Fructan synthesis in oat: I. Oligomer accumulation in stems during cold hardening and their in vitro synthesis in a crude enzyme extract.

The accumulation of fructan oligomers in cold hardened oat stems was compared to oligomer synthesis in a crude enzyme extract. Water-soluble carbohydrates were quantified at specified time intervals in three oat cultivars which had been hardened for a total of 5 wk at 2 °C. A crude enzyme extract was prepared from stems of one cultivar hardened for 6 d at 2 °C and incubated at 30 °C with 200 mM sucrose. 1-Kestose was the first oligomer to accumulate in vitro but neokestose rapidly increased after 3 h of incubation and eventually surpassed the level of 1 -kestose. Neokestose and 1-kestose accumulated at similar rates in vivo in the first week of hardening but after 1 week, 1-kestose began to decrease while neokestose remained relatively constant. The same phenomenon was observed in vitro but after only 3 h. 6-Kestose was not observed in vivo or in vitro, except for a trace before hardening began. The first tetramer to increase was 1&6 -kestotetraose but it subsequently decreased and its concentration was surpassed by that of 6 ,6-kestotetraose. Similarities and differences between in vivo and in vitro patterns of fructan synthesis are discussed.