Ethylene production by strains of the plant-pathogenic bacterium Pseudomonas syringae depends upon the presence of indigenous plasmids carrying homologous genes for the ethylene-forming enzyme.

The molecular characteristics of the ethylene-forming enzymes of strains of Pseudomonas syringae were tested. The ethylene-producing activities of the nine strains as measured in vivo and in vitro were similar, except for that of P. syringae pv. mori M5. A polyclonal antibody and a DNA probe for the ethylene-forming enzyme from P. syringae pv. phaseolicola PK2 were prepared to investigate homologies among the proteins and genes for the ethylene-forming enzymes. With the exception of P. syringae pv. mori M5, eight strains tested expressed the same antigen as the ethylene-forming enzyme from P. syringae pv. phaseolicola PK2 and were homologous to DNA sequences on indigenous plasmids. Molecular masses of antigenic proteins from all ethylene-producing strains were 40 kDa. The N-terminal amino acid sequence of the purified ethylene-forming enzyme from P. syringae pv. glycinea KN130 was identical to that of the enzyme from P. syringae pv. phaseolicola PK2. These results show that the ethylene-forming enzymes encoded by the indigenous plasmid(s) in the pathogenic bacteria examined were similar.