title: Cell-autonomous cytokinin-independent growth of tobacco cells transformed by Agrobacterium tumefaciens strains lacking the cytokinin biosynthesis gene.
abstract: Mutations at the cytokinin biosynthesis locus (tmr) of Agrobacterium tumefaciens usually result in strains that induce tumors exhibiting the rooty phenotype associated with high auxin-to-cytokinin ratios. However, tobacco (Nicotiana tabacum cv Havana 425) leaf disc explants responded to tmr- mutant strain A356 by producing rapidly growing, unorganized tumors, indicating that these lines can grow in a cytokinin-independent fashion despite the absence of a functional tmr gene. Several methods have been used to characterize the physiological and cellular basis of this phenotype. The results indicate that tmr- tumors have a physiologically distinct mechanism for cytokinin-independent growth in comparison to tumors induced by wild-type bacteria. The cytokinin-independent phenotype of the tmr- transformants appears to be cell autonomous in nature: only the transformed cells and their progeny were capable of cytokinin-independent growth. Specifically, the tmr- tumors did not accumulate cytokinin, and clonal analysis indicated the tmr- transformed cells were not capable of stimulating the growth of neighboring nontransformed cells. Finally, the cytokinin-independent phenotype of the tmr- transformants was shown to be cold sensitive, whereas the wild-type tumors exhibited a cold-resistant cytokinin-independent phenotype. Potential mechanisms for this novel form of cytokinin-independent growth, including the role of the dehydrodiconiferyl alcohol glucosides found in both tumor types, are discussed.
authors.affiliation: Biology Department, Pennsylvania State University, Media 19063.
authors.forename: R C
authors.initials: RC
authors.lastname: Black
authors.forename: A N
authors.initials: AN
authors.lastname: Binns
authors.forename: C F
authors.initials: CF
authors.lastname: Chang
authors.forename: D G
authors.initials: DG
authors.lastname: Lynn
mesh_terms: D016960:Agrobacterium tumefaciens / Q000235:genetics*; D002455:Cell Division / Q000187:drug effects; D002461:Cell Line, Transformed; D003583:Cytokinins / Q000096:biosynthesis* / Q000235:genetics / Q000494:pharmacology*; D017353:Gene Deletion; D005798:Genes, Bacterial; D005838:Genotype; D005960:Glucosides / Q000032:analysis / Q000378:metabolism; D008954:Models, Biological; D016296:Mutagenesis; D010641:Phenotype; D010947:Plants, Toxic; D014026:Nicotiana / Q000166:cytology* / Q000187:drug effects
chemical_list: D003583:Cytokinins; D005960:Glucosides; C051457:dehydrodiconiferyl glucoside