Agrobacterium rhizogenes causes hairy root disease in plants. These hairy roots are genetically stable and grow rapidly. Transformed hairy roots of Hyoscyamus muticus induced by the bacterium can produce tropane alkaloids in trace amounts of intact plant tissues. In this research to compare growth and biosynthetic stability of hairy roots with normal ones, leaf and nodal segments of the plant were inoculated by A. rhizogenes strains A4 and LBA9402. When hairy roots appeared, both normal and transformed roots were cultured in liquid B5 medium. The amounts of tropane alkaloids in both normal and transformed roots were measured by HPLC. The growth rates of transformed roots were stable and their dry weights were four times higher than those of normal roots. Alkaloid content was the same for both transformed roots and normal ones. However, when hairy roots underwent an autonomous dedifferentiation and produced callus, their hyoscyamine content decreased considerably, whereas scopolamine content, not only did not decrease, but also in some cases increased dramatically. A callus producing hairy root clone, produced 2.72 mg/g scopolamine which is a considerable high record for hairy roots of H. muticus.

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