We have investigated the relative role of auxin and of Agrobacterium rhizogenes T-DNA in the induction of hairy roots. By infecting carrot discs with suitably constructed bacterial strains containing different T-DNA complements, we have shown that both auxin and the presence of T-DNA in the carrot cells are required for root growth on the discs. Auxin added alone or in combination with cytokinin is not sufficient to induce rooting on uninfected discs. Also cells transformed by T-DNA containing only auxin synthetic genes very rarely differentiate into roots. On the other hand auxin is necessary for hairy root induction since A. rhizogenes devoid of T-DNA-borne auxin genes is not capable of eliciting symptoms in the absence of hormone. Auxin is not required for either T-DNA transfer or T-DNA expression in the transformed host. Cells infected in the absence of auxin, which do not respond by rooting, do contain T-DNA whose expression is shown by the synthesis of hairy root opines; subsequent addition of auxin to these quiescent transformed cells results in root development. A model for hairy root induction where the action of T-DNA is envisaged as conferring auxin responsiveness to the transformed cells is discussed. © 1987 Springer-Verlag.
THE ROLE OF AUXIN IN HAIRY ROOT INDUCTION / Maura, Cardarelli; Laura, Spano; Domenico, Mariotti; Mauro, Maria Luisa; M. A., Van Sluyis; Costantino, Paolo. - In: MOLECULAR AND GENERAL GENETICS. - ISSN 0026-8925. - 208:3(1987), pp. 457-463. [10.1007/bf00328139]