Impaginato 133 Adv. Hort. Sci., 2020 34(2): 133­145 DOI: 10.13128/ahsc­7491 Comparative postharvest responses of carnation and chrysanthemum to syn­ thesized silver nanoparticles (AgNPs) N. Rashidiani 1, F. Nazari 1 (*), T. Javadi 1, S. Samadi 2 1 Department of Horticultural Science, College of Agriculture, University of Kurdistan, Sanandaj, Iran. 2 Department of Chemistry, Faculty of Science, Univesity of Kurdistan, Sanandaj, Iran. Key words: cut flowers, ethylene, microbial growth, silver nanoparticles, vase life, water relations. A b s t r a c t : C a r n a ti o n ( D i a n t h u s c a r y o p h y l l u s L . ) a n d c h r y s a n t h e m u m [Dendranthema grandiflorum (Ramat.) Kitam.] cut flowers are among the most important commodities that dominate flower markets throughout the world. Two major problems in the transportation and marketing of these flowers are their relatively short vase life and the rapid decline of their aesthetic value. In this respect, the current study investigates the effects of silver nanoparticles (AgNPs) on ethylene­sensitive (carnation) and ethylene­insensitive (chrysanthe­ mum) cut flowers. Specifically, this research examines their morpho­physico­ chemical characteristics, antioxidant enzyme activities and vase life. Here, the AgNPs were synthesized by chemical methods and then applied on both flow­ ers by a pulsing method. The treatments involved two concentrations of AgNPs (0.04 and 0.08 g L­1) along with the control (deionized water), and the duration of exposure lasted for 24 h. Then, the flower stems were placed in an aqueous sucrose solution (4%) until the end of the experiment. All traits, except the vase life, were evaluated after 0, 3, 6 and 9 d following the treatments during the vase period. During this time, the control groups of both flowers showed con­ siderable amounts of decrease in the relative fresh weight (RFW), vase solution uptake (VSU), flower diameter, membrane stability index (MSI) and total solu­ ble carbohydrate (TSC). Meanwhile, there were increases in hydrogen peroxide content (H2O2) and peroxidase (POD) activity. The bacterial population of the stem end and total soluble protein (TSP) increased in carnation petals, but decreased in chrysanthemum petals. The activity of superoxide dismutase (SOD) dropped in carnation petals, whereas it rose in chrysanthemum petals. Using AgNPs at concentrations of 0.08 and 0.04 g L­1 can optimally extend the vase life of carnation and chrysanthemum, respectively. 1. Introduction Nowadays, the floriculture industry is one of the most profitable sec­ tors in horticulture. Its financial turnover in all respects amounts to over 300 billion dollars, and one­third of which is related to cut flowers (Chandler and Sanchez, 2012).Consumer demand for cut flowers and (*) Corresponding author: f.nazari@uok.ac.ir Citation: RASHIDIANI N., NAZARI F., JAVADI T., SAMADI S., 2020 ­ Comparative postharvest responses of car‐ nation and chrysanthemum to synthesized silver nanoparticles (AgNPs). ­ Adv. Hort. Sci., 34(2): 133­145 Copyright: © 2020 Rashidiani N., Nazari F., Javadi T., Samadi S. This is an open access, peer reviewed article published by Firenze University Press (http://www.fupress.net/index.php/ahs/) and distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Competing Interests: The authors declare no competing interests. Received for publication 25 November 2019 Accepted for publication 1 April 2020 AHS Advances in Horticultural Science http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ Adv. Hort. Sci., 2020 34(2): 133­145 134 ornamental plants are increasing, and the value of production is inevitably becoming higher. In this regard, flower quality is one of the most important indices in the sale and marketing of cut flowers. This makes flower quality an important factor in attracting customers over and over again (Scariot et al., 2014). Therefore, the advancement of post­harvest pro­ grams is a definite requirement within the cut flower market. Even after their separation from mother plants, cut flowers continue to be metabolically active and proceed with all of their vital processes by consuming the available food in their tissues. Carbohydrates, proteins and fat can be used by cut flowers to meet their metabolic demands. The increase in vase life and the delay in flower senescence can be achieved by upholding the normal rate of water uptake, pre­ venting the depletion of carbohydrate storage and limiting the exposure of flowers to ethylene (Halevy and Mayak, 1981). Water balance is an essential factor in determin­ ing the quality and vase life of flowers. It should be maintained between water uptake and transpiration (Lu et al., 2010). Water uptake can be reduced due to the occlusion phenomenon generated by bacterial accumulation, physiological factors or air embolism (Damunupola and Joyce, 2008). Post­harvest senes­ cence occurs within a few days, and is a major limita­ tion in the marketing of cut carnation and chrysan­ themum flowers. Stem end blockage is one of the important factors in early wilting of leaves and inflo­ rescences in some cut flowers. van Doorn and Vaslier (2002) reported stem blockage is a major factor caus­ ing severe leaf wilting of chrysanthemum. The in­rolling of petal margin and wilting of whole petals in senescence process in some cut flowers (e.g. carnation), is associated with the self­regulation of ethylene production (Yang and Hoffman, 1984), as a hormone, implying that the flowers are sensitive to ethylene. On the other hand, there are flowers such as chrysanthemum, pericallis and narcissus that initi­ ate senescence without being influenced by ethyl­ ene, and thus are considered insensitive to ethylene (Dole and Wilkins, 2005; Jones 2013). Therefore, the short vase life and early wilting of inflorescences of carnation and chrysanthemum may be due to sensi­ tivity of ethylene and stem end blockage, respective­ ly. In fact, in ethylene­sensitive flowers, ethylene is a necessary requirement for the initiation and suste­ nance of senescence­based processes. The mecha­ nisms by which ethylene can stimulate senescence involve changing the cell structure and increasing the concentration of reactive oxygen species (ROSs) such as superoxide radicals, hydroxyl radicals and hydro­ gen peroxide (Abeles et al., 1992). S t u d i e s h a v e a l s o s h o w n t h a t p h y s i o l o g i c a l changes occur during senescence. These include chlorophyll decomposition, decreased activity of antioxidant enzymes, increased productions of ethyl­ ene and ROSs, along with membrane damage to the cells of cut flowers (Prochazkova and Wilhelmova, 2007). Advancements in nanotechnology, especially the development of silver nanoparticles (AgNPs), have led to a wide range of nanocomposites with antimi­ crobial properties. The high surface­to­volume