Incorporation of arginine, ornithine and phenylalanine into tropane alkaloids in suspension-cultured cells and aseptic roots of intact plants of Atropa belladonna
1994
Nyman, S.
Label from U-14C-arginine (Arg), -ornithine (Orn) and -phenylalanine (Phe) was incorporated into hyoscyamine and scopolamine by both dissected roots of intact plants and homogeneous or aggregating suspension cultures of Atropa belladonna L. The early biosynthetic compounds (hygrine, tropinone, tropanol) were found only in the roots, and alkaloid synthesis proceeded as far as to scopolamine there. In the synthesis of the tropane skeleton, Orn was used more efficiently than Arg. Phe was quickly metabolized both in roots and suspension cultures, and the label was incorporated into both ethanol-insoluble compounds, particularly proteins and different ethanol-soluble compounds, especially phenolics. When the callus, used to initiate suspension cultures, was repeatedly subcultured, the degree of organization of the suspension-cultured cells (second suspension passage) grown in the presence of 2.5 micromolar 2-naphthaleneacetic acid (NAA), changed first from homogeneous to aggregating and later to heavily rooty. Simultaneously with an increasing degree of organization, alkaloid synthesis decreased. At first, the rate of incorporation of Arg and Phe, and later Orn into alkaloids decreased. In heavily rooty suspensions neither hyoscyamine nor scopolamine were found, but traces of tropanol were detected. Hence, the synthesis of tropane alkaloids seems to be regulated at the later biosynthetic steps.
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