Possible involvement of abscisic acid in senescence of daylily petals

Daylily flowers (Hemerocallis hybrid, cv. Stella d'Oro) senesce and die aut onomously over a 24 h period after opening. Investigations were performed t o determine some of the mechanisms that lead to death of the petals. The fl owers are insensitive to ethylene, but exogenous ABA prematurely upregulate s events that occur during natural senescence, such as loss of differential membrane permeability, increases in lipid peroxidation and the induction o f proteinase and RNase activities. Furthermore, the same patterns of protei nase and RNase activities appearing on activity gels during natural senesce nce are induced prematurely by ABA. The mRNA profile from ABA-treated, prem aturely senescing petals visualized by differential display shows a high de gree of similarity to the mRNA profile of naturally senescing petals 18 h l ater. In addition, endogenous ABA increases before flower opening and conti nues to increase during petal senescence. An osmotic stress by sorbitol inc reases endogenous levels of ABA and upregulates the same parameters of sene scence as those occurring during natural senescence and after application o f ABA. The mRNA profile from sorbitol-treated, prematurely senescing petals shows a high degree of similarity to mRNA from naturally senescing petals, but somewhat less similarity to mRNA from ABA-treated petals. The possibil ity is discussed that ABA is a constituent of the signal transduction chain leading to programmed cell death of daylily petals.