ratio of these particles makes them biologically more active and increases their contact with fungi and bac­ teria (Chau et al., 2007). AgNPs are becoming popular in the flower industry for their ability to inhibit the synthesis of ethylene and delay the senescence in cli­ macteric flowers (Kim et al., 2005). In addition, AgNPs tend to regulate the stomatal aperture, main­ tain the chlorophyll content, preserve the relative fresh weight (RFW) and membrane stability index (MSI), reduce the transpiration rate, weight loss, hydrogen peroxide(H2O2), Malondialdehyde (MDA) and ROSs, and increase the activity of antioxidant enzymes along with their effects on the vase life of different cut flowers such as gerbera (Liu et al., 2009; Solgi et al., 2009; Nazari and Koushesh Saba, 2017), rose (Lu et al., 2010; Nazemi Rafi and Ramezanian, 2013; Hassan et al., 2014), chrysanthemum (Carrillo­ López et al., 2016), carnation (Naing et al., 2017; Lin et al., 2019 b), gladiolus (Li et al., 2017), peony (Zhao et al., 2018) and cut gardenia foliage (Lin et al., 2019 a). The application of AgNPs in vase solution of carna­ tion alleviated vascular occlusion by inhibiting bacter­ ial colonisation and biofilm formation on stem­end cut surfaces and in the xylem vessels (Lin et al., 2019 b). Maity et al. (2019) also showed that the Piper betle silver nanoparticles (PbSNPs) in vase solution of Gladiolus have played an important role for scaveng­ ing ROSs by enhancing antioxidant enzyme activities that led to decrease in MDA and increased the MSI. Nanosponges are new nano­sized colloidal carri­ ers synthesized from ß­cyclodextrins that have been prepared for delivering preservative and anti­ethyl­ ene compounds (Devecchi et al., 2009). Devecchi et al. (2009) evaluated the effect of nanosponges including anti­ethylene molecules, such as 1­methyl­ cyclopropene (1­MCP), 1­methylcyclopentene (1­ MCPt), 2,5­norbornadiene and AgNO3 on vase life of carnation flowers. They concluded that, 1­MCP­ Rashidiani et al. ‐ Silver nanoparticles effects on ethylene sensitive and no sensitive cut flowers 135 nanosponge complex outperformed the other treat­ ments in extending the vase life. In addition, Seglie et al. (2011) reported that 1­MCP in cyclodextrin­based nanosponges improved the vase life of carnation cut flowers. Nonetheless, no report has so far described com­ parisons between the responses of ethylene­insensi­ ti v e a n d e t h y l e n e ­ s e n s i ti v e fl o w e r s t o A g N P s . Therefore, the current research is aimed an evaluat­ ing how the cut flowers of carnation (highly sensitive to ethylene) and chrysanthemum (insensitive or slightly sensitive) respond to the application of AgNPs by the pulsing method. Comparisons are made between the two types of cut flowers by measuring their morphological, physiological and biochemical properties, as well as their enzymatic activities. 2. Materials and Methods Plant materials and application of treatments The cut flowers of carnation (Dianthus caryophyl‐ l u s c v . Y e l l o w V i a n a ) a n d c h r y s a n t h e m u m (Dendranthema grandiflorum cv. Boris Becker Sunny) were harvested at their commercial harvesting stage from a soilless­cultured greenhouse. They were taken to the laboratory and the basal ends of the stems were immediately cut to reduce the stem length to 40 cm. Apart from 3­4 leaves on the top of each stem, all other leaves were removed. Then, AgNPs were applied at two concentrations (0.04 and 0.08 g L­1) by the pulsing method for 24 h. The flowering stems were individually put in a bottle vase contain­ ing 300 mL deionized water. This also contained 4% (w/v) sucrose until the end of the experiment. To prevent the evaporation and contamination of the vase solution, the vase opening was covered with aluminum foil. All traits, except for vase life, were evaluated after 0, 3, 6 and 9 d following the applica­ tion of treatments. The pH of vase solution at the first day (d 0) was 7.82 and 8.76 for carnation and chrysanthemum, respectively. On d 9 of the vase period the pH of vase solution was 3.95 for carnation and 4.06 for chrysanthemum. The pulsing treatments and vase life were evaluated at 23±2°C, 50%±10% RH and 12 h of 15­20µmol m­2s­1irradiance from cool­ white fluorescence lamps. Synthesis of AgNPs To a solution of 0.265 mM (0.045 g) of silver nitrate in 100 mL distilled water, 10 mL of a trisodium citrate aqueous solution (1%) was added slowly at room temperature. After 10 minutes, 0.2 mL of ascorbic acid (0.005 M) was added to the mixture of reaction and stirred for 1 h until a yellow­green AgNPs colloid was formed (Tavallali and Pouresmaeil, 2012). The surface morphology of AgNPs was indicat­ ed by scanning electron microscopy (SEM) (TSCAN, Czech Republic) and showed in figure 1, it is exhibited that AgNPs have a size of about 8­80 nm. Measurement of flower and stem diameter The flower diameter was measured in two direc­ tions, and the stem diameter was measured in three parts (i.e. under peduncle, middle, and end of the stem). These measurements were repeated every three days and the average of values were reported. Measurement of relative fresh weight The relative fresh weight (RFW) of flowering stems in both types of cut flower was calculated every three days by the following formula: RFW (%) = (Wt/Wt0)×100 Fig. 1 ­ The SEM image of AgNPs. Adv. Hort. Sci., 2020 34(2): 133­145 136 where Wt is the weight of the stem (g) at t = d 0, 3, 6, and 9,while the Wt0is the weight of the same stem (g) at t = d 0 (He et al., 2006). Measurement of vase life The vase life of both types of cut flower was mea­ sured by counting the number of days from the beginning of the experiment until 50% of the flower had wilted. In carnations, the occurrence of in­rolling and browning petals by more than one­third was considered as the end of the vase life (Naing et al., 2017). In chrysanthemum, however, the vase life ended when 50% of petals had wilted and the leaves had yellowed (Carrillo­López et al., 2016). Measurement of vase solution uptake The weight of the vase with and without the flower shoots was recorded daily, and the following formula was used for calculating the vase solution uptake (VSU): VSU (mg g­1 stem f. w.) = (St−1­St); where St is the weight of vase solution (g) at t = d 0, 3, 6 and 9, St−1 is the weight of vase solution (g) on the previous day (He et al., 2006; Lu et al., 2010). Measurement of membrane stability index To measure the membrane stability index (MSI) of petals, this method involved the preparation of petal discs (measuring 1 cm in diameter) which were placed in falcons containing 20 mL distilled water. After this, a series of falcons were placed in a warm bath (40°C) for 30 min and their electrical conductivi­ ty (EC) was read by a conductivity meter (C1) after the falcons had cooled down to 25°C. Then, the