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The Diageotropica Gene Differentially Affects Auxin
and Cytokinin Responses throughout Development in Tomato1
Catharina Coenen2 and
Terri L. Lomax*
Department of Botany and Plant Pathology and Center for Gene
Research and Biotechnology, Oregon State University, Corvallis,
Oregon 97331-2902
The
interactions between the plant hormones auxin and cytokinin throughout
plant development are complex, and genetic investigations of the
interdependency of auxin and cytokinin signaling have been limited. We
have characterized the cytokinin sensitivity of the auxin-resistant
diageotropica (dgt) mutant of tomato
(Lycopersicon esculentum Mill.) in a range of auxin- and
cytokinin-regulated responses. Intact, etiolated dgt
seedlings showed cross-resistance to cytokinin with respect to root
elongation, but cytokinin effects on hypocotyl growth and ethylene
synthesis in these seedlings were not impaired by the
dgt mutation. Seven-week-old, green wild-type and
dgt plants were also equally sensitive to cytokinin with
respect to shoot growth and hypocotyl and internode elongation. The
effects of cytokinin and the dgt mutation on these
processes appeared additive. In tissue culture organ regeneration from
dgt hypocotyl explants showed reduced sensitivity to
auxin but normal sensitivity to cytokinin, and the effects of cytokinin
and the mutation were again additive. However, although callus
induction from dgt hypocotyl explants required auxin and
cytokinin, dgt calli did not show the typical
concentration-dependent stimulation of growth by either auxin or
cytokinin observed in wild-type calli. Cross-resistance of the
dgt mutant to cytokinin thus was found to be limited to a small subset of auxin- and cytokinin-regulated growth processes affected by the dgt mutation, indicating that auxin and
cytokinin regulate plant growth through both shared and separate
signaling pathways.
1
This work was supported by the National Science
Foundation (grants no. BIR-9314619 and IBN-9423651).
2
Present address: Institut für Biologie
II-Zellbiologie, Albert-Ludwigs Universität Freiburg,
Schänzlestrasse 1, D-79104 Freiburg, Germany.
*
Corresponding author; e-mail lomaxt{at}bcc.orst.edu; fax
1-541-737-3573.
Plant Physiol. (1998) 117: 63-72
Copyright Clearance Center: 0032-0889/98/117/0063/10
© 1998 American Society of Plant Physiologists
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