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. C ontents I. Introduction II. The structure of fructans in vascular plants: variations on a theme 2 III. The enzymes of fructan synthesis: common elements and sources of structural diversity 5 IV. The comparative biology of fructan metabolism: diversity in occurrence and function 11 V. Concluding remarks 19 Acknowledgements 19 References 19