The Role of Ethylene in Interorgan Signaling during Flower Senescence

The roles of 1-aminocyclopropane-1-carboxylic acid (ACC) and ethylene in interorgan signaling during senescence in orchid (Cymbidium) flowers were investigated. Following application of radiolabeled ACC to the stigma or the rostellum (modified lobe of the stigma), radiolabeled ethylene is produced by all flower parts. In intact flowers as well as in excised central columns, stigma- or rostellum-applied ACC or [alpha]-aminoisobutyric acid were largely immobile. Local treatment of the central column of previously aminoethoxyvinylglycine-treated flowers with either ethylene or 2-chloroethylphosphonic acid (ethephon) rapidly induced emission of ethylene from the petals, showing that ethylene is readily translocated within the flower. Creation of alternative outlets (incisions) in the labellum or the central column significantly delayed the occurrence of senescence symptoms in ACC-treated flowers. The results do not confirm the presumed role of ACC as a signal in interorgan communication during flower senescence. In these flowers, ethylene produced in the stigmatic region following pollination or emasculation serves as a mobile factor responsible for senescence symptoms observed in other flower parts.