Regulation of cytokinin biosynthesis, compartmentalization and translocation

• Published in: Journal of experimental botany 2008-01, Vol.59 (1), p.75-83
• Main Authors: Hirose, Naoya, Takei, Kentaro, Kuroha, Takeshi, Kamada-Nobusada, Tomoe, Hayashi, Hiroaki, Sakakibara, Hitoshi
• Format: Article
• Language: English
• Subjects: Alkyl and Aryl Transferases - metabolism; Arabidopsis; Biological and medical sciences; Biosynthesis; Cell physiology; Cytokinin; Cytokinins; Cytokinins - biosynthesis; Cytokinins - metabolism; Fundamental and applied biological sciences. Psychology; Gene expression regulation; Ligands; Molecular and cellular biology; Nitrates; nitrogen; Phloem; Plant growth regulators; Plant physiology; Plant roots; Plants; Plants - enzymology; Plants - metabolism; Signal transduction; Signal Transduction - physiology; SPECIAL ISSUE REVIEW PAPER; trans-zeatin; transporter; Xylem
• ISSN: 0022-0957; 1460-2431
• DOI: 10.1093/jxb/erm157

Cytokinins, a group of mobile phytohormones, play an important role in plant growth and development, and their activity is finely controlled by environmental factors in the control of morphogenic and metabolic adaptations. Inorganic nitrogen sources, such as nitrate, are a major factor regulating gene expression of adenosine phosphate-isopentenyltransferase (IPT), a key enzyme of cytokinin biosynthesis. Modulation of IPT and macronutrient transporter gene expression in response to nitrate, sulphate and phosphate, and cytokinin-dependent repression of the transporter genes suggest that cytokinins play a critical role in balancing acquisition and distribution of macronutrients. Biased distribution of trans-zeatin (tZ)-type cytokinins in xylem and N⁶-(Δ²-isopentenyl)adenine (iP)-type cytokinins in phloem saps suggest that, in addition to acting as local signals, cytokinins communicate acropetal and systemic long-distance signals, and that structural side chain variations mediate different biological messages. The compartmentalization of tZ- and iP-type cytokinins implies the involvement of a selective transport system. Recent studies have raised the possibility of subsets of the purine permease family as a transporter of cytokinin nucleobases and equilibrative nucleoside transporters (ENT) for cytokinin nucleosides. These biochemical and transgenic data suggest that AtENT6, an Arabidopsis ENT, could also participate in cytokinin nucleoside transport with a preference for iP riboside in vascular tissue.