Cytokinin Metabolism in Phaseolus Embryos

The metabolism of trans-[8-(14)C]zeatin was examined in embryos of Phaseolus vulgaris cv Great Northern (GN) and P. lunatus cv Kingston (K) in an attempt to detect genetic variations in organized plant tissues. Metabolites were fractionated by HPLC, and identified by chemical and enzymic tests and GC-MS analyses. Five major metabolites were recovered from P. vulgaris embryo extracts: ribosylzeatin, ribosylzeatin 5'-monophosphate, an O-glucoside of ribosylzeatin, and two novel metabolites, designated as I and II. Based on results of degradation tests and GC-MS analyses, I and II were tentatively identified as O-ribosyl derivatives of zeatin and ribosylzeatin. In embryos of P. lunatus, however, metabolites I and II were not present. The major metabolites were ribosylzeatin, ribosylzeatin 5'-monophosphate, and the O-glucosyl derivatives of zeatin and ribosylzeatin. The zeatin metabolites recovered were the same for embryos of different sizes but their quantities varied with embryo size and incubation time. The genetic differences appear to be embryo-specific and may be useful in the studies of the possible relationship between abnormal interspecific hybrid embryo growth and hormonal derangement in Phaseolus. In addition, analyses of both organized (intact) and unorganized (callus) tissues of the same genotype may provide an opportunity to address the problem of differential expression of genes regulating cytokinin metabolism during plant development.