Accumulation and biosynthesis of calystegines in potato.

Calystegines are nortropane alkaloids with glycosidase inhibitory activity. They were determined in tuber tissues and in other plant organs of potato (Solanum tuberosum). Calystegine concentrations in other Solanaceae are given for comparison, the accumulation varies dependent on the Solanaceae species, on the plant organ and the growth stage. The biosynthesis of calystegines is assumed to be a side branch of the tropane alkaloid pathway. The stereospecific reduction of tropinone was identified as a branching point in those plants that accumulate both calystegines and tropine ester alkaloids. Pseudotropine forming tropinone reduction is the putative start of calystegine biosynthesis. The cDNA of the respective tropinone reductase from Solanum tuberosum was isolated, cloned and sequenced. The nucleotide and amino acid sequences show high similarity to other tropinone reductases from Solanaceae. The subsequent biosynthetic steps leading from pseudotropine to calystegines are under investigation, and we aim to understand the physiological and ecological significance of calystegine accumulation.