Tropane alkaloids (TAs), especially hyoscyamine and scopolamine, are important precursors for anticholinergic and antispasmodic drugs. Hyoscyamine and scopolamine are currently obtained at commercial scale from hybrid crosses of Duboisia myoporoides x Duboisia leichhardtii plants. In this study, we present a global investigation of localization and organization of TA biosynthesis in a Duboisia myoporoides R. Br. wildtype line. The tissue-specific spatial distribution of TAs within D. myoporoides is presented, including quantification of the TAs littorine, 6-hydroxy hyoscyamine, hyoscyamine, scopolamine, and additionally, hyoscyamine aldehyde as well as scopolamine glucoside. Scopolamine (14.77 ± 5.03 mg g-1), and to a lesser extend hyoscyamine (3.01 ± 1.54 mg g-1) as well as 6-hydroxy hyoscyamine (4.35 ± 1.18 mg g-1) (Fig.1), are accumulated in leaves during plant development with the highest concentration of total TAs detected in six-month old plants. Littorine, an early precursor in TA biosynthesis, was present only in the roots (0.46 ± 0.07 mg g-1). During development, the spatial distribution of all investigated alkaloids changed due to secondary growth in the roots. Gene transcripts involved in early stages of TA biosynthesis, pmt, tr-I, and cyp80f1 were found to be most abundant in the roots. In contrast, the transcript encoding hyoscyamine 6 β - hydroxylase (h6h) was highest in the leaves of three-month old plants. This investigation presents the spatial distribution of biochemical components as well as gene expression profiles of genetic factors known to participate in TA biosynthesis in D. myoporoides. The results of this investigation may aid in future breeding or genetic enhancement strategies aimed at increasing the yields of TAs in these medicinally valuable plant species [1].
Fig. 1: Concentration of various tropane alkaloids (mg/DW) in Duboisia myoporoides roots, stem and leaves
[1] Kohnen, KL et al. 2017: Localization and Organization of Scopolamine Biosynthesis in Duboisia myoporoides R. Br. Plant Cell Physiol; 59:107-118