Fructan 1-exohydrolases. beta-(2,1)-trimmers during graminan biosynthesis in stems of wheat? Purification, characterization, mass mapping, and cloning of two fructan 1-exohydrolase isoforms

Plant Physiol. 2003 Feb;131(2):621-31. doi: 10.1104/pp.015305.


Graminan-type fructans are temporarily stored in wheat (Triticum aestivum) stems. Two phases can be distinguished: a phase of fructan biosynthesis (green stems) followed by a breakdown phase (stems turning yellow). So far, no plant fructan exohydrolase enzymes have been cloned from a monocotyledonous species. Here, we report on the cloning, purification, and characterization of two fructan 1-exohydrolase cDNAs (1-FEH w1 and w2) from winter wheat stems. Similar to dicot plant 1-FEHs, they are derived from a special group within the cell wall-type invertases characterized by their low isoelectric points. The corresponding isoenzymes were purified to electrophoretic homogeneity, and their mass spectra were determined by quadrupole-time-of-flight mass spectrometry. Characterization of the purified enzymes revealed that inulin-type fructans [beta-(2,1)] are much better substrates than levan-type fructans [beta-(2,6)]. Although both enzymes are highly identical (98% identity), they showed different substrate specificity toward branched wheat stem fructans. Although 1-FEH activities were found to be considerably higher during the fructan breakdown phase, it was possible to purify substantial amounts of 1-FEH w2 from young, fructan biosynthesizing wheat stems, suggesting that this isoenzyme might play a role as a beta-(2,1)-trimmer throughout the period of active graminan biosynthesis. In this way, the species and developmental stage-specific complex fructan patterns found in monocots might be determined by the relative proportions and specificities of both fructan biosynthetic and breakdown enzymes.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Cell Wall / enzymology
  • Cloning, Molecular
  • DNA, Complementary / chemistry
  • DNA, Complementary / genetics
  • Glycoside Hydrolases / genetics
  • Glycoside Hydrolases / isolation & purification
  • Glycoside Hydrolases / metabolism*
  • Hydrogen-Ion Concentration
  • Isoenzymes / genetics
  • Isoenzymes / metabolism
  • Mass Spectrometry
  • Molecular Sequence Data
  • Phylogeny
  • Plant Stems / enzymology
  • Plant Stems / genetics
  • Plant Stems / growth & development
  • Sequence Analysis, DNA
  • Sequence Homology, Amino Acid
  • Substrate Specificity
  • Triticum / enzymology*
  • Triticum / genetics
  • Triticum / growth & development
  • beta-Fructofuranosidase


  • DNA, Complementary
  • Isoenzymes
  • Glycoside Hydrolases
  • beta-Fructofuranosidase
  • fructan beta-fructosidase

Associated data

  • GENBANK/AJ508387
  • GENBANK/AJ516025