Metabolic links between the biosynthesis of pyrrolizidine alkaloids and polyamines in root cultures of Senecio vulgaris.

Isotope feeding and inhibitor experiments were performed in order to elucidate the pathway common to polyamine and alkaloid biosynthesis in root cultures of Senecio vulgaris L. α-Difluoromethylarginine, a specific inhibitor of arginine decarboxylase, prevented completely the incorporation of radioactivity from [(14)C]arginine and [(14)C]ornithine into spermidine and the pyrrolizidine alkaloid senecionine N-oxide. In contrast, α-difluoromethylornithine, a specific ornithine-decarboxylase inhibitor, had no effect on the flow of radioactivity from labelled ornithine and arginine into polyamines and alkaloids. Thus, putrescine, the common precursor of polyamines and pyrrolizidine alkaloids, is exclusively derived via the arginine-agmatine route. Ornithine is rapidly transformed into arginine. Recycling of the guanido moiety of agmatine back to ornithine can be excluded. Putrescine and spermidine were found to be reversibly interconvertable and to excist in a highly dynamic state. In contrast, senecionine N-oxide did not show any turnover but accumulated as a stable metabolic product. In-vivo evidence is presented that the carbon flow from arginine into the polyamine/alkaloid pathway may be controlled by spermidine. The possible importance of the metabolic coupling of pyrrolizidine-alkaloid biosynthesis to polyamine metabolism is discussed.

Alkaloid patterns and biosynthetic capacity of root cultures from some pyrrolizidine alkaloid producing Senecio species.

Root cultures of Senecio vulgaris, S. vernalis, S. erucifolius and S. squalidus were established. The patterns of pyrrolizidine alkaloids found in these root cultures were analyzed by high-resolution GC and GC-MS and compared with the alkaloids present in the respective plants. In vitro cultured roots produce alkaloid patterns and accumulate quantities which are comparable to those found in soil grown plants. With the exception of the otonecine derivative senkirkine all pyrrolizidines accumulate as N-oxides. Only senkirkine is partially released into the medium. The cultures incorporate biosynthetic precursors, e.g. (14)C-labelled putrescine or spermidine with high efficiency into the alkaloids. Senecionine N-oxide was found to be the main product of biosynthesis. Evidence is presented that senecionine N-oxide is directly transformed into senkirkine, the main alkaloid of S. vernalis root cultures.

Reinvestigation of the Alkaloid Composition of Atropa belladonna Plants, Root Cultures, and Cell Suspension Cultures.

The alkaloid composition of ATROPA BELLADONNA was analyzed by high resolution GLC and GLC-MS. A total of 13 alkaloids, most new for ATROPA, were identified from roots. The aboveground parts of the plant revealed 7 alkaloids; the hygrines were completely absent. The alkaloid pattern of root cultures was almost identical with the pattern of roots from intact plants. The patterns differed only quantitatively. Scopolamine which in A. BELLADONNA seems to be synthesized in the roots only, was preferably excreted into the culture medium. Norhyoscyamine was found frequently in plant shoots. The occurrence of hyoscyamine N-oxide in various plant organs could be confirmed. Cell suspension cultures produced trace amounts of hyoscyamine, 3alpha-acetoxytropane and 3alpha-tigloyloxytropane. The last two ester alkaloids were not detectable in intact plants.