C. Coenen et Tl. Lomax, THE DIAGEOTROPICA GENE DIFFERENTIALLY AFFECTS AUXIN AND CYTOKININ RESPONSES THROUGHOUT DEVELOPMENT IN TOMATO, Plant physiology, 117(1), 1998, pp. 63-72
The interactions between the plant hormones auxin and cytokinin throug
hout 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 d
iageotropica (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 ro
ot elongation, but cytokinin effects on hypocotyl growth and ethylene
synthesis in these seedlings were not impaired by the dgt mutation. Se
ven-week-old, green wild-type and dgt plants were also equally sensiti
ve to cytokinin with respect to shoot growth and hypocotyl and interno
de 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 mutati
on were again additive. However, although callus induction from dgt hy
pocotyl explants required auxin and cytokinin, dgt calli did not show
the typical concentration-dependent stimulation of growth by either au
xin 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 dg
t mutation, indicating that auxin and cytokinin regulate plant growth
through both shared and separate signaling pathways.