5′-Deoxyisopentenyladenosine and other cytokinins in culture filtrates of the bacterium Pantoea agglomerans

A Pantoea agglomerans isolate from barley seeds, selected for inducing growth promotion in tomato test plants, was found to excrete several hormones of the cytokinin class into its culture medium. In addition to isopentenyladenine, isopentenyladenosine and the 2-methylthiol derivates of these, an unknown compound with affinity to anticytokinin antibodies was also isolated. Mass spectroscopy indicated the structure of this to be a deoxyisopentenyladenosine. The structure of 9-(5'-deoxy-beta-D-ribofuranosyl)-6-(3-methyl-2-butenylamino)purine was verified after synthesis of standards and analysis with GC-MS. The synthesized 5'-deoxyisopentenyl-adenosine showed activity in the Amaranthus bioassay, specific for cytokinins. To our knowledge this is the first report of a naturally occurring cytokinin containing 5'-deoxyribose.