Plants represent an unlimited source of natural products. Many of the recently detected phytochemicals exhibit remarkable bioactivities, ranging from anticancer activity, phosphodiesterase inhibition to cytotoxicity against HIVinfected cells. Cultivated plant cells produce at their unorganized, dedifferentiated stage secondary metabolites, but in very different amounts in so far as new compounds are concerned. In fact, more than 140 novel natural products are presently known from plant cell cultures, which also include new metabolites formed by biotransformation. The biotransformation capacity of suspended cells is described and recent high yielding transformations, like the formation of arbutin by hydroquinone-transformation with Rauwolfia cells are discussed. As an example of alkaloid production by cell suspensions, the pattern of monoterpenoid indole alkaloids of the Indian medicinal plant Rauwolfia serpentina Benth. is described and the so far 30 identified compounds are divided into eight groups which are biosynthetically closely related. Some of the key biosynthetic reactions leading to the Rauwolfia alkaloids are discussed and an overview of the enzymes involved in the formation of the alkaloid ajmaline and proteins catalyzing side reactions of the ajmaline pathway are given.

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