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Plant Physiol, December 2000, Vol. 124, pp. 1718-1727
STUNTED PLANT 1 Mediates Effects of Cytokinin,
But Not of Auxin, on Cell Division and Expansion in the Root of
Arabidopsis1
Gerrit T.S.
Beemster2 and
Tobias I.
Baskin*
Division of Biological Sciences, University of Missouri, Columbia
Missouri, 65211-7400
Plants control organ growth rate by adjusting the rate and duration
of cell division and expansion. Surprisingly, there have been few
studies where both parameters have been measured in the same material,
and thus we have little understanding of how division and expansion are
regulated interdependently. We have investigated this regulation in the
root meristem of the stunted plant 1
(stp1) mutation of Arabidopsis, the roots of which
elongate more slowly than those of the wild type and fail to
accelerate. We used a kinematic method to quantify the spatial
distribution of the rate and extent of cell division and expansion, and
we compared stp1 with wild type and with wild type
treated with exogenous cytokinin (1 µM zeatin) or auxin
(30 nM 2,4-dichlorophenoxyacetic acid). All
treatments reduced average cell division rates, which reduced cell
production by the meristem. Auxin lowered root elongation by narrowing
the elongation zone and reducing the time spent by a cell in this zone,
but did not decrease maximal strain rate. In addition, auxin increased
the length of the meristem. In contrast, cytokinin reduced root
elongation by lowering maximal strain rate, but did not change the time
spent by a cell within the elongation zone; also, cytokinin blocked the
increase in length and cell number of the meristem and elongation zone.
The cytokinin-treated wild type phenocopied stp1 in
nearly every detail, supporting the hypothesis that cytokinin affects
root growth via STP1. The opposite effects of auxin and cytokinin
suggest that the balance of these hormones may control the size of the meristem.
1
This project was supported in part by the U.S.
Department of Energy (grant no. 94ER20146 to T.I.B.), which does not
constitute endorsement by that Department of views expressed herein,
and by the U.S. National Science Foundation (grant no. IBN 9817132 to
T.I.B.). G.T.S.B. was supported by a postdoctoral fellowship from the
Molecular Biology Program of the University of Missouri, Columbia.
2
Present address: Genetics Laboratory, Department
of Plant Genetics, Vlaams Instituut voor Biotechnologie,
University of Ghent, B-9000 Ghent, Belgium.
*
Corresponding author; e-mail BaskinT{at}missouri.edu; fax
573-882-0123.
© 2000 American Society of Plant Physiologists
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