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.

(3,6) to o-ccuir in planits belonging to 10 famiilies which Mabry ct 0i1., (4) stuggested shouild constitute the Order Ccntrosper-

Summary In order to establish the reliability of the betalains as criteria for circumscribing the Centrospermae, taxonomists are requested to forward to the authors one or two voucher specimens of red pigmented species which might belong to the Centrospermae but which are not listed in the table of betalain‐containing species.

No abstract