sec­ ond series of falcons was placed in a warm bath of 100°C for 20 min and their EC was read after having cooled down to 25°C (C2). In the end, the MSI was calculated using the following equation (Sairam et al., 2002): MSI= [1­(C1/C2)] 100 C1 = EC after exposure to 40°C and C2= EC after expo­ sure to 100°C. Measurement of bacterial population of stem end To measure the bacterial population on the stem end, one gram of the stem end was homogenized and diluted with peptone water until a concentration of 10­3was reached. Subsequently, 1 mL of this solu­ tion was transferred to Petri dishes and then a vol­ ume of 10 mL sterilized plate count agar medium was added to each Petri dish. These were slowly mixed for 5 to 10 s. The cultured Petri dishes were then kept in an incubator at 32°C for 2 d and, after count­ ing the bacterial colonies, the results were reported as log CFU g­1 (Balestra et al., 2005; Liu et al., 2009). Measurement of total soluble protein According to the Bradford method (1976), 0.5 g of petal tissue was powdered with liquid nitrogen, and then 0.25 g of polyvinylpyrrolidone (PVP) was added to the solution when stirring the 1.5 mL of potassium phosphate buffer containing sodium metabisulfite (0.019 g per 100 mL buffer). The homogenized sam­ ples were centrifuged (HETTCH, Germany) at 4°C for 20 min at 15,000 g. Then, 50 μL of supernatant was mixed with 950 μL of Bradford solution and, after 15 min, the light absorption was read at 595 nm by a spectrophotometer (UNICO 2100, USA). Measurement of peroxidase activity To measure the peroxidase (POD) enzyme activity, according to a method reported by Hemeda and Klein (1990), first 400 μL of 50 mM potassium phos­ phate buffer (pH 7) was mixed with 40 μL of 1% gly­ col and 40 μL of 0.3% hydrogen peroxide in an ice bed. Then immediately, 65 μL of protein extract was added to the mentioned composition. The changes in light absorption were read at 120 nm by a spec­ trophotometer within a wavelength of 470 nm. Measurement of superoxide dismutase activity The activity of superoxide dismutase enzyme (SOD) was measured by the Beyer and Fridovich (1987) method. According to this method, the solu­ tion used for the reaction was prepared by mixing 25 mL of 50 mM phosphate buffer (pH 7) with 0.0035 g L­methionine (9.9 mM), 0.004 g NBT (57 μM) and 7.5 μL Triton X­100. One mL of the reaction mixture was blended with 10 μM riboflavin and 20 μL of protein extract. The mixture was placed on a shaker at a dis­ tance of 30 cm from a 20­watt fluorescent lamp for 10 min. Then, the light absorption was measured at 560 nm by a spectrophotometer. Measurement of total soluble carbohydrate To measure total soluble carbohydrates (TSC), 0.5 g of petal tissue was crushed using liquid nitrogen along with 5 mL of 95% ethanol which helped obtain uniform extracts. The supernatant extract was cen­ trifuged for 10 min at 3,500 g. Then, 1 mL of this extract was combined with 3 mL of Anthrone before being transferred to a warm bath of 100°C. The heat caused the appearance of a colored phase after 10 min. Subsequently, the samples were removed from the warm bath and were allowed to cool down at room temperature. Their light absorption was read at 625 nm. The TSC content of petals was determined by creating a standard curve using standard glucose. Rashidiani et al. ‐ Silver nanoparticles effects on ethylene sensitive and no sensitive cut flowe 137 The results were expressed as mg g­1 f.w. (Irigoyen et al., 1992). Measurement of hydrogen peroxide In order to measure the amount of hydrogen per­ oxide (H2O2), the method was similar to the one used by Alexieva et al. (2001). Accordingly, 0.2 g of petal ti s s u e w a s c o m p l e t e l y g r o u n d w i t h 5 m L trichloroacetic acid (TCA). The extract was obtained and centrifuged at 10,000 g for 5 min. Then, 250 μL of the supernatant was mixed with 250 μL of 100 mM phosphate­potassium buffer (pH7) and 500 μL of 1 M of potassium iodide (KI). The absorbance of each sample was read by a spectrophotometer within a wavelength of 390 nm. Statistical analysis This research was conducted as a factorial based on a completely randomized design (CRD), it had three factors that the first factor was the type of flower at 2 levels (carnation and chrysanthemum), second factor was AgNPs at 3 levels (0.04 and 0.08 g L­1 along with deionized water) and the third factor was the sampling time at 4 levels (0, 3, 6 and 9 d of the vase period) with 3 replications, each of which included 8cut flower stems. For measuring the vase life, two factors of the type of flower and the sam­ pling time were not considered and its design was as a CRD with three treatments (AgNPs at 0.04 and 0.08 g L­1 along with deionized water). Data were analyzed using SAS software and a comparison of mean values was made by the LSD test at 5% probability level. 3. Results Relative fresh weight Based on the comparison of mean values, the rel­ ative fresh weight (RFW) of both cut flowers gradual­ ly decreased in the control treatment during the vase period. A faster rate of this decline was observed in carnations, as compared to the chrysanthemum. From the initial days to the ninth day, the decrease of RFW in carnations was about twice as much as the decrease in chrysanthemum. The application of0.04 and 0.08 g L­1 AgNPs caused the percentage of RFW to remain relatively constant in both cut flowers until t h e t h i r d d a y s , b u t t h e n t h e R F W g r a d u a l l y decreased. Furthermore, treating the cut flowers with AgNPs caused a better preservation of their RFW from d 3 to d 9 of the vase period, as compared to the control, but the difference between the two concentrations was no significant. On d 9 of the vase Fig. 3 ­ Effect of two concentrations of AgNPs (0.04 and 0.08 g L­1) along with the control (deionized water) on VSU of two cut flowers during the vase period. Values represent means ± standard error (n=3). LSD at P≤0.05 was used for means comparison. period, the RFW of chrysanthemum was heavier than that of carnations, and the differences were signifi­ cant (Fig. 2). Vase solution uptake There was an increase in the rate of vase solution uptake (VSU) by both flowers until the third day of the vase period, by which time the VSU in carnations was almost twice as much as that in chrysanthemum. From the third day onward, the VSU in both flowers decreased. The application of AgNPs caused an increase in the VSU in both flowers compared to the control. On d 9 of the vase period, the VSU in carna­ tions had been significantly affected by both concen­ trations of AgNPs, whereas the chrysanthemum was only affected by 0.08 g L­1 AgNPs to a substantial degree (Fig. 3). Fig. 2 ­ Effect of two concentrations of AgNPs (0.04 and 0.08 g L­1) along with the control (deionized water) on RFW of two cut flowers during the vase period. Values represent means ± standard error (n=3). Least significant differen­ ce (LSD) at P≤0.05 was used for means comparison. 