Our previous results demonstrated that endogenous
cytokinins are involved in the shooty potential of
tumors initiated on Eucalyptus globulus plantlets inoculated with Agrobacterium tumefaciens strain 82.139 [A. Azmi et al. (1997a) Plant Sci 127: 81-90]. In order to investigate whether or not these
hormones are distributed homogeneously in the
tumors prior to the onset of bud regeneration, decapitated hypocotyls were inoculated with the strain C58pMP90/T139 GUS-INT harboring the wild transferred
DNA (
T-DNA) of strain 82.139 tagged with the
beta-glucuronidase (gus)-reporter gene. In situ immunolocalization of
zeatin,
dihydrozeatin and
isopentenyladenine was performed in the developing
tumors and combined with the histo-enzymological
beta-glucuronidase assay. It was found that the expression of the
T-DNA was restricted to only some small areas located deeply in the
tumors. These sites were also provided with a high
cytokinin signal while the untransformed parts of the
tumors displayed a weaker signal, except in the early differentiating tracheary elements. The regenerated buds were untransformed and originated from superficial parts of the
tumors provided with a moderate signal for
cytokinins. The method of colocalization of both
cytokinins and gus expression developed here might be helpful for further studies concerning the role of these
hormones in controlling gene expression at cell and tissue levels.