Hormone Synthetic Pathways and Genes in Arabidopsis: Cytokinin

Cytokinins (CKs) are a group of phytohormones that are involved in a wide variety of plant growth and development processes, such as delay of senescence, root proliferation, apical dominance, nutritional signaling and shoot meristem function. Naturally occurring CKs are adenine derivatives that carry either an isoprene-derived side chain or an aromatic side chain at the N6-terminus, called isoprenoid CKs or aromatic CKs, respectively. Because isoprenoid CKs are commonly found in higher plants and are much more abundant than aromatic ones, the metabolic pathway for the isoprenoid CKs has been studied with great intensity. On the other hand, the biosynthetic pathway for the aromatic CKs has not been elucidated, even though these forms of CKs are found in some higher plants, mosses and unicellular algae. The major CK biosynthesis pathway in Arabidopsis is shown here.