Figure 2 Chemical structures of scopolamine, camptothecin, and taxol.
tages are the investments and the long lead times required for the establishment of plantations and for responding to changing market demands as well as environmental risks due to adverse weather conditions, pests, and diseases. Also, climatic and soil requirements of the plants to be cultivated have to be taken into account. Examples of medicinal plants that are grown on farms for the purpose of phytochemical production are Pilocarpus microphyllus (pilocarpine), Digitalis lanata (digitalis cardiac glycosides), Papaver somniferum (codeine and morphine), and Duboisia interspecific hybrids (hyoscyamine and scopolamine).
A great deal of progress has been made in the cultivation of plant cells under controlled conditions in bioreactors that can be operated at virtually any geographic location. The low productivity of plant cell cultures regarding secondary metabolites that has often been observed in many cases can be improved significantly by strain selection and elicitation (3,6). As an alternative to plant cell cultures, the use of organ cultures such as fast-
growing hairy root cultures obtained after transformation using Agrobacte-rium rhizogenes has been proposed (7,8): the main location of secondary metabolite biosynthesis is often in the roots, which maintain secondary metabolite production in culture and are genetically stable for long periods of time, in contrast to what has been observed in many plant cell cultures (9). However, the cultivation of organized structures such as hairy roots on a large scale in bioreactors is inherently more difficult than for cell cultures and, thus, has been demonstrated up to the 500 L scale only (10). In contrast, plant cells have been successfully cultivated up to the 60,000 L scale (3). As the costs of large-scale production of phytochemicals using plant cell cultures are still prohibitively high, to date there have been only few examples of their commercial application (2).
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