan st ructures and a potential taxonomic marker. To this end, 13 members of the tribes Aveneae and Poeae were surveyed for the presence of this fr uctan series by comparing extracts of water-soluble carbohydrate by TL C with an extract of D. glomerata. The fructans of four species were s imilar to those of D. glomerata, as determined by TLC. Further compari son by anion-exchange chromatography and linkage analysis demonstrated that Phalaris aquatica L., Puccinellia stricta (Hook. f.) C. H. Blom and Holcus lanatus L. contained a linear, beta-2,6-linked series of fr uctan with a terminal glucose residue but that Lagurus ovatus L., alth ough containing predominantly beta-2,6-linked fructan was composed of more than one series of fructan, one with a terminal glucose residue a nd one with an internal glucose residue. A linear beta-2,6-Iinked seri es of fructans with a terminal glucose residue was the dominant fructa n accumulated by some species of genera belonging to both the Aveneae (Phalaris and Holcus) and the Poeae (Dactylis and Puccinellia). As bot h of these tribes also contain genera that accumulate fructans with an internal glucose residue, e.g. Avena and Lagurus (Aveneae) and Lolium (Poeae), structure of fructan cannot be used to distinguish these tri bes. Review of the literature, however, showed that it is possible to separate the supertribes Triticodae and Poodae on the basis of the str ucture of the fructan that they accumulate.