Initiation of auxin autonomy inNicotiana glutinosacells by the cytokinin-biosynthesis gene fromAgrobacterium tumefaciens

摘要

Agrobacteriacarrying mutations at the auxin-biosynthesizing loci (iaaHandiaaMof the Ti plasmid) induce shoot-forming tumors on many plant species. In some cases, e.g.Nicotiana glutinosaL., tumors induced by such mutant strains exhibit an unorganized and fully autonomous phenotype. These characteristics are stable in culture at both the tissue and cellular level. We demonstrate that the cytokinin-biosynthesis gene (ipt) of the Ti plasmid is responsble for the induction of both auxin and cytokinin autonomy inN. glutinosa. Cloned cell lines carrying aniptgene but lackingiaaHandiaaMare capable of accumulating indole-3-acetic acid. Interestingly, non-transformedN. glutinosatissues exhibit an auxin-requiring phenotype when they are grown on medium supplemented with an exogenous supply of cytokinin. These results strongly indicate that exogenously supplied cytokinin does not mimicallthe effects of the expression of theiptgene in causing the auxin-autonomous growth ofN. glutinosacells.