T-DNA organization in homogeneous and heterogeneous octopine-type crown gall tissues of Nicotiana tabacum.

Octopine-type tumor tissue was obtained both by infection of plants or isolated protoplasts with Agrobacterium tumefaciens and by somatic hybridization of normal and crown gall tobacco cells. Analysis of T-DNA by Southern blotting of clones and uncloned tissue reveals that, whereas tumors induced on plants are heterogeneous mixtures of cells differing in T-DNA organization, each tissue derived from transformed protoplasts or from somatic hybridization is homogeneous. Detailed analysis of T-DNA organization showed that TL- or "core" T-DNA was always present at one or two copies per diploid genome. However, sometimes it was present in a modified form, either deleted, extended, tandemly duplicated or probably methylated. TR-DNA was not detected. The observed variation in the organization of T-DNA in octopine crown gall tissue did not appear to be a characteristic of the way the tissue was derived.