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Wintersweet (Chimonanthus praecox) is a woody garden plant with fragrant flowers, which blooms in deep winter. The vase life of fresh cut flowers is 8–9 days. We applied ethylene and 1-methylcyclopropene (1-MCP; an ethylene action inhibitor) to test the role of ethylene in flower opening and senescence. In addition, abscisic acid (ABA), gibberellic acid (GA3), two cytokinins, 6-benzylaminopurine (6-BA), and zeatin (ZT) were also applied. The expression pattern of CpSRG1, a senescence-related gene, was analyzed. Ethylene treatment accelerated flower opening and senescence, decreasing vase life by 2.1 days. It also decreased flower break strength, indicating the induction of abscission. 1-MCP slowed opening, delayed senescence, and prolonged vase life by 2.6 days. Ethylene dramatically induced the expression of the CpSRG1 gene, while 1-MCP suppressed it. ZT promoted flower opening and increased vase life by 1.6 days. It suppressed the expression of CpSRG1. 6-BA, GA3, or ABA had no significant effect on flower opening and senescence of wintersweet. Wintersweet (C. praecox) belongs to the Calycantaceae family and is a 2.5to 3.0-m tall deciduous shrub native to China. Wintersweet is a rare ornamental species and has over a thousand-year history of cultivation; as its name indicates, it blooms particularly in winter from late November to March in central, southern, and south-western China. Its unique flowering time and strong fragrance make it one of the most popular ornamental plants in China; it is appreciated as pot plants and cut flowers, and it has a high ornamental and economic value. The shrub has also been introduced into Korea, Japan, Europe, America, and Australia (Zhang and Liu, 1998). However, the vase life of cut wintersweet flowers is relatively short, and this has hindered the further expansion of commercial demand. It is known that plant hormones are implicated in the regulation of flower senescence, andmay have a dramatic effect on the vase life of cut flowers. Research studies have reported that ethylene promoted flower opening and senescence and shorted the vase life of flowers in a wide range of plant species; alternatively, 1-MCP has been used in prolonging cut flower vase life, and is now widely used commercially during transport (Scariot et al., 2014). Other plant hormones have also been studied, such as ABA, which is considered to be a natural promoter of flower senescence (Reid and Chen, 2007). GA3 has also been reported to delay wilting and senescence-associated proteolysis (Eason, 2002). Furthermore, it is known that GA3 acts as an antagonist to ABA or ethylene action, thereby delaying flower senescence (Hunter et al., 2004a, 2004b; L€u et al., 2014). It has also been noted that cytokinins delay petal senescence in both ethylene sensitive and insensitive flowers (Shimizu-Yumoto and Ichimura, 2013; Trivellini et al., 2015). In general, flower senescence is associated with molecular changes in flower senescent organs (Tripathi and Tuteja, 2007). The senescence-related gene 1 (SRG1; encoding a novelmember of the Fe(II)/ascorbate oxidase) is reported to increase in senescent organs of the model plant,Arabidopsis thaliana, hence, it was proposed as a marker for plant senescence (Baerenfaller et al., 2012; Callard et al., 1996; Heyndrickx and Vandepoele, 2012). For example, to evaluate the early stages of leaf senescence in the AtMYBL overexpressing line at the molecular level, the levels of SRG1 were examined by quantitative polymerase chain reaction (qPCR). The transcripts of SRG1 accumulated to higher levels in AtMYBL overexpressing OX1-7 and OX8-6 lines than in wild type and atmybl RNAi ri6-6 and ri25-1 plants (Zhang et al., 2011). In wintersweet, the role of exogenous ethylene in cut flower senescence is still unclear since conflicting results have been reported in the past (Ma et al., 2012; Sheng et al., 1999). The cytokinin 6-BA has been reported to be involved in the postharvest management of cut wintersweet flowers (Guo and He, 2004). Flower development in wintersweet is subject to complex regulation by multiple hormones as shown by transcriptomic data from the wintersweet flower using RNA-Seq (Liu et al., 2014). However, the involvement of hormones in the opening and the senescence of cut wintersweet flowers has not yet been investigated in detail. Our previous research indicated that the expression level of CpSRG1 (SRG1) from wintersweet was significantly high during flower senescence, whereas it was very low at other stages of flower development. The results showed an association with flower senescence (Sui et al., 2012), so it provided us with a useful molecular tool with which to research the senescence of wintersweet. Since a comprehensive analysis of the postharvest effects of plant hormones on cut wintersweet flowers has not yet been reported, we set out to investigate the effects of several hormones on postharvest quality. The applied hormones were ethylene, two cytokinins (ZT and 6-BA), GA3, and