Tropane alkaloid biosynthesis in Datura innoxia Mill. roots and their differential transport to shoots

Pharmacologically important tropane alkaloids such as hyoscyamine, and scopolamine, are synthesized in the roots of several Solanaceae and also accumulate in their shoots. The tropane alkaloids content in roots of D. innoxia seedlings was almost 3-fold higher than in their shoots. Moreover, scopolamine accounted for 77 % of the total tropane alkaloid content in shoots as compared to only 20 % in roots. All candidate genes in the scopolamine biosynthetic pathway were significantly expressed in D. innoxia mature roots with limited expression in mature leaves. Using exogenous isotopically labeled 2H5 L-phenylalanine, we show here that root tissues, but not detached shoots, readily biosynthesize scopolamine. Tropane alkaloids newly synthesized by roots, and preferentially scopolamine, were further transported to shoots. Our evidence indicates that D. innoxia seedlings have the ability to synthesize tropane alkaloids in their roots and differentially transport them to the shoots.