Borochov, A., Kennedy-Leigh Ctr. for Hort. Res., Faculty of Agriculture, Hebrew Univ. of Jerusalem, P. O. Box 12, Rehovot 76-100, Israel
Spiegelstein, H., Kennedy-Leigh Ctr. for Hort. Res., Faculty of Agriculture, Hebrew Univ. of Jerusalem, P. O. Box 12, Rehovot 76-100, Israel
Philosoph-Hadas, S., Dept. Postharvest Sci. Fresh Produce, ARO, Volcani Center, P. O. Box 6, Bet Dagan 50-250, Israel

Accumulated experimental evidence suggests that the decline in the content of membrane components such as phospholipids (PL), is a key event in flower senescence. This loss of membrane integrity can be modulated by ethylene. The aim of this work was to examine the interrelationship between ethylene and one of the products of PL metabolism, diacylglycerol (DAG), during petunia (Petunia hybrida) flower senescence, DAG's role was studied using phorbol 12-myristate 13-acetate (PMA) which acts similarly in kinase activation. Our results demonstrate for the first time a senescence-related transient increase in the content of DAG in petunia plasma membranes. The climacteric-like ethylene rise associated with petal wilting appeared in petunia flowers well after PL degradation and DAG increase had commenced. The appearance and peak magnitude of the ethylene rise was enhanced or increased, respectively, by PMA treatment, thereby accelerating appearance and magnitude of all senescence parameters assayed. Conversely, suppression of ethylene action by silver thiosulfate (STS) resulted in retardation of flower wilting, as well as in abolishment of the PMA-enhancing effects on senescence. The results suggest an active role for lipid metabolites like DAG in enhancing flower senescence, through regulation of ethylene production and action, or possible activation of kinases. This sequence of events implies that ethylene is a mediator of flower senescence, rather than a trigger of the process.