Postharvest Biology and Technology 23 (2001) 161–166 www.elsevier.com/locate/postharvbio Short communication Efficacy of inhibitors of ethylene binding in improvement of the postharvest characteristics of potted flowering plants Margrethe Serek a,b,*, Edward C. Sisler c a Department of Agricultural Sciences, Horticulture, The Royal Veterinary and Agricultural Uni�ersity, Thor�aldsens�ej 57, 1871 Frederiksberg C, Denmark b Department of Horticulture, Floriculture, Uni�ersity of Hano�er, Herrenhaeuser Str. 2, 30-419 Hanno�er, Germany c Department of Molecular and Structural Biochemistry, North Carolina State Uni�ersity, Raleigh, NC 27695, USA Received 15 December 2000; accepted 7 March 2001 Abstract Pre-treatment of potted plants of Campanula carpatica cultivars Dark Blue and Blue Clips and Schlumbergera truncata cultivar Dark Marie with the volatile ethylene binding inhibitor 1-methylcyclopropene (1-MCP) inhibited the effects of exogenous ethylene (bud abscission and wilting of flowers). In an ethylene-free simulated interior environment, display life of the 1-MCP treated plants was unaffected (Campanula) or slightly greater (Schlumbergera) than that of the controls, although not as good as that of plants pre-treated with the anionic silver thiosulfate complex (STS). Differences in effects of both blockers of ethylene binding sites are discussed. © 2001 Elsevier Science B.V. All rights reserved. Keywords: 1-Methylcyclopropene; 1-MCP; Bud abscission; Campanula carpatica ; Ethylene binding; Flower senescence; Schlum- bergera truncata ; Silver thiosulfate; STS Wu, 1992). Two commercially important crops, Christmas cactus (Schlumbergera truncata) and bellflower (Campanula carpatica) have previously been reported as ethylene sensitive (Cameron and Reid, 1981; Serek and Reid, 1993; Sisler et al., 1999). Exogenously applied ethylene caused rapid and complete drop of flowers and buds of S. truncata and also wilting of flowers of C. carpat- ica. Flowers of both species produce endogenous ethylene when exposed to stress or during natural senescence processes (Cameron and Reid, 1981; Serek 1991; Serek and Reid, 1993). Ethylene 1. Introduction The quality and display life of potted flowering plants are often reduced by the effects of ethylene in the environment or physiological effects such as leaf drop, bud abortion and bud abscission, that are attributed to ethylene (Reid, 1985; Reid and * Corresponding author. Tel.: +45-36283406; fax: +45- 35283400. E-mail address:
[email protected] (M. Serek). 0925-5214/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S0925 -5214 (01 )00109 -0 M. Serek, E.C. Sisler / Posthar�est Biology and Technology 23 (2001) 161–166162 biosynthesis in buds of S. truncata was effec- tively prevented by treatment with aminoethoxyvinylglicine (AVG), an inhibitor of ethylene biosynthesis, but this treatment was not effective in the presence of exogenous ethylene. The best effect in quality improvement has been achieved by spraying plants with an inhibitor of ethylene receptor, the anionic silver thiosulfate complex (STS) (Cameron and Reid, 1981; Serek and Reid, 1993 and Serek, unpublished data). This latter technique has been in widespread commercial use (Fjeld and Moe, 1985), but has been criticized for environmental reasons (Nell, 1992). The use of a heavy metal salt in horticul- ture is a matter for concern and a continuous search for alternative strategies to the use of STS for overcoming ethylene-related problems is necessary. During the last few years, several investiga- tions have been reported on the use of a new environmentally safe compound, 1-MCP, for preventing ethylene effects in ornamental crops (Serek et al., 1994, 1995a,b; Porat et al., 1995b; Sisler and Serek, 1997; Macnish et al., 2000a,b). The compound appears to be non-toxic, binds irreversibly to ethylene binding sites and is ac- tive in relatively low concentrations in the ppb range. We report here the results of tests of the effi- cacy of 1-MCP in preventing ethylene effects on the display quality and shelf life of two potted flowering plants, C. carpatica and S. truncata. 2. Material and methods 2.1. Plant material Potted flowering plants of C. carpatica Dark Blue and Blue Clips and S. truncata Dark Marie at the bud stage were obtained from a commer- cial grower and transported to the experimental greenhouses of the Royal Veterinary and Agri- cultural University in Copenhagen. The condi- tions in the greenhouses were: 18/19°C, 80 �mol m−2 s−1 for 16 h per day, 85�5% relative humidity (RH). One week after transfer to the university greenhouses, the plants of S. truncata at bud stage (10–15 mm) were treated with 1- MCP or STS. C. carpatica plants were treated with 1-MCP at the open flower stage, with STS at the bud stage (‘balloon size’). 2.2. 