ABA. To investigate the role of ethylene on senescence in cut wintersweet flowers, 1-MCP was also used. Furthermore, we detected the expression of the CpSRG1 gene during the different hormone treatments. This work may contribute to find the effective hormone to delay wintersweet cut flowers senescence, which can be used in postharvest handling of cut flower. Material and Methods Plant material. Cut wintersweet, C. praecox cv. Concolor Makino (the local leading cultivar) was collected from an outdoor nursery in Jingguan, Chongqing, China. Wintersweet flower opening stages have been described previously (Sui et al., 2012; Wu and Hu, 1995): stage 1, bud scales loosen; stage 2, flower buds turn green; stage 3, flower buds enlarge and turn yellow; stage 4, fragrance emerges; stage 5, flowers fully open with strong fragrance; stage 6, petals begin withering. In this experiment, we added a stage 7, the complete senescence period at which the petals turned brown, lost turgidity, and shriveled. Cut flowers were considered ornamentally unacceptable when they reached stage 7. Cut branches with 50% buds at stage 3 were harvested and transferred to the laboratory within 1 h. Uniform diameters of 1-year branches with similar rates of buds or flowers were selected, cut to 30 cm in length, and rehydrated in distilled water for 1 h. Each bud at stage 3 was labeled, treated, and observed. The experiments were conducted in a vase life evaluation room at 12 ± 2 C, 70% to 80% relative humidity, and 12-h photoperiod (15 mmol·m·s irradiance) . Received for publication 23 Apr. 2015. Accepted for publication 19 June 2015. This research was supported by the National Natural Science Foundation of China (grant no. 31370698), the Fundamental Research Funds for the Central Universities (XDJK2013A004, XDJK2010C071, and XDJK2015B013). These authors contributed equally to this article. Corresponding author. E-mail: limy@swu.edu.cn. HORTSCIENCE VOL. 50(9) SEPTEMBER 2015 1365 Plant hormone treatments. Hormone concentrations were tested in preliminary experiments and the optimum concentrations were used in this study. The experiments were arranged into two groups. In one group, cut wintersweet flowers were treated with gaseous ethylene and 1-MCP. In another group, cut flowers were placed in vase solutions containing different hormones. Ethylene or 1-MCP treatment: cut flowers were placed in glass bottles with distilled water and sealed in gas-tight chambers for 24 h. Solutions of 10 mL·L ethylene and 1 mL·L 1-MCP were chosen to treat the flowers. An open bottle containing 50 mL 1 M NaOH was placed in the chamber to prevent the accumulation of CO2. Flowers of the control were placed in distilled water and sealed in the same size chambers with air. After 24-h treatments, all the flowers were placed in distilled water and then transferred to the evaluation room for further evaluation or experiments. ZT, 6-BA, GA3, or ABA treatment: cut flowers were continuously held in glass bottles containing 200 mM ZT, 100 mM 6-BA, 200 mM GA3, or 100 mM ABA, respectively. Control flowers were placed in distilled water. Phenotype observations. For each treatment, 45 flowers were used in duplicate. Each flower was defined as an independent sample. After treatment, 15 flowers were randomly chosen for morphological observation. The recording of flower stages was carried out daily based on visual symptoms, following the previously described standard. In addition, photodocumentation was made of the cut flowers. The vase life of each flower was considered as ended at stage 7. Recording of stamen movement was performed at 12-h intervals until the stamens were completely erect and enclosed the pistils. Measurement of flower diameter was conducted daily using vernier caliper based on the maximum width of each flower. Calculation of flower diameter increase rate (FDIR) was based on the following formula: FDIR = (Dn – D0) · 100/D0 where Dn is flower diameter on the Nth day and D0 indicates flower diameter before treatment. Measurement of flower break strength. Flower break strength was measured in cut wintersweet flowers after 6 d of hormone treatment. The flower break strength was quantified using a Chatillon DFS-010 force gauge (AMETEK Test & Calibration Instruments, Hatfield, PA). For each sample, at least 15 flowers were measured. The flower break strength was recorded as the minimum force (in gram equivalents) needed to remove the flower from the stem (Sane et al., 2007). RNA extraction and real-time qPCR analysis. For analysis of gene expression, whole flowers were collected at precisely 0, 12, 24, 36, 48, and 72 h after hormone treatments, then immediately frozen in liquid nitrogen and stored at –80 C. At each occasion, three flowers were collected as biological replicates. Total RNA was extracted from flowers using anRNAprep pure Plant RNAPurification Kit (Tiangen Biotech, Beijing, China) and reverse transcribed into cDNAusing a PrimeScript

Effects of Hormone Treatments on Cut Flower Opening and Senescence in Wintersweet (Chimonanthus praecox)