Submitted to: Biochimica et Biophysica Acta
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/16/2006
Publication Date: 2/10/2007
Citation: Micha, D.K., Livingston, D.P., Premakumar, R., Zuther, E., Obel, N., Cacela, C., Heyer, A. 2007. Fructans from oat and rye: composition and effects on membrane stability during drying. Biochimica et Biophysica Acta. 1768:1611-1619. Interpretive Summary: Fructan is a carbohydrate-chain molecule similar to starch except it is composed of fructose molecules instead of glucose. It accumulates in plants during low temperatures which suggests that it may function as a storage carbohydrate. Correlations of fructan concentration with freezing and drought tolerance have also suggested that it may play a role in protecting membranes from abiotic stress. In this research we extracted fructan from oats (least winter hardy) and rye (most winter hardy cereal crop) and compared their ability to protect membranes during drought in a model membrane system. Surprisingly, the fructan from oat had a greater protection on membranes than that in rye. In addition fructan that had only 4 fructose molecules had the most protective effect. Large fructan (8 or more fructose's) had little if any protective effect. This research is the first time fructan from a specific crop species has been shown to directly affect the ability of membranes to withstand abiotic stress. It indicates that the overall survival of plants from freezing and drought is much more complicated than originally thought.
Technical Abstract: In addition to their role as storage carbohydrates, fructans have been implicated in the abiotic stress tolerance of plants, especially grasses and cereals. We have analyzed the fructan content of two cereal species (oat (Avena sativa) and rye (Secale cereale)) that differ in their abiotic stress tolerance, using high performance liquid chromatography (HPLC) and matrix-assisted laser desorption ionization – time of flight mass spectrometry (MALDI-TOF MS). Both species contain highly complex mixtures of fructans, with the degree of polymerization (DP) ranging from 3 to 17. These mixtures were fractionated by preparative size exclusion chromatography into five defined size classes (DP 3 to 7) and two size classes containing mainly high DP fructans (DP>7 short and long). All size classes were characterized by HPLC and MALDI-TOF MS, which revealed compositional differences between the fructans from oat and rye. To characterize possible functions in cellular stress tolerance, we used liposomes as a model system. The effects of the fructans on liposome stability during drying and rehydration were assessed as the ability of the sugars to prevent leakage of a soluble marker and liposome fusion. The two high DP fractions (DP>7) from both species were unable to protect liposomes, while the fractions containing smaller fructans were protective to different degrees. Protection showed an optimum at DP 4 and the DP 3, 4, and 5 fractions from oat were more protective than all other fractions from either species. In addition, we found evidence for synergistc effects in membrane stabilization in mixtures of low DP with DP>7 fructans. In some cases, such mixtures provided better protection than either of the fractions alone.