Differences in fructan accumulated in induced and field‐grown wheat plants: an elongation‐trimming pathway for their synthesis

Abstract

summaryMature blades of wheat seedlings were induced to form fructan by excision and continuous illumination, and their sugars were analyzed either 24 or 60 h after induction by both gel permeation and high performance liquid chromatography. The earliest accumulated fructan consisted mainly of 1‐kestose, nystose, bifurcose, and short oligomers rich in (2→1)‐linkages and branch point residues. After several days, fructan included more than fifty compounds, among which one‐half of the total were heptamers or larger. Oligomers accumulated during long‐term incubation contained a higher proportion of (2→6)‐linkages than those accumulated early after induction. Stems of field‐grown wheat contained about the same amount of fructan as blades of induced seedlings, but with larger proportions of phlein oligomers initiating with 6‐kestose, phlein‐like oligomers initiating with bifurcose, and other branched oligomers enriched in (2→6)‐linkages. An ‘elongation‐trimming’ pathway is proposed in which a (2→1)‐specific fructan fructosyl transferase and O‐6 branching activity produce branched oligomers rich in (2→1)‐linkages, and in which a fructan exo‐hydrolase cleaves 1‐linked terminal‐fructosyl units selectively to have phlein‐like oligomers resistant to further hydrolysis.