Structure of fructan oligomers in cheatgrass (Bromus tectorum L.) *

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Abstract
SUMMARY: Leaves of field‐grown cheatgrass (Bromus tectorum L.) plants were sampled during early spring when day‐ and night‐time temperatures were relatively cool. Fructan oligomers with a degree of polymerization (DP) 3–6 were extracted and purified using gel and anion‐exchange chromatography. The structures of 13 cheatgrass fructans were established. They included two trisaccharides [1‐kestotriose (1‐kestose) and 6‐kestotriose (6‐kestose)], four tetrasaccharides [(1.1)‐kestotetraose (nystose), (1&6)‐kestotetraose (bifurcose), (6,1)‐kestotetraose and (6,6)‐kestotetraose], three pentasaccharides [(1,1&6)‐kestopentaose, (1&6,6)‐kestopentaose and (6;1&6)‐kestopentaose] plus four hexasaccharides [(1,1,1&6)‐kestohexaose (1&6,6,6)‐kestohexaose, (6;1&6,6)‐kestohexaose and (6;1,6&6)‐kestohexaose]. All fructans larger then DP 4 contained a branch point. Each member of the dominant series(1&6)‐kestotetraose, (1&6,6)‐kestopentaose and (1&6,6,6)‐kestohexaose, is a branched fructan in which two fructose moieties are linked to the fructose subunit of each sucrose molecule. Thus the dominant series is built upon (1&6)‐kestotetraose. Fructans larger than DP 3 with exclusively 2→1‐ or 2→6‐linkages were absent except for a very small amount of (6,6)‐kestotetraose. The unique fructan structures synthesized in cheatgrass, wheat and oats illustrate diversity in the enzymology of fructan biosynthesis among grass species.