Hormonal Sensitivity Decreases During the Progression of Flower Senescence in Lilium longifloruma

Although lilies (Lilium sp.) are the fourth sold cut flower in the world, much remains to be discovered about the senescence and post-harvest physiology of these ethylene-insensitive flowers. This study investigated the hormonal regulation of flower senescence in Lilium longiflorum with a focus on the possible changes in sensitivity to phytohormones during the progression of tepal senescence. After characterizing the hormonal profile of L. longiflorum 'White Heaven' tepals from anthesis to complete wilting, we evaluated the changes in hormonal sensitivity during senescence by application of a combination of gibberellins and cytokinins at various times post anthesis. We observed a progressive loss of sensitivity to the hormonal treatment: from an increase of more than 2 days in flower lifespan when applied one day after anthesis, to a complete loss of vase-life prolongation when treated at the fourth day after anthesis or later. These observations were accompanied by various changes in the underlying hormonal contents, especially in the gibberellins and abscisic acid (ABA) profile, which was dependent on the application time. The results not only confirm the role of gibberellins and cytokinins as inhibitors, and ABA as a promoter of senescence, but also reveal a progressive loss in hormonal sensitivity and a hormonal cross-talk during the progression of senescence in tepals of L. longiflorum. We conclude that both hormonal levels and sensitivity modulate the progression of tepal senescence in L. longiflorum.