Direct Effects of Low Temperature upon Components of Fructan Metabolism in Leaves of Lolium temulentum L.

Abstract

Summary Specific effects of temperature upon fructan metabolism were measured in intact leaves of Lolium temulentum L. held at 5°C by comparing them with leaves where fructan accumulation at 20 °C had been induced by excision. Changes in fructose 2,6-bisphosphate contents differed markedly, with leaves at 5 °C showing a sustained decrease and excised leaves a marked increase, even though both treatments caused increased rates of sucrose accumulation in the tissue. Activity of cytoplasmic fructose-1,6-bisphosphatase, which is inhibited by fructose-2,6-bisphosphate, remained constant for 8 h following excision but increased by 64 % in chilled leaves. Measurements of incorporation of 14 CO 2 into oligosaccharides showed that chilled and excised leavesdiffered in the patterns of accumulation of radioactivity in trisaccharide isomers and the relative abundance of labelled tetra- and pentasaccharides, but not in the progressive movement of radioactivity from sucrose to high molecular weight fructan. Low incubation temperatures also affected the relative proportions of the different isomeric trisaccharides produced in vitro by crude SST and purified invertase preparations supplied with sucrose, mainly by increased accumulation of kestose. These results are discussed in relation to the effects of different environmental conditions during the induction of fructan synthesis in leaves of temperate gramineae.