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Articles

Secretion of Zeatin, Ribosylzeatin, and Ribosyl-1'' -Methylzeatin by Pseudomonas savastanoi¹

Plasmid-Coded Cytokinin Biosynthesis

Department of Agricultural Chemistry, Oregon State University, Corvallis, Oregon 97331, Department of Plant Pathology, University of California, Davis, California 95616

Cytokinin production by strains of the phytopathogenic bacterium Pseudomonas syringae pv savastanoi was measured by immunoaffinity chromatography of the culture medium on immobilized anti-cytokinin antibodies, followed by high performance liquid chromatography, radioimmunoassay and mass spectrometry. P. savastanoi strain PB213-2 secretes zeatin (80 nanograms per milliliter) and ribosylzeatin (80 nanograms per milliliter). Even higher levels of zeatin (400 nanograms per milliliter) are produced by the olive-specific strain EW1006, which also produces 180 nanograms per milliliter of the recently identified cytokinin, ribosyl-1'' -methylzeatin. The amounts secreted were approximately 1000 times greater than those secreted by Agrobacterium tumefaciens (DA Regier, RO Morris 1982 Biochem Biophys Res Commun 104: 1560-1566). Examination of cytokinin production by plasmid deletion mutants of PB213-2 and EW1006 indicated that cytokinin biosynthesis was specified, at least in part, by plasmid-borne genes. A fragment of the 105 kilobase pair plasmid from EW1006 was cloned into Escherichia coli where its expression resulted in dimethylallyl transferase activity and the secretion of zeatin.

¹ Supported by Grants PCM 83-03371 from the National Science Foundation and 83-CRCR-1-1249 from the Competitive Research Grants Office, Science and Education Administration, United States Department of Agriculture. F. R. and N. L. G. supported by fellowships from funds awarded to the University of California, Davis, by the McNight Foundation. Technical Paper No. 7626 from the Oregon State University Agricultural Experiment Station.

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