CHANGES OF CARBOHYDRATES, METABOLITES AND ENZYME-ACTIVITIES IN POTATO-TUBERS DURING DEVELOPMENT, AND WITHIN A SINGLE TUBER ALONG A STOLON-APEX GRADIENT

The metabolism of C-14-sucrose was investigated in different regions o f a growing potato (Solanum tuberosum) tuber attached to the mother pl ant, by injecting high-specific activity [(UC)-C-14]-sucrose into a fi ne channel bored in an otherwise intact tuber. The [(UC)-C-14]-sucrose was metabolised more rapidly in the apical region than in the basal ( stolon) region. Only small, and statistically non-significant, changes were found in the fate of the metabolised label. The activity of sucr ose synthase, other enzymes involved in sucrose and starch metabolism, glycolytic enzymes, and the contents of soluble sugars, UDP-glucose, glycolytic intermediates, and fructose-2,6-bisphosphate were compared along the longitudinal axis of potato tubers. These parameters were al so compared in different tubers harvested from a single plant, and in batches of tubers harvested from mother plants of different ages. Sucr ose synthase decreased 2-4 fold along the longitudinal axis of a tuber from the apical to the basal region. It also decreased 50-fold betwee n tubers from growing mother plants to senescing mother plants. The in dividual tubers from growing mother plants had relatively comparable s ucrose synthase activities, but a 20-fold variation was found in tuber s harvested from a senescent plant. Most other enzymes and metabolites were constant within and between tubers, except the changes of fructo se-2,6-bisphosphate which were parallel to sucrose synthase in most tu bers, and small trends in ADP-glucose pyrophosphorylase, fructokinase, UDP-glucose, and the pyruvate/phosphoenolpyruvate ratio. The sucrose content declined 2-3 fold from the apical to basal region of individua l tubers. However it varied greatly between individual tubers. Glucose showed large and unpredictable changes which did not correlate with s ucrose content, activities of invertases or hexokinase, or any other i nvestigated parameters.