The enclosed and exposed part of the peduncle of wheat (Triticum aestivum) – spatial separation of fructan storage

• Although fructan accumulation is reported in photosynthetically active organs, the long-term storage of fructan mainly occurs in more heterotrophic tissues. Significant amounts of fructan are stored in the internodes during grain filling of wheat (Triticum aestivum). The uppermost internode (peduncle) of wheat consists of a lower unexposed (i.e. enclosed by the flag leaf sheath and thus heterotrophic part, Pl) and an upper exposed autotrophic part (Pu). • Diurnal and long-term changes of fructan and sucrose (the precursor of fructan synthesis) contents were studied in Pl and Pu of potted wheat plants. • At mid grain-filling the sucrose concentration in Pu increased almost threefold during the light period and decreased in the following night. Diurnal changes in sucrose concentration were much less expressed in Pl. Fructan concentration was significantly higher in Pl than in Pu and did not change during the light period. • In another experiment, field grown wheat plants were sampled at regular intervals between 5 d before anthesis and grain maturity. At the time of maximum fructan content, 88% of the fructans in the total peduncle were stored in the heterotrophic Pl. Within Pl, fructan accumulation started in the older segments. The reason for the sharp separation of fructan storage between Pl and Pu remains unclear.