138 Adv. Hort. Sci., 2020 34(2): 133­145 Bacterial population of stem end The bacterial population of the stem end in carna­ tions increased throughout the vase period. In chrysanthemum, however, the same trend continued until the third days before declining. Both concentra­ tions of AgNPs reduced the bacterial population of the stem end in chrysanthemum during the vase period, making it significantly different when com­ pared to the control on d 9. On the other hand, this trait in carnations was only affected by 0.08 g L­1 AgNPs to make a significant difference compared to the control. In general, in both flowers, 0.08 g L­1 AgNPs was more effective than the 0.04 g L­1 in reducing the bacterial population of the stem end. The highest of this trait among both cut flowers was observed in the control group of chrysanthemum on d 3, whereas the lowest of this value was caused by 0.08 g L­1 AgNPs and measured on d 9 (Fig. 4). Changes in the stem and flower diameter The stem diameter was one of the traits which was not significantly affected by AgNPs in both flow­ ers. Even a comparison between d 0 and 9 of the control groups showed no significant difference. Despite the fact that 0.08 g L­1 AgNPs in both flowers caused the stem diameter to become thicker in com­ parison with the stems of plants treated by 0.04 g L­1 and the control, there were no significant differences between these groups (data not shown). From d 3 onward, the diameter of both flowers decreased. However, it occurred more dramatically in carnations which shrank twice as much as the chrysanthemum. The effect of AgNPs on changing the flower diameter was significant only in carnations, during their vase period. Although AgNPs increased the diameter of flowers in both species, as compared with their respective control groups, the diameters had finally decreased by d 9 of the vase period. On the mentioned day, these treatments had made a significant difference in carnations only, as compared to the carnations control group. In general, the biggest flower diameter was observed in chrysanthe­ mum on d 0 after being treated with 0.04 g L­1 AgNPs, and the smallest of all diameters was obtained in the control group of carnations on d 9 (data not shown). Membrane stability index The decline in values of the membrane stability index (MSI) occurred in both flowers during the vase period, and no significant differences were observed between the two flowers in this respect. In the begin­ ning of the vase period (d 0), the MSI in carnations was higher than in chrysanthemum, but the value of this trait decreased in both flowers through time. On d 9, this decrease was twice as much in carnation when compared to chrysanthemum. In both flowers, AgNPs caused the MSI to increase during the vase period, as compared to the control, but chrysanthe­ mum responded more strongly to the treatment than the extent to which carnations did. In response to AgNPs, chrysanthemum showed a gradual increase in the MSI value ­ so much so that it became slightly ­1 AgNPs can be a successful treatment for increasing the MSI in carnations. In contrast, however, the con­ centration of 0.04 g L­1 worked optimally on chrysan­ themum. In general, the highest value of MSI was observed in carnations on d 0 when treated with 0.08 g L­1 AgNPs, whereas the lowest value occurred in the control on d 9 (Fig. 5). Total soluble protein A comparison of the mean values showed that the Fig. 4 ­ Effect of two concentrations of AgNPs (0.04 and 0.08 g L­1) along with the control (deionized water) on bacterial population of the stem end of two cut flowers during the vase period. Values represent means ± standard error (n=3). LSD at P≤0.05 was used for means comparison. Fig. 5 ­ Effect of two concentrations of AgNPs (0.04 and 0.08 g L­1) along with the control (deionized water) on MSI of two cut flowers during the vase period. Values represent means ± standard error (n=3). LSD at P≤0.05 was used for means comparison. Rashidiani et al. ‐ Silver nanoparticles effects on ethylene sensitive and no sensitive cut flowe 139 content of total soluble protein (TSP) in chrysanthe­ mum petals was about 4 times higher than that of carnation petals on d 0. In carnations, the TSP con­ tent of the petals increased during the vase period. Meanwhile, chrysanthemum underwent a different pattern of change, whereby the content of TSP increased from d 0 to d 3, but then decreased sharply until d 6, and continued to decline at a gradual rate until d 9. The AgNPs increased the TSP in both flow­ ers during the vase period, as compared to the con­ trol. Generally, the highest value of TSP was observed in chrysanthemum on d 3 in the treatment group of 0.04 g L­1 AgNPs, whereas the lowest value was observed in the control on d 9 (Fig. 6). Total soluble carbohydrate The total soluble carbohydrate (TSC) content in carnation petals was more than the content in chrysanthemum petals. In the control groups of both flowers, the content of TSC decreased. The use of AgNPs in both flowers did not cause a significant dif­ ference in TSC on d 0, as compared with the control, but thereafter the difference gradually became signif­ icant until d9. Applying the AgNP at 0.08 g L­1 on car­ nations and at 0.04 g L­1 on chrysanthemum signifi­ cantly increased the TSC in comparison with their respective control groups. In general, carnations responded more strongly to the use of AgNPs, and the increase in their TSC content was much greater than in the case of chrysanthemum. The highest TSC content was measured in carnations on d 3 of the vase period after being treated with 0.08 g L­1 AgNPs. The lowest content was measured in the control group of chrysanthemum on d 9 (Fig. 7). Hydrogen peroxide content The petals of both flowers initially contained simi­ lar amounts of hydrogen peroxide (H2O2) which grad­ ually increased during the vase period. The rate of this increase was higher in carnations compared to the chrysanthemum. When comparing the H2O2 con­ tent between d 0 and d 9, its increase in carnations was about three times more than the increase mea­ sured in chrysanthemum. The application of AgNPs on both flowers reduced the H2O2 content in their p e t a l s , a s c o m p a r e d w i t h t h e c o n t r o l , b u t t h e increase was not prevented completely. On the last day of the vase period, the application of AgNPs on carnations led to a significant difference in H2O2 con­ tent when compared with the control. However, this was not the case in chrysanthemum. In general, the highest amount of H2O2 was measured in the control group of carnations on d 9 of the vase period. Its low­ est amount was obtained in chrysanthemum on d 6 by 0.08 g L­1 AgNPs (Fig. 8). Fig. 6 ­ Effect of