First published online July 10, 2003; 10.1104/pp.103.023945
Plant Physiology 132:2174-2183 (2003)
© 2003 American Society of Plant Biologists
DEVELOPMENT AND HORMONE ACTION
Overproduction of Cytokinins in Petunia Flowers Transformed with PSAG12-IPT Delays Corolla Senescence and Decreases Sensitivity to Ethylene1
Hsiang Chang,
Michelle L. Jones*,
Gary M. Banowetz and
David G. Clark
Department of Horticulture and Landscape Architecture, Colorado State
University, Fort Collins, Colorado 80523 (H.C.); Department of Horticulture
and Crop Science, Ohio Agricultural Research and Development Center, The Ohio
State University, Wooster, Ohio 44691 (M.L.J.); United States Department of
Agriculture Agricultural Research Service, Corvallis, Oregon 97331 (G.M.B.);
and Department of Environmental Horticulture, University of Florida,
Gainesville, Florida 32611 (D.G.C.)
Plant senescence is regulated by a coordinated genetic program mediated in
part by changes in ethylene, abscisic acid (ABA), and cytokinin content.
Transgenic plants with delayed senescence are useful for studying interactions
between these signaling mechanisms. Expression of ipt, a cytokinin
biosynthetic gene from Agrobacterium tumefaciens, under the control
of the promoter from a senescence-associated gene (SAG12) has been one
approach used to delay senescence. We transformed petunia (Petunia x
hybrida cv V26) with PSAG12-IPT. Two independently transformed
lines with extended flower longevity (I-1-7-22 and I-3-18-34) were used to
study the effects of elevated cytokinin content on ethylene synthesis and
sensitivity and ABA accumulation in petunia corollas. Floral senescence in
these lines was delayed 6 to 10 d relative to wild-type (WT) flowers.
Ipt transcripts increased in abundance after pollination and were
accompanied by increased cytokinin accumulation. Endogenous ethylene
production was induced by pollination in both WT and IPT corollas, but this
increase was delayed in IPT flowers. Flowers from IPT plants were less
sensitive to exogenous ethylene and required longer treatment times to induce
endogenous ethylene production, corolla senescence, and up-regulation of the
senescence-related Cys protease phcp1. Accumulation of ABA, another
hormone regulating flower senescence, was significantly greater in WT
corollas, confirming that floral senescence was delayed in IPT plants. These
results extend our understanding of the hormone interactions that regulate
flower senescence and provide a means of increasing flower longevity.
1 This research was supported by the American Floral Endowment (grant to
M.L.J. and D.G.C.). Salaries and research support were provided in part by
State and Federal funds appropriated to the Ohio Agricultural Research and
Development Center, The Ohio State University. This is journal article number
HCS 02–05.
*
Corresponding author; e-mail
jones.1968{at}osu.edu;
fax 330–263–3887.
Received March 21, 2003;
returned for revision April 11, 2003;
accepted May 13, 2003.
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