Ectopic expression of maize knotted1 results in the cytokinin-autotrophic growth of cultured tobacco tissues

The ectopic expression of knotted homologues has cytokinin-like effects on plant morphology. The functional relationship between knotted and cytokinin s was investigated in cultures of leaf tissue established from tobacco (Nic otiana tabacum L. cv. Havana 425) plants transformed with the maize knotted 1 (kn1) gene regulated by cauliflower mosaic virus 35S RNA expression signa ls. In contrast to leaf tissues of untransformed plants, leaf tissues of kn 1 transformants were capable of sustained. cytokinin-autotrophic growth on auxin-containing medium and resembled the tobacco cytokinin-autotrophic mut ants Hl-1 and Hl-2. The concentration of 18 cytokinins was measured in cult ures initiated from leaves of three independent kn1 transformants and the H l-1 and Hl-2 mutants. Although cytokinin contents were variable. the conten t of several cytokinins in kill, Nl-1 and Nl-2 tissue lines was at least 10 -fold higher than that of wild-type tobacco tissues and in the range report ed for other cytokinin-autotrophic tobacco tissues. These results suggest t hat the cytokinin-autotrophic growth of Kn1 lines could result from elevate d steady-state levels of cytokinins.