1-MCP treatment Plants were placed in sealed glass chambers at 21°C and 15 �mol m−2 s−1 artificial light and 0–100 nl l−1 aliquots of 1-MCP (gas phase) were injected inside the chamber (Serek et al., 1994). The chambers remained sealed for 6 h. Treated plants were then exposed to ethylene (at 21°C) or placed in the interior environment for evaluation of shelf life. 2.3. STS treatment Plants were sprayed (30 ml per plant) with a commercial STS solution (Argylene APS, Den- mark) containing 0.1 mM STS. Control and STS-treated plants were held for 6 h in a sealed glass chamber with supplementary light as for the 1-MCP-treated plants, before being exposed to ethylene or placed in the interior environment for evaluation of shelf life. 2.4. Ethylene treatment After 1-MCP and STS treatments, 50% of the plants were enclosed in glass chambers venti- lated (40 l h−1) with air containing 0.5 �l l−1 of ethylene gas (Saltveit, 1978). The ethylene concentration was monitored daily by gas chro- matography. Bud drop, flower longevity and display life of plants were recorded. 2.5. E�aluation in the interior en�ironment For evaluation of commercial shelf life of treated plants, they were placed in a simulated interior environment (IE) at 21°C, 50% RH, 12 h per day of light (15 �mol m−2 s−1) from cool white fluorescent tubes. Display life of plants, longevity of individual flowers, bud drop and number of open flowers per plant were recorded daily. M. Serek, E.C. Sisler / Posthar�est Biology and Technology 23 (2001) 161–166 163 2.6. Statistics Statistical procedures were performed using the PC-SAS software package. Differences between means were determined using orthogonal com- parisons or Student’s t-test. 3. Results 3.1. Effects of 1-MCP, STS and ethylene Untreated plants of both investigated species exposed to 0.5 �l l−1 ethylene rapidly lost their decorative value (Table 1). Within 2–6 days of the initiation of ethylene treatment, most of the buds dropped and all flowers senesced (Table 1). Pre- treatment of the plants with 0.1 mM STS strongly inhibited the effects of ethylene, on both flower senescence and bud abscission. The 1-MCP treat- ment was also significantly better than control in preventing ethylene-mediated bud drop and flower senescence, although the ethylene inhibit- ing effect varied depending on the applied concen- tration of the material. None of the 1-MCP treatments gave protection equal to that of STS treatments. 3.2. Effects on display life S. truncata plants that had been pretreated with 1-MCP and STS had an improved flower longevity and consequently, an extended display life in the IE (Table 2). However, STS increased flower longevity by more than 1 day compared to the 1-MCP treatment. In C. carpatica, flower longevity was affected by 1-MCP only in Blue Clips. Display life of both cultivars was not ex- tended by 1-MCP treatment in the absence of ethylene. On the contrary, STS pretreatment had a beneficial effect on flower opening, display life and flower longevity for both investigated species (Table 2, Fig. 1). 3.3. Effects of 1-MCP concentration Treatment of plants with different concentra- tions of 1-MCP resulted in a wide range of re- sponses to applied ethylene (Table 1). Treatment of C. carpatica plants with all 1-MCP concentra- tions essentially eliminated ethylene-stimulated flower senescence over the 9 days of the ethylene treatment. However, increased concentration of the material did not give additional improvement in flower longevity or plant display life. In Table 1 Plant display life and longevity of individual flowers pretreated with various concentrations of 1-MCP, STS, or aira Plant display life (days) Flower longevity (days)Treatment C. carpatica C. carpaticaC. carpaticaS. truncata C. carpatica (Dark Blue) (Dark Blue)(Dark Marie) (Blue Clips)(Blue Clips) Control 6.1a 2a 4a 1.9a 2.5a 7.2a 7b 9bc 5.6b 6.6b1-MCP 20 nl l−1 10.4a 7b 8.8b 5.2b 6.4b1-MCP 50 nl l−1 6.3b5.2b8.8b1-MCP 100 nl l−1 6.4b13.4b 7.0cSTS 18c 10.2c 10.6c 7.8c a After treatment plants were exposed to 0.5 �l ethylene per litre. Display life was considered terminated when there were no more open flowers remaining on each plant (C. carpatica) or when 60% of buds per plant had dropped (S. truncata). Flower longevity was the mean time between opening and senescence for flowers opened before exposure to ethylene. Numbers followed by different letters in a column are statistically different at P=0.05. M . S erek, E .C . S isler / P osthar�est B iology and T echnology 23 (2001) 161 – 166 164 Table 2 Plant display life and longevity of individual flowers treated with 1-MCP, STS or air, prior to placement in the interior environmenta Flower longevity (days)Plant display life (days)Treatment C. carpatica C. carpaticaS. truncataC. carpaticaC. carpaticaS. truncata (Blue Clips)(Dark Marie) (Dark Marie)(Dark Blue) (Dark Blue)(Blue Clips) 9.0a4.6a20.6a 10.1a13.6a24.1dControl 5.1b 10.3a 11.4b1-MCP 20 nl l−1 24.4cd 13.8a 