STUNTED PLANT 1, a gene required for expansion in rapidly elongating but
not in dividing cells, and mediating root growth responses to applied
cytokinin.
Tobias I. Baskin*, Ann Cork, Richard E. Williamson, and Janet R. Gorst
*corresponding author
University of Missouri, Biological Sciences,109 Tucker Hall,Columbia, MO 65211 USA
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fax: 314-882-0123
Plant Physiology, in press.
To understand the control of spatial patterns of expansion,
we studied root growth in wildtype and in the stunted plant 1 mutant,
stp1, ofArabidopsis thaliana. We measured profiles of
cell length and calculatedthe distribution of elongation rate. Slow
growth of stp1 results both froma failure of dividing cell
number to increase, and from low elongation rates in the zone of
rapid expansion. However, elongation of dividing cells was not greatly
affected, and stp1 and wildtype callus grew at identical
rates. Thus, rapid cellular expansion differs in mechanism from expansion
in dividing cells, and is facilitated by the STP1 gene. Additionally,
there was no difference between stp1 and wildtype roots for elongation in
response to abscisic acid, auxin, ethylene, and gibberellin, or for radial
expansion in response to ethylene; however, stp1 responded to cytokinin
much less than wildtype. By contrast, both genotypes responded comparably
to hormones when explants were cultured; in particular, there was no
difference between genotypes in shoot regeneration in response to
cytokinin. Thus, effects on root expansion mediated by cytokinin, but not
effects mediated by other hormones, nor effects on other cytokinin-mediated
responses, require the STP1 locus.