two concentrations of AgNPs (0.04 and 0.08 g L­1) along with the control (deionized water) on TSP of two cut flowers during the vase period. Values represent means ± standard error (n=3). LSD at P≤0.05 was used for means comparison. Fig. 7 ­ Effect of two concentrations of AgNPs (0.04 and 0.08 g L­1) along with the control (deionized water) on TSC of two cut flowers during the vase period. Values represent means ± standard error (n=3). LSD at P≤0.05 was used for means comparison. Fig. 8 ­ Effect of two concentrations of AgNPs (0.04 and 0.08 g L­1) along with the control (deionized water) on H2O2 con­ tent of two cut flowers during the vase period. Values represent means ± standard error (n=3). LSD at P≤0.05 was used for means comparison. Adv. Hort. Sci., 2020 34(2): 133­145 140 Peroxidase activity Based on the results, peroxidase (POD) activity in both flowers increased until d 3 of the vase period and then decreased until d 6 before increasing again thereafter. Using AgNPs on chrysanthemum, unlike carnation, significantly increased the activity of POD in comparison with the control. When treated with 0.04 g L­1 AgNPs, the chrysanthemum showed a level of POD activity on d 9 that was about 2.5 times greater than the activity in carnations on the same day. In general, the highest level of POD activity was measured in chrysanthemum on d 9 after the treat­ ment with 0.04 g L­1 AgNPs, whereas the lowest level of activity was measured on d 6 in the control (Fig. 9). Superoxide dismutase activity Based on the results, that the superoxide dismu­ tase (SOD) activity in carnation petals was about 2.5 times higher than that of chrysanthemum petals on d 0, but on d 9 it was completely different, and the activity of this enzyme in chrysanthemum was more than 4.5 times that of carnation. Generally the activi­ ty of SOD dropped in carnation petals, whereas it rose in chrysanthemum petals. The AgNPs decreased the SOD in both flowers during the vase period, as compared to the control. Generally, the highest value of SOD was observed in chrysanthemum on d 9 in the control treatment, whereas the lowest value was observed in carnation on this day of vase period in the treatment group of 0.08 g L­1 AgNPs (Fig. 10). Vase life Clearly, AgNPs caused the vase life of both flowers to increase. Both concentrations had a significant effect on carnations, while chrysanthemum was sig­ nificantly affected by the 0.04 g L­1 only. In carna­ tions, the vase life increased parallel to the increase in applied concentrations of AgNPs from 0.04 to 0.08 g L­1, the effects of which were significantly different compared to each other. Using 0.08 g L­1 AgNPs yield­ ed more appropriate results in carnations. On the other hand, the vase life of chrysanthemum was slightly affected in a negative manner as the concen­ tration of AgNPs rose from 0.04 to 0.08 g L­1, but the difference between the two concentrations was insignificant. Nonetheless, both caused significant differences in comparison with the control (Fig. 11A and B). 4. Discussion and Conclusions In this study, the cut flowers of carnation and chrysanthemum showed various levels of decrease in RFW (Fig. 2), VSU (Fig. 3) and flower diameter throughout the vase period. Similar results have been reported after assessing the RFW and VSU of gerbera cut flowers (Liu et al., 2009), rose (Chamani et al., 2005) and cut gardenia foliage (Lin et al., 2019 a) dur­ ing the vase period. The current study showed that using the AgNPs reduced the bacterial population of the stem end in both flowers, while the RFW was improved as compared to the control. Previous stud­ ies confirm such findings on the use of AgNPs in cut flowers such as Gerbera (Liu et al., 2009; Solgi et al., 2009; Nazari and Koushesh Saba, 2017) and rose (Lu et al., 2010; Nazemi Rafi and Ramezanian, 2013; Hassan et al., 2014). These studies showed that the vase life improves when the bacterial population of the stem end decreases, besides when the VSU and RFW increase. Fig. 9 ­ Effect of two concentrations of AgNPs (0.04 and 0.08 g L­1) along with the control (deionized water) on POD acti­ vity of two cut flowers during the vase period. Values represent means ± standard error (n=3). LSD at P≤0.05 was used for means comparison. Fig. 10 ­ Effect of two concentrations of AgNPs (0.04 and 0.08 g L­1) along with the control (deionized water) on SOD activity of two cut flowers during the vase period. Values represent means ± standard error (n=3). LSD at P≤0.05 was used for means comparison. Rashidiani et al. ‐ Silver nanoparticles effects on ethylene sensitive and no sensitive cut flowe 141 The decrease in the RFW of cut flowers marks the beginning of senescence in flowers, and the more the flowers become closer to the process of senescence, their ability to take up water from the vase is reduced. The imbalance between water uptake and transpiration distorts cell turgor, thereby causing the flowers to wither (Reid and Jiang, 2012). The survival of cut flowers depends largely on a positive water balance: an increase in water uptake and a decrease in water loss (Halevy and Mayak, 1981; Van Doorn, 1997). After being placed in the vase, the flower loses RFW in part because of vascular occlusion and the growth of microorganisms which grow in the vase solution. They reduce the water uptake by blocking the stem end and vessels, thereby causing water stress which is a main factor in the reduction of vase life (van Doorn, 1997; Macnish et al., 2005). Adding a germicide to the vase solution may control the activi­ ty of microbes. It has been reported that adding antimicrobial compounds containing Ag+ ions to the vase solution improves the vase life of cut flowers (Hassan et al., 2014). AgNPs nanoparticles function effectively because of their high surface­to­volume ratio and their crystallographic surface structure (Rai et al., 2009). Furthermore, Ag+ ions cause bacterial cell death by affecting membrane structure and per­ meability, inhibiting DNA transcription, disrupting transport activity and changing cellular content and ATP (Feng et al., 2000; Sondi and Salopek­Sondi, 2004; Rai et al., 2009; Dakal et al., 2016). This difference in the bacterial population of the stem end of the two cut flowers may depend on the genotype of the plant, as well as the extract and metabolites that are secreted from the stem end and are released into the vase solution, thereby affecting the growth of bacteria. Phenolic compounds are sec­ ondary metabolites that are involved in plant defense against pathogens (Naczk and Shahidi, 2004). In tradi­ tional Chinese medicine, the flowering heads of Chrysanthemum indicum are used as a source of bac­ tericide, with additional antifungal and antiviral prop­ erties (Shunying et al., 2005). In agreement with our results, Shunying et al. (2005) showed that the chemi­ cal composition