Insertion of the transposon Tn5 into the T-region of the
octopine Ti plasmid of Agrobacterium tumefaciens gives rise to crown gall
tumors having altered morphology. Three loci within the
T-DNA that control
tumor morphology have been detected [Garfinkel, D. J., Simpson, R. B., Ream, L. W., White, F. F., Gordon, M. P. & Nester, E. W. (1981) Cell 27, 143-153]. They influence
tumor size (tml), production of roots (tmr), or production of shoots (tms).
Cytokinin and
auxin levels in such mutant
tumors were examined by HPLC/radioimmunoassay and HPLC/fluorescence assay, respectively. Free
indoleacetic acid levels (in pmol/g) were: uninfected tobacco stem tissues, 128; wild-type A348
tumors, 295; tml mutant
tumors, 307; tmr mutant
tumors, 129; and tms mutant
tumors, 70. Average trans-
ribosylzeatin levels were correspondingly: 0.97, 48, 40, 0.54, and 1,400 pmol/g. trans-
Ribosylzeatin/
indoleacetic acid ratios were as high as 24 in shoot-producing
tumors and as low as 0.003 in root-producing
tumors. The evidence strongly suggests that
tumor phytohormone levels are determined by genes in the
T-DNA.