Tropane alkaloids -: metabolic response to carbohydrate signal in root cultures of Atropa belladonna

Elevated sucrose enhanced the tropane alkaloid accumulation, in particular of calystegines, in root cultures of Atropa belladonna (A. belladonna). Sucrose, several hexoses and sugar analogues were applied to distinguish the effects of sugars as nutrients versus signals, and to investigate the role of sucrose, monosaccharides, sugar transport, sugar phosphorylation by hexokinase and Ca2+ as part of the sugar sensing and signal transfer processes. Alkaloids were measured and indicated that sugars act as both, carbon sources and as signal compounds in root cultures. Sucrose as intact molecule is required for optimal growth; calystegine accumulation is enhanced by the osmoticum sorbitol, which is partly metabolised. Hexokinase and calcium participate in the signal transduction. Sugar signal pathways interact with effects of phytohormones and light. Auxin, which decreases alkaloid levels by inhibition of putrescine-N-methyl-transferase in presence of sucrose, was shown to enhance alkaloids in combination with sorbitol. Incubation of root cultures in light showed increased growth and alkaloids after 2 weeks, but decreased alkaloids after 4 weeks of illumination. Green chloroplasts developed in the root cortex, but root-anatomy remained unchanged. (C) 2002 Published by Elsevier Science Ireland Ltd.