Submitted to: American Society for Horticultural Science
Publication Type: Abstract Only
Publication Acceptance Date: 4/30/2003
Publication Date: 4/30/2003
Citation: JONES, M.L., BANOWETZ, G.M. ELEVATED CYTOKININ LEVELS IN SAG12-IPT PETUNIAS DELAY FLOWER SENESCENCE AND DECREASE SENSITIVITY TO ETHYLENE. AMERICAN SOCIETY FOR HORTICULTURAL SCIENCE. 2003. Interpretive Summary: Flower senescence which results in wilting and loss of color to ornamental flowers, is regulated by changes in plant hormone concentrations and sensitivity of floral tissues to specific hormones. Petunias (Petunia x hybrida cv V26) that were modified by insertion of a gene, ipt, that causes production of cytokinins, hormones that keep plants green, were used to study how different hormones regulate senescence. The gene that was inserted into these petunias caused cytokinin production at a time when normal plants were beginning to senescence. Turning on the gene at this time caused floral senescence in these plants to be delayed 6 to 10 days relative to normal flowers. We measured the amounts of cytokinins that caused this to happen and showed that production of cytokinin at this time reduced the sensitivity of the flowers to ethylene, a plant hormone that causes plants to senescence. These results increase our knowledge of the interactions between hormones that regulate flower senescence and this work also provides a means to extend the useful life of cut blooms and improve postproduction quality of ornamental flowers.
Technical Abstract: Flower senescence is regulated by a coordinated genetic program mediated in part by changes in endogenous hormone concentrations and tissue sensitivity. Petunias (Petunia x hybrida cv V26) transformed with the cytokinin biosynthetic gene, ipt, under the control of the senescence-associated promoter (SAG12) were utilized to study the hormonal regulation of senescence. Floral senescence in SAG12-ipt plants was delayed 6 to 10 days relative to wild type flowers. Flowers of SAG12-ipt plants accumulated primarily zeatin and zeatin riboside, and the largest accumulation of cytokinins in SAG12-ipt corollas was detected at 48 hours after pollination when wild type corollas were senescent (petals wilted and starting to brown). Pollination induced endogenous ethylene production from both wild type and SAG12-ipt corollas, but this ethylene production was delayed in the SAG12:ipt flowers. Flowers from SAG12-ipt plants were also less sensitive to exogenous ethylene and required longer treatment times to induce endogenous ethylene production and corolla senescence. The loss of differential membrane permeability and increases in protease activity often associated with the later stages of flower senescence were also delayed in SAG12-ipt flowers. 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.