Synthesis of cytokinin glucuronides for the selection of transgenic plant cells

Glucuronide derivatives of the cytokinins benzyladenine (BA3GN) and isopentenyladenine are synthesized for selection of plant cells transformed with a beta-glucuronidase gene releasing active cytokinin which stimulates growth of the transgenic cells. Glucuronide derivatives of cytokinins have been synthesized for use as agents for the selection of plant cells transformed with a β-glucuronidase (GUS) gene. In this selection system, the GUS gene functions as both a selectable, as well as a screenable gene. GUS liberates active cytokinin from inactive cytokinin glucuronides which then stimulates growth and regeneration of the transformed cells. The frequently used cytokinin N 6-benzyladenine was conjugated to glucuronic acid at N-3 or at N-9 but only the former was a substrate for GUS. The glucuronide of isopentenyladenine was also made, by coupling at the N-3. This compound was readily hydrolysed by GUS.