Calystegines are polyhydroxylated nortropane alkaloids. In Solanum tuberosum L. calystegine A3, B2, and B4 accumulate in all plant tissues. Calystegines are inhibitors of glycosidases and derive from tropane alkaloid biosynthesis. Enzymes of the biosynthesis (PMT, TRII) were characterized from calystegine forming plants. A central question of this thesis was the physiologically role of calystegines in plants. Potatoes with altered carbohydrate metabolism presented ideal starting material for simultaneous analysis of calystegines and primary metabolites. Potatoes with invertase overexpressed in the apoplastic or in the cytosole and potatoes with suppressed sucrose synthase were analyzed for their calystegine biosynthesis. Calystegines accumulated in tuber peel, in dormant tuber eyes, in tuber sprouts, in roots, and in stolons. Some potato lines with altered carbohydrate metabolism accumulated more calystegines after harvest, during storage, and in potato plants. pmt-transcript was only detected in roots. Transcript, protein, and enzyme activity of TRII was found predominantly in plant tissues except the tuber and in tuber sprouts. Biosynthetic enzymes showed different expression levels in potatoes with altered carbohydrate metabolism. Calystegines A3, B2, and B4 were measured together with primary metabolites by metabolic profiling in tuber sprouts and tuber peel. Calystegine A3 correlated with calystegine B2, but not with calystegine B4. Calystegines A3, B2, and B4 further correlated with the biosynthetic precursor putrescine in tuber sprouts. The hypothesised correlation between calystegines and disaccharides and between calystegines and sugar phosphates were confirmed in sprouts. Application of carbohydrates to isolated potato tissues led to more calystegines. Among those carbohydrate metabolism enzymes that were tested for inhibition by calystegine B2 UDPglucose pyrophosphorylase was not inhibited, but inhibition of phosphoglucomutase was observed.