19.8a 12.7b5.5b 10.1a1-MCP 50 nl l−1 19.8a26.2bc 14.2a 10.1a27.1b 11.4b14.4a 19.4a 5.1b1-MCP 100 nl l−1 6.7c 14.7b 17.1c22.2bSTS 25.2b28.2a a Display life was considered terminated when there were no more open flowers remaining on each plant. Flower longevity was the mean time between opening and senescence for flowers opened before placement in IE (C. carpatica) or for the third open flower per plant (S. truncata). Number followed by different letters in a column are statistically different at P=0.05 M. Serek, E.C. Sisler / Posthar�est Biology and Technology 23 (2001) 161–166 165 Fig. 1. Total number of open flowers per plant of S. truncata ‘Dark Marie’ during storage in an environment room after pretreatment with various concentrations of 1-MCP, STS or air. Source of variation: STS versus control, L***Q*; 1-MCP versus control, Lns Qns; STS versus 1-MCP, L***Qns (ns, ***, * nonsignificant or significant at P=0.001 or 0.05, respec- tively). plants, the minute concentration of 20 nl l−1 prevented ethylene-induced flower senescence and extended plant life two to three times. Increase of the 1-MCP concentration did not give an addi- tional effect, suggesting saturation of the ethylene receptors already at the low concentration of 1- MCP. The effect of STS pretreatment increased flower longevity and plant life 1–1.5 days more than for the 1-MCP pretreatment and in the case of S. truncata plants even when the concentration of 1-MCP was increased up to 100 nl l−1. In S. truncata plants, 1-MCP prevented bud drop as effectively as STS during the first week of ethylene treatment, but after that, protection by STS was more effective. Larger differences in effectiveness of both in- hibitors of ethylene perception appeared during storage of plants in an ethylene-free atmosphere in the interior environment room. After 1-MCP pretreatment, flower longevity in Campanula plants was slightly better than control, but did not result in an extension of the display life of plants. STS extended not only flower longevity, but also plant display life and increased opening of flowers in the ethylene-free environment. Similar results were observed with S. truncata, where both in- hibitors increased plant display life, but STS treat- ment was slightly better than 1-MCP. The differences in effectiveness of both com- pounds in preventing ethylene effects are very intriguing. For several ornamental crops, no dif- ferences were reported (Serek et al., 1994, 1995a). However, in our study STS appears to be more effective for a longer period of time. Sisler and Serek (1997) and Sisler et al. (1999) reported in several studies that 1-MCP blocks ethylene re- sponses for up to 12 days in various plant mate- rial after a single exposure. It is believed that 1-MCP molecules bind irreversibly to ethylene receptors (Serek et al., 1994; Sisler and Serek, 1997) and after pretreatment most of the recep- tors are blocked. However, during further plant development new sites are synthesized (Dervinis et al., 2000; Mu¨ller et al., 2000) and such de novo receptors are not protected by 1-MCP and conse- quently, exposure of plant material to exogenous ethylene can cause senescence symptoms. It ap- S. truncata plants at lower concentrations, the inhibitory effect was less marked, only the 100 nl l−1 treatment was significantly different from the control (Table 1). Treatment of S. truncata plants with 1-MCP improved flower longevity and some of the ap- plied concentrations extended plant display life and improved flower opening during storage in IE (Table 2). Treatment of C. carpatica plants did not inhibit flower senescence of the Dark Blue cultivar, but slightly extended flower longevity of the Blue Clips cultivar. 4. Discussion In our study, we observed a spectacular inhibi- tion of the deleterious effects of exogenous ethyl- ene on potted flowering plants by 1-MCP or STS pretreatment. Both compounds prevented ethyl- ene-induced bud drop in S. truncata plants and extended flower longevity and display life of C. carpatica plants. Similar results were reported in previous studies with a range of ornamental crops (Cameron and Reid, 1981; Serek and Reid, 1993; Porat et al., 1995a,b; Serek et al., 1994, 1995a,b; Sisler et al., 1999; Macnish et al., 2000a,b). For Campanula plants, as for many other flowers or M. Serek, E.C. Sisler / Posthar�est Biology and Technology 23 (2001) 161–166166 pears that silver ion remains in the plant tissue for a longer time and after synthesis of new sites, continuously inactivates ethylene responses. A theoretical model for anti-ethylene effects of STS has been suggested by Veen (1986), although the exact mode of silver ion action is still unknown. We can conclude that 1-MCP is an effective blocker of ethylene perception in the investigated species of potted flowering plants. 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