Abstract
Isopentenyladenine (iP) nucleotides, which is synthesized by isopentenyltransferase (IPT), are hydroxylated to trans-zeatin (tZ) nucleotides by a cytochrome P450 monooxygenase. The cytokinin (CK) hydroxylase had been supposed to be constitutively expressed because of the predominant accumulation of tZ-type CKs in transgenic plants overexpressing bacterial IPT. Isolation and expression analysis of CYP735A1 and CYP735A2 genes encoding CK hydroxylase in Arabidopsis revealed that the expression was organ specific and regulated by phytohormones, such as auxin, ABA and CK. These results suggested that CK metabolism might be regulated at the hydroxylation step. To identify the tissues or cells expressing CK hydroxylase genes, we generated transgenic Arabidopsis lines expressing GUS or GFP gene controlled by the promoter of CYP735As. We will also discuss the possibility of a long-range transport of CKs via xylem vessels comparing expression site of AtIPTs and CYP735As.
