Relationships between cytokinin production, presence of plasmids, and fasciation caused by strains of Corynebacterium fascians.

Cytokinin activity in the culture medium of four pathogenic strains of Corynebacterium fascians varied from 168 to 0.4 mug of kinetin (6-furfurylaminopurine) equivalents per liter, as compared to 0.2 in an avirulent control. N(6)-Isopentenyladenine was the predominant cytokinin in the medium of all five strains, and its increased production was correlated with the degree of pathogenicity; however, the virulent strains also produced 8-13 times more cis-zeatin [6-(4-hydroxy-3-methyl-cis-2-butenylamino)purine] than the avirulent strain. The three most virulent strains (with the higher cytokinin contents in the medium) contained a large (M(r) approximately 10(8)) plasmid. The barely virulent strain contained a smaller plasmid. No plasmid was detected in the avirulent control. The total cytokinin content (mole%) and biological activity (mug of kinetin equivalent per mg of tRNA) in tRNA were about the same in all three virulent strains and in the avirulent control. Five cytokinins were isolated from each strain. Four were rigorously characterized as 6-(4-hydroxy-3-methyl-cis-2-butenylamino)-9-beta-D-ribofuranosylpurin e, 6-(3-methyl-2-butenylamino)-9-beta-D-ribofuranosylpurine, and their 2-methylthio derivatives. The fifth cytokinin was tentatively identified as 6-(4-hydroxy-3-methyl-trans-2-butenylamino)-9-beta-D-ribofuranosylpur ine. Ribosyl-cis-zeatin was 3-fold higher and N(6)-isopentenyladenosine was correspondingly lower in the plasmid-containing strains than in the plasmidless control. Because the entire syndrome of fasciation caused by infection can be induced with synthetic cytokinins, the disease would appear to be caused by plasmid-induced high rates of cytokinin production by the bacteria.