Journal Article

Regulation of cytokinin biosynthesis, compartmentalization and translocation

Naoya Hirose, Kentaro Takei, Takeshi Kuroha, Tomoe Kamada-Nobusada, Hiroaki Hayashi and Hitoshi Sakakibara

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 59, issue 1, pages 75-83
Published in print January 2008 | ISSN: 0022-0957
Published online September 2007 | e-ISSN: 1460-2431 | DOI: http://dx.doi.org/10.1093/jxb/erm157
Regulation of cytokinin biosynthesis, compartmentalization and translocation

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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.

Keywords: Cytokinin; nitrogen; phloem; transporter; trans-zeatin; xylem

Journal Article.  4516 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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