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United States Department of Agriculture

Agricultural Research Service

Title: Fructan Synthesis in Oat: I. Oligomer Accumulation in Stems During Cold Hardening and Their in Vitro Synthesis in a Crude Enzyme Extract

item Livingston D P,

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 11, 1993
Publication Date: N/A

Interpretive Summary: Fructan is a starch-like carbohydrate but is made of fructose instead of glucose molecules. In a previous study, the difference in the way the fructose molecules are attached in chains of 3, 4, and 5 sugars indicated that fructan in oat is different than that found in barley, wheat, and rye, but similar to that in ryegrass. In this study, enzymes which produce the unique fructan structures were isolated from oat stems. The enzymes were stimulated to produce fructan outside the plant by adding sucrose. The types and amounts of fructan produced by the isolated enzymes were compared to those produced in normal plant tissue. Most of the same fructan compounds were synthesized by the isolated enzymes, but they were produced at a much faster rate. This information will be used to help purify the enzymes involved in fructan production in oats. This will help identify reasons why oat stores so little fructan and is so susceptible to freezing temperatures.

Technical Abstract: The accumulation of fructan oligomers in cold hardened oat stems was compared to oligomer synthesis in a crude enzyme extract. Water extractable carbohydrates were quantified at specified time intervals in three oat cultivars which had been hardened for a total of 5 weeks at 2 degrees C. A crude enzyme extract was prepared from stems of one cultivar hardened for 6 days at 2 degrees C and incubated at 30 degrees C with 2 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 at a relatively constant level. The same phenomenon was observed in vitro, but after only 3 hours. 6-kestose was not observed in vivo or in vitro, except for a trace before hardening began. The first tetramer to increase was 1 and 6G-kestotetraose, but it subsequently decreased and its concentration was surpassed by that of 6G,6-kestotetraose. Similarities and differences between in vivo and in vitro patterns of fructan synthesis are discussed.

Last Modified: 3/2/2015
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