Mechanisms of tumor induction in crown gall. I. Production and pathogenicity of spheroplasts of Agrobacterium tumefaciens.

The hypothesis that crown gall tumorigenesis requires the formation of spheroplasts was tested by comparing the tumorinducing ability of populations of both permanent and revertable spheroplasts of Agrobacterium tumefaciens with that of popula tions of the typical rod form of the bacterium. Permanent spheroplasts produced by serial transfers in medium containing 0.005 MD-methionine did not produce tumors in either Kalanchoe or Boston daisy. The efficiency of tumor induction in Kalanchoe stems was lower for glycine-induced revertable spheroplasts than for rod forms. In addition, a progressive decrease in tumorinducing ability, detectable within 30 min after the addition of glycine to bacterial cultures, was also demonstrated in primary pinto-bean leaves by means of the quantitative assay of Lippincott and Heberlein. A study of attenuation among glycinerésistantclones of the crown gall bacterium revealed that the capacity for tumor induction is not lost simultaneously for all hosts. It was also observed that attenuated, glycine-résistant mutants may regain the capacity for tumor production with no detectable change in the level of glycine resistance.