Compositional and enzymatic changes associated with the sugar-end defect in Russet Burbank potatoes

This study was initiated to determine the starch-sugar composition and the activities of relevant enzymes of carbohydrate metabolism in Russet Burbank (cv,) potatoes exhibiting the sugar-end defect. The frequency of sugar-end tubers was increased by applying a single, transient, moisture-deficit stress period following tuberization, The following properties were unique to sugar-end tubers compared to normal tuber tissue, (1) Starch and total solids decreased markedly while glucose content increased 15-fold, (2) The concentration of Suc was markedly lower, (3) Pi was slightly but significantly increased, (4) The activities of UGPase and Susy decreased nearly 3- and 2-fold, respectively, (5) The activity of AGPase decreased 50%, (6) The ratio of STPLase to AGPase shifted over 3-fold in favor of starch mobilization, (7) Basal AcInv activity (assayed in the presence of inhibitor) increased 7-fold during storage, (8) Tuber Glc concentration showed a better correlation to basal AcInv activity than to total AcInv activity (inhibitor destroyed), (9) Kinetic analysis suggested that the level and/or effectiveness of the AcInv inhibitor was decreased in the sugar-end tuber tissue. These results are discussed in relation to metabolic changes which occur in converting a starch storing tuber to one primarily involved with starch mobilization.