Radioimmunoassay for the Determination of the Indole Alkaloid Vindoline in Catharanthus

Abstract

A radioimmunoassay for the quantitation of the indole alkaloid vindoline has been developed. Antisera produced against a conjugate between desacetyl vindoline glutarate and γ-globulin fraction of bovine serum yielded antibodies which showed a high affinity (K, = 1.66 × 10 ^-10 M) for vindoline and neglegible cross reactivity with other naturally occurring or semisynthetic indole alkaloids. The assay is sensitive and the measuring range is from 0.5-100 pmol (0.2-45 ng) of vindoline. The detection limit is 110 fmol (5 × 10^-11g) and assay reproducibility is high, as shown by a variation coefficient of ca. 2 %. Several hundred quantitative assays can be performed in one day per person, and due to the high specificity of this assay crude extracts may be used for the test. The distribution of vindoline in a single Catharanthus plant and different Catharanthus species as well as in a C.roseus population is given. No evidence was found for the previously claimed cell free formation of vindoline. The radioimmunoassay developed here should prove a valuable tool for the breeding of plants with maximal vindoline content, and also for studies with cell cultures as well as biosynthetic work.