Activation of genes presumed in cytokinin signal pathway of two-component system in response to the increased cytokinin contents in ipt-GUS transgenic Arabidopsis.

The ipt-GUS activated transgenic Arabidopsis had 20-25 fold higher cytokinin contents than the wild type. Changes in cytokinin content in vivo triggering gene expressions involved in signal pathway of two-component system have been analyzed on the day of 6 d, 12 d, 20 d and 30 d after seed cultivation on MS medium in light conditions. The results showed that the two cytokinin receptors, His-kinase CRE1 was more sensitive to the increased cytokinin contents than CKI1. Arabidopsis response regulators, ARR4 and ARR5, were induced by the increased cytokinin contents at different time after seed germination. ARR4 responded to cytokinins at early time of seed germination, especially on the 6 d when seedlings were around true leaf initiation, while cytokinins induced ARR5 activation after 6 d of seed cultivation in light conditions, an obvious increase was on the 20 d when seedlings were around inflorescent shoot initiation. Hpt-type transmitter kinase AHP4 increased its activation by cytokinin induction only between the 20 d and 30 d after seed cultivation in light conditions, and an obvious increase was on the 20 d.