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Summary. During studics on the biogenesis of betalains (I) in cactus fruits (Opuntia sp.). DL- dopa-l-[14C] and -Z-[14C]were incorporated into betanin (111) which was obtained radiopure after crystallization. The specific activity remained constant after conversion to betanitlin (IV) and to a neobctanidin derivative (IX) . Reaction of radiobetanin with proline afforded indicaxanthin (V) carrying more than 90% of the radioactivity. Dopa (VI) is thus an efficient precursor for betalamic acid (VIII) but not for cyclodopa (VII) . Decarboxylation of radiobetanidin and radioindicaxanthin showed that the carboxyl group of dopa remained a carboxyl group in the biotransformation to betalaniic acid. It is concludcd that the aromatic ring of dopa is cleavcd and that re-cyclization involving the nitrogen generates the dihydropyridine moiety. Under the same conditions mcvalonic acid, aspartic acid and phenplalanine showed low incorporations.

Summary In 1949 betalains were reported to possibly co‐occur with an anthocyanidin (cyanidin) in Carpobrotus edulis; however, upon re‐examination of this plant, only betalains and leuco‐anthocyanidins were detected. Thus, to date, all evidence indicates that the two classes of plant pigments, betalains and anthocyanins, are mutually exclusive. The detection of betalains in seven species belonging to the family Amaranthaceae and ten species of the Chenopodiaceae are also reported.

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