SECONDARY METABOLISM IN TISSUE-CULTURES OF THEOBROMA-CACAO

A synthetic medium was developed for the routine subculture of callus and cell suspensions of cocoa. All growth hormones and the coconut milk (CM) supplement of previous media were replaced by indole butyric acid (IBA) and zeatin, at concentrations of 1 mg 1−1 IBA and 0·05 mg 1−1 zeatin for callus and 10 mg 1−1 IBA and 0·5 mg 1−1 zeatin for cell suspension cultures. During the exponential phase of the growth cycle on this medium, the total phenolics in the callus and cell suspensions declined but then increased at onset of the stationary phase and finally declined again with cell senescence. The flavonoid compositions of the callus and cell suspension were similar and much less varied than that of the original intact cotyledon. Both tissue cultures contained epicatechin, leucocyanidins, caffeic and coumaric acids, all of which are thought to act as flavour precursors when in the intact fermented cotyledon. The methylated purines, theobromine and caffeine, could not be detected in the tissue cultures even in the presence of high nitrate levels in the medium. When precursors of theobromine synthesis such as xanthine, hypoxanthine and 7‐methyl‐xanthosine, were fed to the cells, theobromine was formed only when the cells were incubated with 7‐methyl‐xanthosine and a methyl donor, methionine, suggesting that part of the biosynthetic route to theobromine synthesis is still functional in the tissue culture. Copyright © 1979, Wiley Blackwell. All rights reserved