and secondary metabolites of Ch. indicum possess antimicrobial activity. Flower diameters in this study were significantly influenced by AgNPs in carnation flowers, butthe effect on chrysanthemum was not significant. Dar et al. (2014) reported that the flower diameter in Dianthus chinensis first increased and then finally decreased during post­harvest development and senescence, respectively. The current research showed that the flower diameter of carnations tends to increase after being treated with AgNPs. This accords closely witha previous report on Polianthes tuberosa which was treated with 0.015 g L­1 AgNPs and led to a significant increase in the diameter of flowers (Bahrehmand et al., 2014). It is well known that the MSI gradually decreases from the time when the flowers open to the time of their senescence. Such a trend occurs evidently in certain flowers such as Lilium (Bieleski and Reid, 1992), rose (Hassan et al., 2014) and Iris (Ahmad and Tahir, 2016). The senescence process is mainly asso­ ciated with protein loss, increased lipid peroxidation, membrane leakage, cell wall component degradation a n d c e l l u l a r m e m b r a n e d i s r u p ti o n ( B u c h a n a n ­ Wollaston, 1997). AgNPs may preserve the mem­ brane stability by curbing the peroxidation of lipids (Hatami and Ghorbanpour, 2013). There was a lower percentage of MSI in carnation petals, compared to chrysanthemum, which may be due to the fact that carnations are highly sensitive to ethylene. The rea­ son becomes clear when knowing that ethylene Fig. 11 ­ Effect of two concentrations of AgNPs (0.04 and 0.08 g L­1) along with the control (deionized water) on vase life of carnation (A) and chrysanthemum (B). Values repre­ sent means ± standard error (n=3). LSD at P≤0.05 was used for means comparison. Adv. Hort. Sci., 2020 34(2): 133­145 142 degrades the cell membrane and increases its leak­ age (van Doorn and Woltering, 2008), thereby result­ ing in a lower value of MSI. However, AgNPs acts against the production of ethylene (Hassan et al., 2014). In fact, AgNPs induce an efficient cellular elec­ tron exchange mechanism which reduces electron leakage and, subsequently, limits the creation of ROSs. AgNPs also dys regulate lipid peroxidation and have a propensity to maintain the MSI (Lu et al., 2010; Hassan et al., 2014). Previous studies have reported a decrease in TSP content and an increase in protease activity during the vase life of cut flowers (Wagstaff et al., 2005; Dar et al., 2014; Zhao et al., 2018). Quite differently, however, we concluded that changes in the TSP con­ tent may vary depending on the type of flower, species and cultivar. Still, contrary to our results, Dar et al. (2014) showed that protein degradation in Dianthus chinensis is a key factor in regulating the senescence process of flowers. Shahri et al. (2011) also reported that TSP decreased during the senes­ c e n c e p r o c e s s o f H e l l e b o r u s o r i e n t a l i s c v . ‘Olympicus’, while there was an increase in its low­ molecular­weight proteins. Accordingly, realizing an increase of TSP content in carnation petals could be a result of these low­molecular­weight proteins. I t h a s b e e n s h o w n t h a t i n fl o w e r s s u c h a s Helleborus orientalis and Dianthus chinensis, the TSC is reduced during the senescence process (Shahri et al., 2011; Dar et al., 2014).There was a lower content of TSC in chrysanthemum petals, as compared with carnations, which may be due to the genetic differ­ ences between the two plants, as well as the differ­ ence in the rate of polysaccharide decomposition during the opening and development of flowers and petals. In agreement with our results, it has been found that the starch and fructan polysaccharides are degraded and reduced during the development of flowers and the expansion of petals in chrysanthe­ mum (Trustyl and Miller, 1991). Therefore, in this study, AgNPs in both flowers may have benefited the vase life by maintaining the content of TSC in petals and by promoting the mechanisms through which carbohydrates stabilize the cell membrane (Ashraf et al., 2010). Furthermore, AgNPs regulate and protect the cellular osmotic potential, inhibit the formation of free radicals (Parida and Das, 2005) and regulate the expression of genes (Rahdari et al., 2012). Usually, the amount of H2O2 increases in plant cells during senescence (Ezhilmathi et al., 2007; Saeed et al., 2014). It can be suggested that high lev­ els of H2O2 in carnation petals occur because of the plants sensitivity to ethylene. This can be compared with chrysanthemum which is not sensitive to the hormone. Our results showed that the use of AgNPs on both flowers reduced the production of H2O2 in petals, as compared with the control. These results accord closely with a previous report by Hassan et al. (2014) where the production of H2O2 became signifi­ cantly limited in roses because AgNPs was used. Senescence is an oxidation process in which ROS and antioxidant systems are involved (Buchanan­ Wollaston, 1997). Plant cells have developed a series of antioxidant mechanisms for defense to prevent the production of ROSs and to limit their destructive effects on proteins, fats and nucleic acids (Arora et al., 2002). The enzymatic part of this system consists of antioxidant enzymes such as SOD, POD, catalase (CAT) and ascorbate peroxidase (APX) which degrade all types of ROSs (Balakhnina and Borkowska, 2013). Depending on the species or type of cultivars, the POD activity and SOD enzymes can exhibit different patterns of change in cut flowers during the senes­ cence process (Hassan et al., 2014). As the produc­ tion of H2O2 increased in the petals of both flowers during the vase period, the POD enzyme likewise increased its activity to scavenge the higher amounts of H2O2. Furthermore, Hassan et al. (2014) reported similar results which indicate that petals of the rose cut flower cv. ‘First Red’ ­ which is sensitive to ethyl­ ene (Chamani et al., 2005) ­ showed declining levels of SOD activity during the vase period. However, con­ trary to our results on the incremental trend of POD in carnations and chrysanthemum during the vase period, Hassan et al. (2014) reported that the POD activity in the rose cultivar decreases. It has also been reported that SOD activity in ethylene­sensitive flowers such as carnation is relatively lower com­ p a r e d t o e t h y l e n e ­ i n s e n s i ti v e fl o w e r s s u c h a s chrysanthemum. This comprises a major factor in accelerating the senescence (Bartoli et al., 1995). In addition, it may be suggested that in ethylene­ insensitive flowers such as chrysanthemum, ROS cause the greatest amount of damage to the cell components, thereby leading to a shorter vase life. For this reason, the SOD activity has to increase so as to create a parallel level of