Abstract
Cytokinin (CK) is a plant hormone that plays important roles in many aspects of plant growth and development. There are several type of CKs in nature but at least two CK species, t-zeatin and isopentenyl adenin, are considered to be active forms in Arabidopsis. However much unclear matters still remain about biosynthesis pathway and functions of CK. One of the main reasons making difficult for CK research is lack of tools for molecular biology such as CK deficient mutants or biosynthesis inhibitors. Therefore, we challenged to search for candidates of CK inhibitor. First, we searched for candidates of CK inhibitors using correlation analysis of public microarray database AtCAST. From the result, we focused on Uniconazole (Uni) as a candidate of CK inhibitor. It has been reported that Uni affects amounts of other hormones, Brassinosteroid, Gibberellin and Abscisic acid. After Uni treatment, CK response of each hormone insensitive mutant was suppressed except for a CK insensitive mutant. This result suggested Uni inhibit CK responses independently from other hormones. Next, we investigated the changes of CK and intermediates contents after Uni treatment. CKs contents in downstream of CYP735As were significantly reduced by Uni treatment. In order to examine whether Uni prevents CYP735As activity directly, we carried out an in vitro enzyme assay. As a result, CYP735As activity was suppressed by Uni treatment dose-dependently. Thus, we concluded that Uni inhibits CK biosynthesis.
