Application Of Biotechnology To Duboisia For Scopolamine Production

Boehringer Ingelheim is the major worldwide supplier of the tropane alkaloids hyoscyamine and scopolamine. Scopolamine, which is of higher value than hyoscyamine, is used as a parasymphatolytic and for the production of spasmolytic pharmaceuticals. Previously, the alkaloids were extracted from Datura and Duboisia plants, both belonging to the Solanaceae family. Because of the low content of scopolamine in Datura, extraction of scopolamine from this plant was discontinued in the early 1990s. There are three known species of Duboisia, D. hopwoodii, D. myoporoides, and D. leich-hardtii, all of which are indigenous to Australia (37,38). In a small area in Western Australia, interspecific hybrids between D. myoporoides and D. leichhardtii occur naturally. These hybrids were found to have particularly high levels of scopolamine, with an average content of approximately 1% of leaf dry weight. Commercial cultivation of Duboisia hybrids began during the 1940s, the main area of cultivation being the South Burnett Region in Queensland, Australia (37). The Duboisia hybrids are cultivated in clonal plantations. Figure 4 shows a typical example of a Duboisia plantation plant.

Figure 4 Photograph of a plantation-grown Duboisia hybrid clone in Australia. For harvesting, the plants are usually cut approximately 40 cm above ground. The stem will resprout and the resulting new growth can be harvested again 8 to 12 months later.

A. Conventional Breeding

To improve tropane alkaloid yield, Boehringer Ingelheim started an in-house Duboisia breeding program at Ingelheim during the mid-1970s, based on controlled crosses between superior Duboisia hybrid parents and recurrent selection on an annual basis. During the time period between 1985 and 1991, the resulting improvement in scopolamine content translated into a 40% increase in total scopolamine production from virtually the same annual amount of Duboisia leaf extracted. Additional selection criteria have been tropane alkaloid composition, general growth, leaf density, rooting ability of cuttings, and nematode and insect tolerance. However, insect and nematode damage remains a major problem that severely restricts the productive life of plantation-grown Duboisia plants.

B. Tissue Culture Applications

Micropropagation of Duboisia species is possible using nodal expiants or shoot regeneration from various tissue expiants (39-41) (Fig. 5). Micropropagation techniques can be used for mass propagation of plants and for

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