Introduction Floral life span depends on the fate of the petals. In several species the end of floral life span is due to petal withering or wilting. The petals in most of these species desiccate, and finally abscise or fall due to growth of the fruit. Only in a few species the desiccated petals remain attached to the fruit. In another large group of species the end of floral life span is determined by abscission of petals that are mostly or fully turgid. 2003 1970a b 1970a b 2003 2001 2003 2003 2003 2006a b 2006a b Prunus yedoensis Delphinium belladonna Materials and methods Plant material P. yedoensis D. belladonna Ipomoea nil Petunia hybrida P. yedoensis −2 −1 DNA degradation 2003 2006b Two biological replications, each containing several petals, were used for each stage of development. Depending on the species, two to several petals were used in each sample. Flow cytometry The petal was chopped in nuclear extraction buffer, part of the kit (High Resolution kit) for plant DNA analysis (Partec, Münster, Germany), a reagent set provided by the manufacturer of the flow cytometer used (Ploidy Analyzer, Partec). The extraction buffer in this kit was a low pH solution containing Triton X-100. The extract was filtered through 50 μm nylon mesh. The medium with the isolated DNA masses (nuclei) was collected, the buffer with the fluorescent DNA stain 4, 6-diamidino-2-phenylindole (DAPI) from a standard reagent set (Partec) was added, and the solution was vortex mixed. The DNA content of the isolated nuclei was analysed using the flow cytometer. The flow cytometer apparatus can be set to count all nuclei in a sample, and can be set to analyse a fixed number of nuclei. We here set it to detect 5,000 nuclei. DNA levels were obtained in a total of 5,000 nuclei. It should be noted that the large histogram peak was adjusted to 10 on the fluorescence scale. This means that nuclear condensation was not taken into account in the flow cytometry data. Two biological replications, each containing several petals, were used for each stage of development. Depending on the species, three to several petals were used in each sample. In each species, the number of petals was the same at all stages of development. Nuclear morphology; chromatin condensation Nuclei were isolated from petals in the same way as for flow cytometry. Isolated nuclei were stained with DAPI, which stains DNA. The nuclei were observed under a fluorescence microscope (model PROVIS AX70, Olympus, Tokyo, Japan) using U-excitation (330–385 nm). Digital photography of nuclei was obtained for each stain using low light cool CCD camera (model DP30BW, Olympus). Dehydration and ethylene treatment Flowers were excised when the petals were fully open. Cut flowers were placed in air in the growth chamber (24°C, about 70% RH) or in a desiccator (at 60°C). For ethylene treatments, stems of cut flowers were placed in sterile distilled water, in a closed 70 l clear plastic box containing 2 μl/l ethylene. Petal abscission was checked at hourly intervals and abscised petals were collected immediately. The petals were then used instantly for the measurement of the various parameters mentioned. Statistics P  Results Symptoms of petal life span cessation P. yedoensis 1 1 1 1 Fig. 1 P. yedoensis P a D. belladonna D b P. yedoensis D. belladonna . n P1 D1 P2 D2 P3 D3 P4 D4  Delphinium D. belladonna 1 1 1 1 DNA degradation 2 2 P. yedoensis P  2 D. belladonna 2 P. yedoensis 2 D. belladonna 2 2 Fig. 2 P. yedoensis P a  D. belladonna D b P1 P4 SD1 SD4 P1 P4 D1 D4 1 P1 D1 P2 D2 P3 D3 P4 D4  Nuclear morphology P. yedoensis 3 D. belladonna D. belladonna 3 Fig. 3 P. yedoensis P a D. belladonna D b a b 1 P1 D1 P2 D2 P3 D3 P4 D4  3 P. yedoensis 3 D. belladonna 3 3 3 Flow cytometry of nuclei at various stages prior to and after abscission X 4 Y P. yedoensis 1 X 4 4 Fig. 4 P. yedoensis P a D. belladonna D b Prunus Delphinium 1 P1 D1 P2 D2 P3 D3 P4 D4  D. belladonna 4 4 Effects of ethylene 5 1 5 1 D. belladonna Fig. 5 P. yedoensis D. belladonna a b P. yedoensis D. belladonna. E 1 4 a  EP2 ED2 n P1 D1 EP2 ED2 EP3 ED3 EP4 ED4  5 P. yedoensis 5 4 5 4 D. belladonna. P. yedoensis 5 5 Dehydration of petals cut at flower opening Flowers were harvested just after opening and subjected to a dehydration treatment at 60°C for 24 h. The treatment resulted in a petal FW of about 20% of that of controls. Preliminary experiments showed that such a treatment resulted in a decrease of FW, and in changes of other parameters such as DNA degradation and nuclear morphology, that were very similar to dehydration on the laboratory bench (about 20°C and 70% RH) for about 96 h. P. yedoensis 6 6 D. belladonna 6 Fig. 6 P. yedoensis P D. belladonna D DP DD a P1 D1 DP DD P. yedoensis P1 DP D. belladonna D1 DD b c d DP  DD P1 DP D1 DD  P. yedoensis 6 6 D. belladonna 6 6 P. yedoensis D. belladonna 6 6 3 6 Ipomoea Petunia I. nil Petunia hybrida I. nil 7 P. hybrida 7 Fig. 7 I. nil P. hybrida a n a b c, d DAPI I. nil c P. hybrida d Ip Pe D  7 Ipomoea Ipomoea 7 7 Petunia 7 I. nil P. hybrida 8  I. nil 8 P. hybrida 8 8 Fig. 8 I. nil P. hybrida I. nil a P. hybrida b Ipomoea Petunia 2006a b S1 S2 S3 S4  I. nil 8 P. hybrida 8 Discussion 2003 2006a b D. belladonna P. yedoensis 1997 2001 2 D. belladonna P. yedoensis 4 Ipomoea 1970a b Iris 2003 2005 Alstroemeria 2003 2002 1997 2003 2003 2003 D. belladonna P. yedoensis D. belladonna P. yedoensis 3 2003 Ipomoea 2 4 2 D. belladonna P. yedoensis I. nil P. hybrida P. yedoensis D. belladonna I. nil P. hybrida Ipomoea 2006b Petunia 2006a D. belladonna P. yedoensis