Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2003
Publication Date: 8/31/2003
Citation: CHANG, H., JONES, M.L., BANOWETZ, G.M., CLARK, D.G. OVERPRODUCTION OF CYTOKININS IN PETUNIA FLOWERS TRANSFORMED WITH PSAG12-IPT DELAYS COROLLA SENESCENCE AND DECREASES SENSITIVITY TO ETHYLENE. PLANT PHYSIOLOGY. 2003. v. 132(4). p. 2087-2097. Interpretive Summary: Petunias that have been engineered to produce cytokinins, a group of plant hormones, at a time when they would normally senesce, retain color and health of their petals longer than non-engineered plants. We accomplished this by causing the plants to express the IPT gene, a cytokinin biosynthesis gene, by linking the gene to a gene promoter that is activated when the plant begins to senesce. Flowers from these plants retained healthy-appearing petals 6-10 days longer than wild-type petunias. This work demonstrates a basic principle on the role of cytokinins in flower senescence and will have practical applications in horticulture.
Technical Abstract: 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, under the control of the promoter from a senescence-associated gene (SAG12) is one approach to delay senescence. We transformed Petunia x hybrida >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 9 days relative to wild type (WT) flowers. Ipt transcripts increased in abundance following pollination and were accompanied by increased cytokinin accumulation. Total cytokinins were also elevated in unpollinated IPT corollas. Endogenous ethylene production was induced by pollination in both WT and IPT corollas. The cytokinin content altered patterns of ethylene production in IPT corollas but did not significantly decrease overall rates of production. Flowers from IPT plants were less sensitive to exogenous ethylene and required longer treatment times to induce endogenous ethylene production and corolla senescence. Accumulation of ABA, another component of flower senescence, was significantly greater in WT corollas, confirming that floral senescence was delayed in IPT plants. These results extend our understanding of the interactions between hormonal components that regulate flower senescence and provide a means to improve postproduction quality of ornamentals.