The cross-reactivity of
antibodies elicited in rabbits against
zeatin riboside, to a wide range of naturally occurring
cytokinins, was examined. As well as to
zeatin riboside, the
antisera cross-reacted to a considerable extent with
zeatin, lupinic
acid, zeatin-9-glucoside,
zeatin riboside 5'-monophosphate and to a much lesser, but measurable extent, with
dihydrozeatin riboside and
dihydrozeatin. Chromatographic methods were devised which allowed separation of all these cross-reactive compounds. Four
biological samples, extracts of immature Zea mays kernels, immature seeds of Lupinus luteus, and Datura innoxia crown gall
tumor tissue, and a sample of Agrobacterium tumefaciens culture supernatant, were purified by these chromatographic methods, using [(3)H]
zeatin riboside as a recovery marker, and at each stage of the purification process, were subjected to radioimmunoassay over a range of dilutions. At each stage of sample purification, sample dilution curves were found to be parallel to the standard curve. Sample
cytokinin levels estimated by radioimmunoassay were in close agreement to those available in the literature for similar samples assayed by alternative methods. However, in some samples, unknown cross-reacting compounds were detected.