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Keywords:

  • Fructan;
  • starch;
  • sucrose;
  • cold tolerance;
  • osmoregulation

Summary

From an extensive literature survey and from analytical data of 130 species from the Sheffield flora, the physiological and molecular attributes, and occurrence of fructan are considered. The exceptionally high concentrations of fructan in many native species and its exclusive vacuolar location are noted. In view of the contention that fructan may function in low temperature tolerance, estimates are given of their maximum vacuolar concentration. For most species examined, this is unlikely to make a significant contribution to low temperature tolerance under the field conditions of the Sheffield flora. The association of high concentrations in the shoots of several species with high nuclear 2C DNA values is recorded. It is this correlation which may be of significance to several early-season growing species. By maintaining supplies of fructose and sucrose from vacuoles in tissue undergoing expansion at low temperatures (a feature associated with high DNA values), such species obviate the need for transport of carbohydrate over distance as in starch-storing species. By shortening supply lines at critical cold periods, fructan-rich species may have a considerable advantage over starch-storing, small-celled, transport-dependent species. However, such an advantage is not commonly exploited by the contemporary Sheffield flora. It is suggested that the ecological significance of fructan may best be seen in floras of the past or in contemporary floras undergoing more severe environmental stresses.