572 J. AMER. SOC. HORT. SCI. 119(3):572–577. 1994. J. AMER. SOC. HORT. SCI. 119(3):572–577. 1994. A Volatile Ethylene Inhibitor Improves the Postharvest Life of Potted Roses Margrethe Serek 1 and Michael S. Reid Department of Environmental Horticulture, University of California, Davis, CA 95616 Edward C. Sisler Department of Biochemistry, North Carolina State University, Raleigh, NC 2769 Additional index words. bud abscission, DACP, ethylene binding, flower senescence, STS Abstract. Pretreating ‘Victory Parade’ potted miniature roses (Rosa hybrida L.) with photolyzed diazocyclopentadiene (DACP) inhibited the effects of exogenous ethylene (acceleration of leaf and bud drop). In an ethylene-free simulated interior environment, display life of the treated plants was also greater than that of the controls and similar to that of plants pretreated with the anionic silver thiosulfate complex (STS). DACP caused an increase in the binding constant for ethylene in petals and leaves of ‘Victory Parade’ and ‘Cara Mia’ (a cut-flower rose cultivar). Competitive kinetics for the effects of increasing ethylene concentrations on control and DACP-treated plants are consistent with the hypothesis that the effects of DACP are due to irreversible binding to the ethylene-binding site. relative humidity (RH). At commercial maturity (three to five fully open flowers per plant), the plants were treated with DACP or STS. For ethylene-binding experiments, similar plants or commercially harvested flowers of Rosa hybrida ‘Cara Mia’ were air-freighted to North Carolina, where they were used immediately. DACP treatment. Plants were placed in sealed glass chambers at 20C, and calculated aliquots of a 9% solution of DACP in pentane were placed on filter papers inside the chamber. The pentane was without effect if DACP was not present. All DACP values are reported as initial gas-phase concentrations of DACP in μl·liter –1 . The chambers remained sealed for 24 h and were con- stantly illuminated with light (70 μmol·m –2 ·s –1 ) from cool-white fluorescent tubes (ACME, Los Angeles). Treated plants were then exposed to ethylene (at 20C) or placed in the interior environment for evaluation of shelf life. STS treatment. Plants were sprayed (25 ml/plant) with a com- mercial STS solution (Argylene APS, Denmark) containing 0.2 mM STS. Control and STS-treated plants were held for 24 h in a sealed glass chamber with supplementary light, as for the DACP-treated plants, before being exposed to ethylene or placed in the interior environment for evaluation of shelf life. Ethylene treatment. After DACP and STS treatments, 50% of the plants was enclosed for 7 days in glass chambers ventilated (40 liters·h –1 ) with air containing 0.6 μl·liter –1 of ethylene gas. The ethylene concentration was monitored daily by gas chromato- graphy. Leaf and bud drop were recorded. To examine the inhibitory action of DACP further, treated plants (1 μl·liter –1 DACP) were placed in glass chambers ventilated (40 liters·h –1 ) with air containing various concentrations of ethyl- ene gas. Leaf and bud drop was evaluated daily. Evaluation in the interior environment. To evaluate commer- cial shelf life, treated plants were placed in a simulated interior environment at 20C, 60% RH, and 12 h per day of light (15 μmol . m –2 ·s –1 ) from cool-white fluorescent tubes. Bud drop, flower number per plant, and the longevity of individual flowers were recorded daily. Binding assays. Petals or leaves were removed from the plant and allowed to stand overnight for wound ethylene to subside. Binding assays were carried out with 2 g miniature rose petals (5 g of ‘Cara Mia’ petals) or 2 g miniature rose leaves (7 g of ‘Cara Mia’ leaves). Samples were exposed to 0.5 μCi of 14 C-ethylene and DACP in 2.5-liter desiccators for 3 h. Other samples were vented Received for publication 4 June 1993. Accepted for publication 14 Sept. 1993. We thank F. Jackson Hills, Peggy Hale, and Carol Adams for advice on data analysis, Linda Dodge for technical assistance, and Nurserymen’s Exchange, Half Moon Bay, for kindly supplying the plants. The experiments were supported by a grant from the Danish Agricultural and Veterinary Research Council (grant no. 13-4549) and supplementary grants from the Foundation of Hofmansgave, the Foundation of Ib Henriksen and the Carlsberg Foundation (MS). The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. 1 Permanent address: The Royal Veterinary and Agricultural Univ., Section for Horticulture, Rolighedsvej 23, 1958 Frederiksberg C., Denmark. To whom reprint requests should be addressed. The quality and display life of potted flowering plants are often reduced by the effects of ethylene in the environment or physi- ological effects, such as leaf drop, bud abortion, and bud abscis- sion, that are attributed to ethylene (Reid, 1985; Reid and Wu, 1992). Improved quality has been achieved by spraying plants with cytokinins (Halevy and Kofranek, 1976; Serek and Andersen, 1993), which reduce ethylene sensitivity (Zacarias and Reid, 1990), or with the anionic silver thiosulfate complex (STS). This latter technique is now in widespread commercial use (Nowak and Rudnicki, 1990), but has been criticized on environmental grounds. The use of a heavy-metal salt in horticulture will always be a matter for concern, and we have continued to search for alternatives to STS for overcoming ethylene-related problems. Sisler and Blan- kenship (1993) reported the ethylene antagonism of diazocyclopentadiene (DACP), a putative photoaffinity label for the ethylene-binding site. This volatile compound has increased the life of cut carnations (Sisler et al., 1993), and we report here a study of its effects on potted flowering crops, for which its volatility would be a major practical advantage. The pronounced beneficial effects of DACP on potted roses that we observed prompted us to investigate its mode of action in more detail, and we report its effects on ethylene binding in potted roses and in a commercial cut-flower rose cultivar. Materials and Methods Plant material. Four-inch potted flowering plants of Rosa hybrida ‘Victory Parade’ were obtained from a commercial grower at the bud stage and transported to the Univ. of California, Davis. The plants were finished in a growth chamber under the following conditions: 22C, 80 μmol·m –2 ·s –1 from 0200 to 2300 HR, and 90%