Localization of Fructan Metabolism in the Vacuoles Isolated from Protoplasts of Jerusalem Artichoke Tubers (Helianthus tuberosus L.).

Protoplasts were prepared from tubers of Helianthus tuberosus in the developing and in the resting stage of development. Vacuoles were isolated from the protoplasts and purified by sedimentation through a density gradient of glycine betaine. All the fructan (inulin) with a DP ⩾ 3 (i.e. the trisaccharide isokestose and larger polymers of fructose) was found to be located exclusively in the vacuoles whilst sucrose, glucose, and fructose were located only partially there. The vacuoles were also found to be the sole cell compartments containing fructan synthesizing enzyme activities (sucrose-sucrose-fructosyl-transferase and fructan-fructan-fructosyl-transferase) and fructan degrading enzyme activity (fructan exohydrolase), depending on the stage of development of the tubers. The vacuole is therefore proposed to be the cell organelle for fructan storage and metabolism.