Some observations on pigment biosynthesis.
Francis, F. J.
Evidence that the synthesis of beta-carotene in maturing Tangerine-type tomatoes could not be formed by the Porter-Lincoln series was obtained by injecting tomatoes with sodium acetate-l-C^l4. The radioactivity count for beta-carotene was much higher than that for the preceding members of the series. The C^14 would only be incorporated into beta-carotene formed in the ripening process, not the carotene already formed in the green tomato, consequently the above conclusion is valid only for the beta-carotene produced in the ripening process.
Indirect evidence favoring a parallel rather than a sequential type synthesis was obtained from a study of the effect of maturation on carotenoid formation in Tangerine tomatoes. All the pigments accumulate at the same time and there is no relative increase in the pigments at the end of the sequence. Further indirect evidence was obtained by infusing diphenylamine, mannitol, beta-ionone and alpha-ionone into red tomatoes containing small quantities of the compounds in the Porter-Lincoln scheme. Lycopene formation was inhibited but the other members of the series do not accumulate. On the other hand, the formation of beta-carotene was either unaffected or increased, indicating that lycopene and beta-carotene are probably synthesized by separate pathways.