Submitted to: Recent Advances in Fructooligosaccharides Research
Publication Type: Review article
Publication Acceptance Date: 7/8/2006
Publication Date: 3/3/2007
Citation: Livingston, D.P., Hincha, D., Heyer, A. 2007. The relationship of Fructan to abiotic stress tolerance in Plants. Recent Advances in Fructooligosaccharides Research. p. 181-199. Interpretive Summary: Fructan is a plant carbohydrate that is composed of fructose molecules hooked together in a chain, similar to starch. It has been the subject of numerous studies for at least 200 years. Some of its' unique properties have made it a candidate for research investigating mechanisms of resistance to freezing, drought and salt stress. The purpose of this article is to bring the reader up to date with regard to some of the newer findings in fructan research and how these findings impact our knowledge of freezing and drought stress. Research in the 1800 and most of the 1900's considered fructan to be a ready supply of individual fructose molecules that the plant could release from the chain and use to lower the freezing point of water in the plant or use the sugars to help maintain pressure within cells as freezing and drought removed water. While these proposed mechanisms have never been proven false, recent research has indicated that fructan has the capacity to protect membranes by becoming embedded within the matrix of the membrane which strengthens it against rupture. In addition, plants that normally do not accumulate fructan were induced to do so by transferring genes from plants that do accumulate fructan. The drought and freezing tolerance of these transformed plants increased as a result of their new ability to accumulate fructan. These studies all support the importance of fructan in helping plants resist abiotic stress but leave room for gobs of research on exact mechanisms.
Technical Abstract: Fructan has long been recognized as a crucial component of drought and freeze protection in plants. Much of the early research considered how hexose sugars from fructan hydrolysis effected the chemical potential of water. Hence, numerous studies were published that attempted to correlate fructan concentrations with freezing and drought tolerance. As model membrane systems became available, investigations to study the effect of fructan on liposomes were initiated. These studies indicated that a direct interaction between membranes and fructan was possible. This new area of research began to move fructan and its' association with stress beyond mere correlation by confirming that fructan has the capacity to stabilize membranes during drying by inserting at least part of the polysaccharide into the lipid headgroup of the membrane. This helps prevent leakage when water is removed from the system either during freezing or drought. In addition to evidence from studies with model membranes, when plants were transformed with the ability to synthesize fructan, a concomitant increase in drought and or freezing tolerance was confirmed. While exact mechanisms are still open for consideration it has become clear that besides an indirect effect of supplying tissues with hexose sugars when the need arises, fructan has a direct protective effect that can be demonstrated by both model systems and genetic transformation. These studies will help breeders as they attempt to combine favorable genes into agronomically acceptable cultivars and extend their cultivation into regions where they currently cannot be grown.