Abstract
cis-Zeatin (cZ) is a geometric isomer of trans-zeatin (tZ), a highly-active cytokinin, at a double bond of prenyl side-chain. It is thought that cZ might require conversion into tZ to exert cytokinin activity, because cZ showed fairly-low activity in tobacco callus bioassay, low affinity for Arabidopsis cytokinin receptors, and low accumulation level in Arabidopsis. However, cZ and cZ derivates are highly accumulated in some plant species including rice and maize. Furthermore, a maize cytokinin receptor ZmHK1 showed comparable sensitivity to cZ with tZ in a bacteria system, suggesting direct activity of cZ in vivo. In this study, to investigate importance of cZ in rice, we generated transgenic rice plants in which the metabolism of cZ would be perturbed by ectopic over-expression of cZ-O-glucosyltransferase gene. The over-expression rice plants exhibited some visible abnormalities such as dwarf in aerial parts. Based on the phenotypic analysis and profiling of cytokinin metabolism in the over-expression rice, the importance of cZ in rice will be discussed.
