Fructan biosynthesis in excised leaves of Lolium temulentum L.

SUMMARY Fructan oligosaccharides with degree of polymerization of 3–12 extracted from leaves of Lolium temulemtum L. were analyzed by normal‐phase thin‐layer chromatography. The pattern of oligosaccharides was more complex than that observed in tubers of Helianthus tuberosus L. and stem internodes of Hordeum vulgare L., indicating that fructans of multiple linkage types were present in this tissue. On the basis of co‐chromatography with known standards and constituent hexose analysis, two trisaccharides, neokestose (6‐G fructosyl sucrose) and isokestose (1‐F fructosyl sucrose) were found to accumulate to high concentrations. A third trisaccharide, thought to be kestose (6‐F fructosyl sucrose) was present at much lower tissue concentrations. An abundant tetrasaccharide with a chromatographic mobility similar to that of nystose (1‐F difructosyl sucrose) also accumulated. When carbohydrate‐depleted leaves were excised and continuously illuminated, total water‐soluble carbohydrate accumulation was linear with respect to time at a rate of 1–8 mg g ‐1 fresh mass over a 30 h period. In the first 6h sucrose accumulated to lOmgg1, at which time fructan biosynthesis was detected. Isokestose appeared first, followed by neokestose and subsequently kestose and longer oligo‐ and polyfructosides. Changes in the concentrations of these compounds, and their radioactivity following feeding of 14 CO 2 , was consistent with precursor‐product relationships between sucrose and trisaccharides, and between trisaccharides and oligo‐ and polyfructans.