Tansley Review No. 5 Fructans and the Metabolism of Sucrose in Vascular Plants

Abstract

SUMMARY The occurrence, structure and metabolism of fructose polymers in tissues of vascular plants are discussed in relation to the metabolism of sucrose. Distinctions are made between long‐term and short‐term storage of such polymers and the regulatory mechanisms which govern accumulation are examined. The roles of various fructosyltransferases in the synthesis of the different fructan structures from sucrose are outlined. The potential selective advantages of the possession of fructan metabolism in different species are assessed with reference to possible roles as cryoprotectants, in osmotic control and as storage carbohydrates whose metabolism can continue at low temperatures (0 to 5°C). It is concluded that the complexity and variety of fructan structures and of the associated enzyme systems has resulted in an incomplete understanding of their physiology and biochemistry, but their significance as an alternative storage polysaccharide in both leaves and storage organs should not be underestimated.

Transgenic potato tubers accumulate high levels of 1‐kestose and nystose: functional identification of a sucrose sucrose 1‐fructosyltransferase of artichoke (Cynara scolymus) blossom discs

“…Inulin molecules are polymers in which adjacent fructose residues are joined by 13-2,1 linkages whereas levan-type fructans are characterized by 13-2,6 bonds linking the fructosyl units (Pollock, 1986;Pollock and Cairns, 1991;Pollock and Chatterton, 1988). However, besides linear fructans many plants also store branched molecules of different linkage types (Housley and Pollock, 1993;Pollock, 1986;Pollock and Cairns, 1991;Pollock and Chatterton 1988).…”

Fructan variation in the rhizophores of Vernonia herbacea (Vell.) Rusby, as influenced by temperature

“…Since fructo-oligosaccharide accumulation is frequently correlated with plants exposed to low temperatures, it has been suggested that fructans may act as cryoprotectants (Eagles 1967, Wiemken et al 1986, Pollock & Chatterton 1988. Corroborating this hypothesis is the fact that grasses including cereals (wheat, oats and barley) accumulate fructans during winter (Meier & Reid 1982, Pontis & Del Campillo 1985, Pollock 1986, Chatertton et al 1989, Prud'home et al 1993. Also, several species of Asteraceae, as exemplified by chicory (Cichorium intybus L.), accumulate fructans of low degree of polymerization (DP) when exposed to chilling temperatures ( Van den Ende et al 1996).…”

“…Variation in fructan contents and composition have been associated not only with the plant growth but also with seasonal changes in temperature and other environmental factors (Pollock 1986, Pontis 1989, Housley & Pollock 1993, and references there in). Since fructo-oligosaccharide accumulation is frequently correlated with plants exposed to low temperatures, it has been suggested that fructans may act as cryoprotectants (Eagles 1967, Wiemken et al 1986, Pollock & Chatterton 1988.…”

Fructan content of wheat seedlings(Triticum aestivumL.) under hypoxia and following re‐aeration

“…For plants which suffer from oxygen deprivation (hypoxia), the carbohydrate supply can be of particular importance to cope with this environmental stress. Temperate grasses like wheat {Tri-ticum aestivum L.) are known to accumulate fructans mainly of low DP in vegetative tissues (Bancal & Gaudillere, 1989), whereas starch is deposited in the seeds and to lesser extent in leaf ehloroplasts (Pollock, 1986). The purpose of this article is to show how oxygen deficiency affects carbohydrate balance, especially in relation to fructans.…”