STRUCTURES OF FRUCTAN OLIGOMERS IN ORCHARDGRASS (DACTYLIS-GLOMERATA L)

Chemical structures of and relationships among the fructan oligomers (< DP9) in orchardgrass (Dactylis glomerata) were determined in this study. Although all three fructan trisaccharides, 1-kestotriose* (1-kestose), 6-kestotriose (6-kestose), and 6G-kestotriose (neokestose) occur in orchardgrass, 6-kestotriose is most prevalent. In contrast, cheatgrass (Bromus tectorum) and wheat (Triticum aestivum) do not contain 6G-kestotriose. 1-Kestotriose is the most common trisaccharide in cheatgrass while either 1-kestotriose or 6-kestotriose is dominant in wheat depending upon the environmental conditions and stage of plant development. Although 6-kestotriose is not present 1-kestotriose and 6G-kestotriose occur in similar amounts in oat (Avena sativa). 1&6-kestotetraose (bifurcose), a tetrasaccharide that includes both 1-kestotriose and 6-kestotriose moieties, is the most prevalent DP4 fructan in cheatgrass. In contrast, 6G, 6-kestotetraose and 6,6-kestotetraose are the major tetrasaccharides in oats and orchardgrass, respectively. The dominant oligosaccharides in orchardgrass, the DP3 through DP8 fructans-6-kestotriose, 6,6-kestotetraose, 6,6,6-kestopentaose, 6,6,6,6-kestohexaose, 6,6,6,6,6-kestoheptaose and 6,6,6,6,6,6-kestooctaose, each contain a terminal glucose and only 6-fructofuranosyl bonds. They appear to be part of the series that also constitutes the large oligosaccharides in wheat, Poa travialis and Lolium temulentum and are called graminins as proposed by Waterhouse and Chatterton (1993). The variety of fructan structures found in different species indicate that plants have evolved species - or possibly genera - specific fructan-synthesizing enzyme systems. Some plant species appear to form fructan oligomers that are characteristic of a particular plant group. Additional research is needed to determine the effects of plant parts, stage of development, and of interacting environmental factors on fructan biosynthetic enzyme activities and on the resultant fructan structures.