Metabolism of ricinine in the castor plant.

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Abstract
The metabolism of the alkaloid ricinine by Ricinus communis was studied using ricinine H3 (I) and ricinine-8-C14 (II). (I) was administer-ed to 26- and 49-day-old castor plants and the ricinine isolated at selected intervals. In the 26-day-old plants, 95% of (I) was degraded in 10 weeks. In the 49-day-old plants 75% of (I) was degraded in 13.5 weeks. Degradation of (I) did not occur in the seeds of the 49-day-old plants. It was demonstrated that ricinine could be transported to the seeds and that in situ synthesis also occurred. (II) was formed by injecting nicotinic acid-7-C14 into 26-day-old plants. After 4 days the maximum incorporation into (II) was reached and in the ensuing 11.5 weeks 90% of (II) was degraded. C14O2 was formed from the catabol-ism of (II), but other degradation products from (I) and (II) were not identified. Ricinine was continuously being synthesized by the plants used in these experiments. An individual castor seed was found to contain about 0.1 [mu]mole of the alkaloid and the mature plant (17 weeks old) about 1.2 mmoles. The highest rate of synthesis was 36 [mu]moles/ day, which occurred at the period just prior to flowering. In postflower-ing plants there was a 60% decrease in the amount of ricinine per g of leaves and stems, but the alkaloid content of the flowers and seeds remained relatively constant on a weight basis. At 20 weeks of age the ricinine in the seed accounted for 75% of the total plant alkaloid.