Effect of Auxin on Expression of the Isopentenyl Transferase Gene ( ipt) in Transformed Bean ( Phaseolus vulgaris L.) Single-Cell Clones Induced by Agrobacterium tumefaciens C58

Abstract

Summary The effect of auxin on the endogenous cytokinin content and on the expression of isopentenyl transferase gene ( ipt ) was investigated in bean ( Phaseolus vulgaris L. cv. Palgong) tumor single-cell clones induced by Agrobacterium tumefaciens C58. The major endogenous cytokinins of tumor single-cell clones were zeatin and zeatin riboside. Endogenous zeatin and zeatin riboside levels in tumor single-cell clones cultured on an auxin-supplemented medium were reduced by six-fold and eight-fold, respectively, while tumor single-cell clones cultured on the 5.0 μM kinetin-supplemented medium did not exhibit any reduction in the levels of these cytokinins. The mRNAs isolated from normal single-cell clones cultured on 5.0 μM kinetin and 2.5 μM picloram-supplemented medium, from transformed single-cell clones cultured on hormone-free medium, and from transformed single-cell clones cultured on 2.5 μM picloram-supplemented medium, were subjected to Northern blot hybridization. The ipt transcript was not detected in tumor single-cell clones cultured on picloram-supplemented medium, but the ipt mRNA was detected in tumor single-cell clones cultured on hormone-free medium. The amount of ipt mRNA in tumor single-cell clones was found to decrease with time in cultures grown on picloram-supplemented medium. The nopaline synthase gene ( nos ) transcript was detected in the tumor single-cell clones from both culture conditions. It is concluded that picloram regulates the ipt mRNA steady state level, either at the transcriptional level or by affecting ipt mRNA stability.