scavenging. In certain flowers such as carnations, which are sensitive to ethylene, the level of SOD activity may not be pro­ nounced as much. As previously mentioned, AgNPs cause the plants to acquire an efficient cellular elec­ tron exchange mechanism, whereby the electron leakage and ROS production are reduced (Hassan et al., 2014). Perhaps, the activity of SOD does not Rashidiani et al. ‐ Silver nanoparticles effects on ethylene sensitive and no sensitive cut flowe 143 increase in carnations even when AgNPs are applied. AgNPs increased the vase life of chrysanthemum and carnation (Figs. 11A and B) by increasing the RFW (Fig. 2) and reducing the bacterial population of the stem end (Fig. 4). The scientific literature con­ tains several reports that mention the efficiency of AgNPs in increasing the vase life of gerbera (Liu et al., 2009; Solgi et al., 2009; Nazari and Koushesh Saba, 2 0 1 7 ) , r o s e ( L u e t a l . , 2 0 1 0 ; N a z e m i R a fi a n d Ramezanian, 2013; Hassan et al., 2014), chrysanthe­ mum (Carrillo­López et al., 2016), carnation (Naing et al., 2017) and gladiolus (Li et al., 2017). In conclusion, AgNPs improved the vase life of both cut flowers by contributing to the values of their RFW, VSU, flower diameter, MSI, TSC, TSP and POD activity and by limiting their bacterial population of the stem end and H2O2 levels, as compared to the control. It is highly probable that AgNPs are capable of reducing the expression of genes responsible for the production of ethylene, as well as limiting the rate of transpiration and the opening of stoma. Furthermore, AgNPs have roles in regulating the aperture of the stoma and in reducing MDA produc­ tion, thereby prolonging the vase life of cut flowers. Ultimately, this research revealed that the use of AgNPs at 0.04 g L­1and 0.08 g L­1 can extend the vase life of at least two cultivars belonging to chrysanthe­ mum and carnation, respectively. Acknowledgements The authors wish to thank the University of Kurdistan for providing facilities and financial support (Grant No. CRC97­00242­1) of this research. References ABELES F., MORGAN P., SALTVEIT J.R.M., 1992 ­ Ethylene in plant biology. ­ Academic Press, San Diego, CA, USA, pp. 399. AHMAD S.S., TAHIR I., 2016 ­ Increased oxidative stress, lipid peroxidation and protein degradation trigger senescence in Iris versicolor L. flowers. ­ Physiol. Mol. Biol. Plants, 22 (4): 507­514. ALEXIEVA V., SERGIEV I., MAPELLI S., KARANOV E., 2001 ­ The effect of drought and ultraviolet radiation on growth and stress markers in pea and wheat.­ Plant Cell Environ., 24: 1337­1344. ARORA A., SAIRAM R., SRIVASTAVA G., 2002 ­ Oxidative stress and antioxidative system in plants. ­ Curr. Sci., 82: 1227­1238. ASHRAF M., AHMAD R., BHATTI A., AFZAL M., SARWAR A., MAQSOOD M., KANWAL S., 2010 ­ Amelioration of salt stress in sugarcane (Saccharum officinarum L.) by sup‐ p l y i n g p o t a s s i u m a n d s i l i c o n i n h y d r o p o n i c s . ­ Pedosphere, 20: 153­162. BAHREHMAND S., RAZMJOO J., FARAHMAND H., 2014 ­ Effects of nano‐silver and sucrose applications on cut flower longevity and quality of tuberose (Polianthes tuberosa).­ Int. J. Hortic. Sci. Technol., 1: 61­77. BALAKHNINA T., BORKOWSKA A., 2013 ­ Effects of silicon on plant resistance to environmental stresses.­ Int. Agrophys., 27: 225­232. BALESTRA G.M., AGOSTINI R., BELLINCONTRO A., MEN­ CARELLI F., VARVARO L., 2005 ­ Bacterial populations related to gerbera (Gerbera jamesonii L.) stem break.­ Phytopathol. Mediterr., 44: 291­299. BARTOLI C.G., SIMONTACCHI M., GUIAMET J.J., MONTALDI E., 1995 ­ Antioxidant enzymes and lipid peroxidation during aging of Chrysanthemum morifolium RAM petals. ­ Plant Sci., 104: 161­168. BEYER W.F., FRIDOVICH I., 1987 ­ Assaying for superoxide dismutase activity: some large consequences of minor changes in conditions. ­ Anal. Biochem., 161: 559­566. BIELESKI R.L, REID M.S., 1992 ­ Physiological changes accompanying senescence in the ephemeral daylily flower.­ Plant Physiol., 98: 1042­1049. BRADFORD M.M., 1976 ­ A rapid and sensitive method for the quantitation of microgram quantities of protein uti‐ lizing the principle of protein‐dye binding. ­ Anal. Biochem., 72: 248­254. BUCHANAN­WOLLASTON V., 1997 ­ The molecular biology of leaf senescence. ­ J. Exp. Bot., 48: 181­199. CARRILLO­LÓPEZ L.M., MORGADO­GONZÁLEZ M., MORGA­ DO­GONZÁLEZ A., 2016 ­ Biosynthesized silver nanopar‐ ticles used in preservative solutions for Chrysanthemum cv. Puma. ­ J. Nanomater., 1­10. CHAMANI A.B.E., KHALIGHI B.A., JOYCE A.D.C., DONALD E., IRVING A., ZAMANI B.Z.A., MOSTOFI B.Y., KAFI B.M., 2005 ­ Ethylene and anti‐ethylene treatment effects on cut ‘First Red’ rose. ­ Appl. Hortic., 7(1): 3­7. CHANDLER S.F., SANCHEZ C., 2012 ­ Genetic modification; the development of transgenic ornamental plant vari‐ eties.­ Plant Biotechnol. J., 10: 891­903. CHAU C.F., WU S.H., YEN G.C., 2007 ­ The development of regulations for food nanotechnology. ­ Trends Food Sci. Technol., 18: 269­280. DAKAL T.C., KUMAR A., MAJUMDAR R.S., YADAV V., 2016 ­ Mechanistic basis of antimicrobial actions of silver nanoparticles. ­ Front Microbiol., 7: 1831. DAMUNUPOLA J.W., JOYCE D.C., 2008 ­ When is a vase solution biocide not, or not only, antimicrobial? ­ J. Jpn. Soc. Hortic. Sci., 77: 211­228. DAR R.A., TAHIR I., AHMAD S.S., 2014 ­ Physiological and biochemical changes associated with flower develop‐ ment and senescence in Dianthus chinensis L ­ Ind. J. Plant Physiol., 19: 215­221. DEVECCHI M., TROTTA F., SEGLIE L., KIM Y.J., LAVA C., Adv. Hort. Sci., 2020 34(2): 133­145 144 DOLCI M., SCARIOT V., 2009 ­ Effects of anti‐ethylene compounds included in nanosponges in improving the postharvest longevity of carnation (Dianthus caryophyl­ lus) and buttercup (Ranunculus asiaticus) cut flowers. ­ Acta Horticulturae, 847: 237­244. DOLE J.M., WILKINS H.F., 2005 ­ Floriculture: Principles and species. ­ Prentice­Hall Inc, Upper Saddle River, New Jersey, USA, pp. 1023. EZHILMATHI K., SINGH V.P., ARORA A., SAIRAM R.K., 2007 ­ Effect of 5‐sulfosalicylic acid on antioxidant activity in relation to vase life of Gladiolus cut flowers. ­ Plant Growth Regul., 51: 99­108. FENG Q.L., WU J., CHEN G., CUI F., KIM T., KIM J., 2000 ­ A mechanistic study of the antibacterial effect of silver ions on Escherichia coli and Staphylococcus aureus. ­ J. Biomed. Mater. Res., 52: 662­668. HALEVY A.H., MAYAK S., 1981 ­ Senescence and posthar‐ vest physiology of cut flowers. Part 2. ­ Hortic. Rev., 3: 59­143. HASSAN F.A.S., ALI E.F., EL­DEEB B., 2014 ­ Improvement of postharvest quality of cut rose cv. ‘First Red’ by biologi‐ cally synthesized silver nanoparticles. ­ Sci. Hortic., 179: 340­348. HATAMI M., GHORBANPOUR M., 2013 ­ Effect of nanosil‐ ver on physiological performance of pelargonium plants exposed to dark storage. ­ J. Hortic. Res., 21: 15­ 20. HE S., JOYCE D.C., IRVING D.E, FARAGHER J.D., 2006 ­ Stem end blockage in cut Grevillea ‘Crimson Yul‐lo’ inflores‐ cences. ­ Postharv. Biol. Technol., 41: 78­84. HEMEDA H.M., KLEIN B., 1990 ­ Effects of naturally occur‐ ring antioxidants on peroxidase activity of vegetable extracts. ­ J. Food Sci., 55: 184­185. IRIGOYEN J., EINERICH D., SÁNCHEZ­DÍAZ M., 1992 ­ Water stress induced changes in concentrations of proline and total soluble sugars in nodulated alfalfa (Medicago sati­ va) plants. ­ Physiol. Plant., 84: 55­60. JONES M.L., 2013 ­ Mineral nutrient remobilization during corolla senescence in ethylene‐sensitive and ‐insensitive flowers.