Structure of fructans in roots and leaf tissues of Lolium perenne

Summary An analysis of fructan structures, to increase the understanding of biosynthetic pathways and enzymology of fructan synthesis in root and leaf tissues of Lolium perenne is reported. Fructan extracted from stubble of L. perenne plants was analyzed by high performance anion exchange chromatography and pulsed amperometric detection (HPAEC‐PAD) using a new desalting technique. Structures of fructan isomers, separated up to DP16 (DP, degree of polymerization), were established by chromatographic elution times or by GC‐MS. Fructans of DP8 belonged essentially to three series: inulin series, inulin neoseries and the levan neoseries, which is/are different in glucose (terminal or internal) and linked fructose residues. High DP fructans (DP > 8) comprised 75% molecules with an internal glucose residue. They had some branch points although 1 and 6 kestotetraose could not be detected and the β(2–6) linked fructose residues were 70 times more abundant than the β(2–1) linked fructose residues. Roots, sheaths, leaf blades and elongating leaves accumulated similar fructans although amounts of both low and high, and types of low, DP fructans, differed. It is proposed that fructans in L. perenne are synthesized via four enzymes: 1‐SST (1‐sucrose‐sucrosefructosyl transferase), 1‐FFT (1‐fructan‐fructanfructosyl transferase), 6G‐FT (6‐glucose‐fructosyl transferase) and 6‐FFT (6‐fructan‐fructanfructosyl transferase) or 6‐SFT (6‐sucrose‐fructanfructosyl transferase).