Abstract
Cytokinins (CKs) are adenine derivatives that carry an isoprene-derived side chain at the N6 terminus. The side chain is modified by hydroxylation, reduction and isomerization. Major CKs in Arabidopsis are isopentenyladenine (iP)-type CKs and trans-zeatin (tZ)-type CKs, which are hydroxylated form of iP-type CKs. This hydroxylation is catalyzed by CYP735A1 and CYP735A2 in Arabidopsis. To clarify the physiological role of the CK hydroxylation, we analyzed insertional mutants of CK hydroxylase genes. In cyp735a1 and cyp735a2 mutants, the amounts of tZ-type CKs were reduced to 80 % of that in WT. In double mutant, cyp735a1/cyp735a2, tZ-type CKs level was lower than 3% of that in WT and iP-type CKs level was twice of that in WT. Reduction of tZ-type CKs affected size of plant and number of rosette branches in double mutant. We are now analyzing mutant phenotype in detail.
