Biosynthesis and function of the nortropanealkaloidscalystegines are not completely elucidated in Solanum tuberosum (potato, Solanaceae). Overexpression of putrescine N-methyltransferase increased N-methylputrescine in leaves and did not alter calystegine accumulation in tubersprouts. Tropinone feeding on tropinone reductase I gene knockdown and overexpression plants proved that tropinone reductase I is a functional tropinone reductase in vivo. When tropinone reductase II expression was suppressed by RNA interference, pseudotropine in tropinone fedleaves and calystegine formation in tubersprouts were severely compromised. Calystegine B2did not inhibitsporegermination of theoomycetePhythophthora infestans.Extracts from tubersprouts showed a strong inhibition of P. infestans spore germination. Cucurbic acid was first detected and quantified in S. tuberosumleaves. Tropinone reduktase-like sequences were identified from theS. tuberosum genome database and analysed for genomic structure and proteine sequence.