Abstract: Senescing corolla of Four-O′ clock flower (Mirabilis jalapa L. ) was accompanied by a decline in the contents of RNA and protein as well as an increase of free nucleotides and amino acid but with no change in DNA content. SDS-PAGE of proteins showed a gradual reduction in the molecular weight of protein. RNase activity increased obviously but there was no change of DNase activity. Prior to flower wilting the peroxidase activity increased and the rate of ethylene production reached it's the highest level. When isolated corolla lobes were floated on distilled water, RNase activity and ethylene production increased dramatically in a few hours. But if they were floated on cycloheximide solution, the increase of Rnase activity and ethylene production were completely inhibited. Cycloheximide (0.5–1.0 ppm) could extend the longevity of Four-O′clock flower outtings. Electron micrographs showed that starch grain disappeared after flowering. However, no significant disintegration is observed in cell nucleus and mitochondria during senescence of corolla.

Key words: Mirabilisjalapa , DNA, DNase, RNA, RNase: Protein, Ethylene:cycloHeximide