First published online May 22, 2003; 10.1104/pp.102.017707
Plant Physiology 132:1228-1240 (2003)
© 2003 American Society of Plant Biologists
DEVELOPMENT AND HORMONE ACTION
Cytokinin Oxidase Gene Expression in Maize Is Localized to the Vasculature, and Is Induced by Cytokinins, Abscisic Acid, and Abiotic Stress
Norbert Brugière*,
Shuping Jiao,
Sabine Hantke,
Chris Zinselmeier,
Jeffrey A. Roessler,
Xiaomu Niu,
Robert J. Jones and
Jeffrey E. Habben
Pioneer Hi-Bred International, Agronomic Traits, 7250 N.W. 62nd Avenue,
P.O. Box 552, Johnston, Iowa, 50131–0552 (N.B., S.J., S.H., C.Z., X.N.,
J.E.H.); and Department of Agronomy and Plant Genetics, 411 Borlaug Hall, 1991
Upper Buford Circle, University of Minnesota, St. Paul, Minnesota 55108
(J.A.R., R.J.J.)
Cytokinins are hormones that play an essential role in plant growth and
development. The irreversible degradation of cytokinins, catalyzed by
cytokinin oxidase, is an important mechanism by which plants modulate their
cytokinin levels. Cytokinin oxidase has been well characterized biochemically,
but its regulation at the molecular level is not well understood. We isolated
a cytokinin oxidase open reading frame from maize (Zea mays), called
Ckx1, and we used it as a probe in northern and in situ hybridization
experiments. We found that the gene is expressed in a developmental manner in
the kernel, which correlates with cytokinin levels and cytokinin oxidase
activity. In situ hybridization with Ckx1 and transgenic expression
of a transcriptional fusion of the Ckx1 promoter to the
Escherichia coli  -glucuronidase reporter gene revealed that the
gene is expressed in the vascular bundles of kernels, seedling roots, and
coleoptiles. We show that Ckx1 gene expression is inducible in
various organs by synthetic and natural cytokinins. Ckx1 is also
induced by abscisic acid, which may control cytokinin oxidase expression in
the kernel under abiotic stress. We hypothesize that under non-stress
conditions, cytokinin oxidase in maize plays a role in controlling growth and
development via regulation of cytokinin levels transiting in the xylem. In
addition, we suggest that under environmental stress conditions, cytokinin
oxidase gene induction by abscisic acid results in aberrant degradation of
cytokinins therefore impairing normal development.
Article, publication date, and citation information can be found at
www.plantphysiol.org/cgi/doi/10.1104/pp.102.017707.
*
Corresponding author; e-mail
norbert.brugiere{at}pioneer.com;
fax 515–334–4788.
Received November 14, 2002;
returned for revision December 19, 2002;
accepted March 7, 2003.
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