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 P SAG12 -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.Flower senescence represents the last stage of floral development and results in wilting or abscission of whole flowers or flower parts (Stead and Van Doorn, 1994). The process, like whole plant senescence, is an active one that is executed via a defined genetic program. Once a flower has been pollinated or is no longer receptive to pollination, the programmed senescence of petals allows for the removal of a metabolically costly tissue whose sole role in sexual reproduction is to attract a pollinator. In many flowers, pollination-induced petal senescence results in the degradation of macromolecules from a structure that is no longer needed and allows for the remobilization of nutrients to developing tissues like the ovary (Stead, 1992).Senescence is accompanied by changes in endogenous ethylene, abscisic acid (ABA), and cytokinins, and these changes are believed to mediate signaling events that control the process. In many flowers, senescence is accompanied by a burst of ethylene production, and treatment with exogenous ethylene accelerates ethylene production and corolla senescence (Borochov and Woodson, 1989). Chemical or genetic inhibition of ethylene biosynthesis or perception also delays flower senescence (Veen, 1979; Fujino et al., 1980;Savin et al., 1995; Wilkinson et al., 1997; Bovy et al., 1999). In ethylene-insensitive plants like daylily, ABA is thought to be the primary horm...