STRUCTURE OF FRUCTAN OLIGOMERS IN CHEATGRASS (BROMUS-TECTORUM L)

Leaves of field-grown cheatgrass (Bromus tectorum L.) plants were samp led during early spring when day- and night-time temperatures were rel atively cool. Fructan oligomers with a degree of polymerization (DP) 3 -6 were extracted and purified using gel and anion-exchange chromatogr aphy. The structures of 13 cheatgrass fructans were established. They included two trisaccharides [1-kestotriose (1-kestose) and 6-kestotrio se (6-kestose)], four tetrasaccharides [(1,1)-kestotetraose (nystose), (1&6)-kestotetraose (bifurcose), (6,1)-kestotetraose and (6,6)-kestot etraose], three pentasaccharides [(1,1&6)-kestopentaose, (1&6,6)-kesto pentaose 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 wh ich two fructose moieties are linked to the fructose subunit of each s ucrose molecule. Thus the dominant series is built upon (1&6)-kestotet raose. Fructans larger than DP 3 with exclusively 2-->1- or 2-->6-link ages were absent except for a very small amount of (6,6)-kestotetraose . The unique fructan structures synthesized in cheatgrass, wheat and o ats illustrate diversity in the enzymology of fructan biosynthesis amo ng grass species.