Mass-spectrometric quantitation of cytokinins in tobacco crown-gall tumours induced by mutated octopine Ti plasmids of Agrobacterium tumefaciens

Expression of the isopentenyl transferase gene is regulated by auxin in transgenic tobacco tissues

The isopentenyl transferase gene (ipt) from Agrobacterium tumefaciens was isolated and introduced, via a disarmed binary vector, into tobacco using the Agrobacterium tumefaciens-mediated gene transfer system. The expression of the ipt gene was monitored by RNA hybridization, western blotting and cytokinin analysis. The addition of auxin to the media rapidly reduced the level of cytokinins in the transgenic tissues and this was associated with a reduction in IPT mRNA and protein levels. It is concluded that the hormone auxin can regulate expression of a gene involved in biosynthesis of the second hormone cytokinin. Although exogenous benzyladenine did not directly affect ipt gene expression, it did antagonize the effect of auxin on levels of cytokinins and IPT mRNA and protein.