Host and T-DNA determinants of cytokinin autonomy in tobacco cells transformed byAgrobacterium tumefaciens.

The hormone autonomy of tobacco (Nicotiana tabacum L.) cells transformed byAgrobacterium tumefaciens containing mutations attmr (the "rooty" locus) of the pTiT37 plasmid has been examined. These cells require cytokinin, but not auxin for continuous growth in culture, indicating that the function of thetmr locus is to specify or induce cytokinin autonomy. Examination of tissues from plants regenerated from cells transformed by the mutant bacteria showed that the auxin independent phenotype is suppressed, but can be reinitiated in culture by exposure to an exogenous supply of auxin. In addition the developmental state of the cells from such regenerated plants can exert a profound influence on their cytokinin autonomy phenotype.