­ AoB Plants, 5: plt023. KIM J.H., LEE A.K., SUH J.K., 2005 ­ Effect of certain pre‐ treatment substances on vaselife and physiological characters in Lilium spp. ­ Acta Horticulturae, 673: 307­ 314. LI H., LI H., LIU J., LUO Z., JOYCE D., HE S., 2017 ­ Nano‐sil‐ ver treatments reduced bacterial colonization and biofilm formation at the stem‐ends of cut gladiolus ‘Eerde’ spikes. ­ Postharv. Biol. Technol., 123: 102­111. LIN X., LI H., LIN S., XU M., LIU J., LI Y., HE S., 2019 b ­ Improving the postharvest performance of cut spray ‘Prince’ carnations by vase treatments with nano‐silver and sucrose. ­ J. Hortic. Sci. Biotechnol., 94: 513­521. LIN S., LI H., XIAN X., LIN X., PANG Z., LIU J., HE S., 2019 a ­ N a n o ‐ s i l v e r p r e t r e a t m e n t d e l a y s w i l ti n g o f c u t Gardenia foliage by inhibiting bacterial xylem blockage. ­ Sci. Hortic., 246: 791­796. LIU J., HE S., ZHANG Z., CAO J., LVP., HE S., CHENG G., JOYCE D.C., 2009 ­ Nano‐silver pulse treatments inhibit stem‐end bacteria on cut gerbera cv. Ruikou flowers. ­ Postharv. Biol. Technol., 54: 59­62. LU P., CAO J., HE S., LIU J., LI H., CHENG G., DING Y., JOYCE D.C., 2010 ­ Nano‐silver pulse treatments improve water relations of cut rose. ­ Postharv. Biol. Technol., 57: 196­202. MACNISH A., LEONARD R., HUGHE K., NELL T., 2005 ­ Bacteria‐free solutions. ­ Florists’ Rev., 57­60. MAITY T.R., SAMANTA A., SAHA B., DATTA S., 2019 ­ Evaluation of Piper betle mediated silver nanoparticle in post‐harvest physiology in relation to vase life of cut spike of Gladiolus. ­ Bull. Nat. Res. Cent., 43: 1­11. NACZK M., SHAHIDI F., 2004 ­ Extraction and analysis of phenolics in food. ­ J. Chromatogr., 1054: 95­111. NAING A.H., WIN N.M., HANG J.S., LIM K.B., KIM C.K., 2017 ­ R o l e o f n a n o s i l v e r a n d t h e b a c t e r i a l s t r a i n Enterobacter cloacae in increasing vase life of cut car‐ nation ‘Omea’. ­ Front. Plant Sci.,8: 1590. NAZARI F., KOUSHESH SABA M., 2017 ­ Combination effect of 1‐methylcyclopropene (1‐MCP) with ajowan essen‐ tial oil and silver nanoparticles on postharvest life of gerbera (Gerbera jamesonii) cut flowers. ­ HortSci., 52: 1550­1555. NAZEMI RAFI Z., RAMEZANIAN A., 2013 ­ Vase life of cut rose cultivars ‘Avalanche’ and ‘Fiesta’ as affected by Nano‐silver and S‐carvone treatments. ­ S. Afr. J. Bot., 86: 68­72. PARIDA A.K., DAS A.B., 2005 ­ Salt tolerance and salinity effects on plants, a review. ­ Ecotox. Environ. Safe., 60: 324­349. PROCHAZKOVA D., WILHELMOVA N., 2007 ­ Leaf senes‐ cence and activities of the antioxidant enzymes. ­ Biol. Plant., 51: 401­406. RAHDARI P., TAVAKOLI S., HOSSEINI S.M., 2012 ­ Studying of salinity stress effect on germination, proline, sugar, protein, lipid and chlorophyll content in purslane (Portulaca oleracea L.) leaves. ­J. Stress Physiol. Biochem., 8: 182­193. RAI M., YADAV A., GADE A., 2009 ­ Silver nanoparticles as a new generation of antimicrobials. ­ Biotechnol. Adv., 27: 76­83. REID M.S., JIANG C.Z., 2012 ­ Postharvest biology and tech‐ nology of cut flowers and potted plants. ­ Hortic. Rev., 40: 1­54. SAEED T., HASSAN I., ABBASI N.A., JILANI G., 2014 ­ Effect of gibberellic acid on the vase life and oxidative activi‐ ties in senescing cut gladiolus flowers. ­ Plant Growth Regul., 72: 89­95. SAIRAM R.K., RAO K.V., SRIVASTAVA G., 2002 ­ Differential response of wheat genotypes to long term salinity stress in relation to oxidative stress, antioxidant activity and osmolyte concentration. ­ Plant Sci., 163: 1037­ 1046. SCARIOT V., PARADISO R., ROGERS H., DE PASCALE S., 2014 ­ Ethylene control in cut flowers. Classical and innovative approaches. ­ Postharv. Biol. Technol., 97: Rashidiani et al. ‐ Silver nanoparticles effects on ethylene sensitive and no sensitive cut flowe 145 83­92. SEGLIE L., MARTINA K., DEVECCHI M., ROGGERO C., TROT­ TA F., SCARIOT V., 2011 ­ The effects of 1‐MCP in cyclodextrin‐based nanosponges to improve the vase life of Dianthus caryophyllus cut flowers. ­ Postharv. Biol. Technol., 59: 200­205. SHAHRI W., TAHIR I., ISLAM S.T., BHAT M.A., 2011 ­ Physiological and bio‐chemical changes associated with flower development and senescence in so far unex‐ plored Helleborus orientalis Lam.cv. Olympicus. ‐ Physiol. Mol. Biol. Plants, 17: 33­39. SHUNYING Z., YANG Y., YU H., YING Y., ZOU G., 2005 ­ Chemical composition and antimicrobial activity of the e s s e n ti a l o i l s o f C h r y s a n t h e m u m i n d i c u m . ­ J . Ethnopharmacol., 96: 151­158. SOLGI M., KAFI M., TAGHAVI T.S., NADERI R., 2009 ­ Essential oils and silver nanoparticles (SNP) as novel a g e n t s t o e x t e n d v a s e ‐ l i f e o f g e r b e r a ( G e r b e r a jamesonii cv. Dune) flowers. ­ Postharv. Biol. Technol., 53: 155­158. SONDI I., SALOPEK­SONDI B., 2004 ­ Silver nanoparticles as antimicrobial agent, a case study on E. coli as a model for Gram‐negative bacteria. ­ J. Colloid Interface Sci., 275: 177­182. TAVALLALI H., POURESMAEIL S., 2012 ­ Determination of ascorbic acid by modified method based on photolumi‐ nescence of silver nanoparticles. ­ Int. J. Chem. Tech. Rese., 4: 304­310. TRUSTYL S.E., MILLER W.B., 1991 ­ Postproduction carbo‐ hydrate levels in pot Chrysanthemums. ­ J. Amer. Soc. Hortic. Sci., 116: 1013­1018. VAN DOORN W.G., 1997 ­ Effects of pollination on floral attraction and longevity. ­ J. Exp. Bot., 48: 1615­1622. VAN DOORN W.G., VASLIER N., 2002 ­ Wound‐induced xylem occlusion in stems of cut chrysanthemum flow‐ e r s : r o l e s o f p e r o x i d a s e a n d c a t e c h o l o x i d a s e . ­ Postharv Biol. Technol., 26: 275­284. VAN DOORN W.G., WOLTERING E.J., 2008 ­ Physiology and molecular biology of petal senescence. ­ J. Exp. Bot., 59: 453­480. WAGSTAFF C., CHANASUT U., HARREN F.J., LAARHOVEN L.J., THOMAS B., ROGERS H.J, STEAD A.D., 2005 ­ Ethylene and flower longevity in Alstroemeria: relation‐ ship between tepal senescence, abscission and ethylene biosynthesis. ­ J. Exp. Bot., 56: 1007­1016. YANG S.F., HOFFMAN N.E., 1984 ­ Ethylene biosynthesis and its regulation in higher plants. ­ Annu. Rev. Plant Biol., 35: 155­189. ZHAO D., CHENG M., TANG W., LIU D., ZHOU S., MENG J., TAO J., 2018 ­ Nano‐silver modifies the vase life of cut herbaceous peony (Paeonia lactiflora Pall.) flowers. ­ Protoplasma, 1: 1­13.