Plant Physiology Preview
Published on July 10, 2003; 10.1104/pp.103.023945
Received March 21, 2003
Returned for revision April 11, 2003
Accepted May 13, 2003
Overproduction of Cytokinins in Petunia Flowers Transformed with PSAG12-IPT Delays CorollaSenescence and Decreases Sensitivity to Ethylene
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.)
* Corresponding author; email: jones.1968{at}osu.edu.
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.
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