Impaginato 187 Adv. Hort. Sci., 2019 33(2): 187-195 DOI: 10.13128/ahs-24261 The roles of sodium nitroprusside, salicylic acid, and methyl jasmonate as hold solutions on vase life of Gerbera jamesonii ‘Sun Spot’ E. Hemati, M.R. Salehi Salmi (*), M.H. Daneshvar, M. Heidari Department of Horticultural Science, Agricultural Sciences and Natural Resources University of Khuzestan, Khuzestan, Iran. Keywords: antioxidant enzyme, ethylene, plant growth regulator, post-harvest, sugar. Abstract: The present study investigates the roles of nitroprusside (SNP), sali- cylic acid (SA), methyl jasmonate (MJ), and their interaction with 8-hydrox- yquinoline sulfate (8-HQS) in regulating the peroxidase activity (POX), water uptake, the relative water content (RWC), the contents of malondialdehyde (MDA), soluble sugar, proline, and protein content in the petals and the stem bending of Gerbera jamesonii ‘Sun Spot’ cut flowers. Cut flowers were treated with various concentrations (50, 100, and 200 µM) of hold-solutions containing 8-HQS, SA, MJ, and SNP. Hold solutions were used alone or in combination with 100 µM 8-HQS for 24 h. Distilled water was used as control and sucrose (4%, w/v) was added to all solutions. The findings showed that 50 µM SA+ 100 µM 8- HQS markedly improved the RWC, the contents of proline, anthocyanin, carotenoid, protein, and soluble sugar, and activities of POX in the petals and markedly reduced water loss and the contents of MDA in the petals, compared with other treatments, especially the control. Meanwhile, the combination of plant growth regulators (PGR) with 8-HQS markedly improved positive indexes than use alone PGR. This phenomenon seemed to be due to more absorption of PGR. Among different concentrations of PGR, 50 μM is the most effective treat- ment for the improvement of the vase life of Gerbera jamesonii cut flowers. The results also demonstrated that SA+8-HQS improves the vase life of gerbera cut flowers by enhancing the membrane stability and water retaining capacity as well as increasing proline, antioxidant activity, and pigment contents. 1. Introduction Vase life and quality are key factors that contribute to the aesthetic and benefits of cut flowers (Mansouri, 2012). The short vase life of most cut flowers is mainly due to the water loss, which is an important physio- logical process that affects the main quality characteristics of cut flowers, such as appearance (Salehi Salmi et al., 2018). Gerbera jamesonii is a commercially popular cut flower that ranks 10 in the globe auctions. This plant is a member of the family asteraceae that (*) Corresponding author: mrsalehisalmi@gmail.com Citation: HEMATI E., SALEHI SALMI M.R., DANESHVAR M.H., HEIDARI M., 2019 - The roles of sodium nitroprusside, salicylic acid, and methyl jasmona- te as hold solutions on vase life of Gerbera jame- sonii ‘Sun Spot’. - Adv. Hort. Sci., 33(2): 187-195 Copyright: © 2019 Hemati E., Salehi Salmi M.R., Daneshvar M.H., Heidari M. 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 29 November 2018 Accepted for publication 15 February 2019 AHS Advances in Horticultural Science http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ Adv. Hort. Sci., 2019 33(2): 187-195 188 originates from Africa and Madagascar and extends to China (Parthasarathy and Nagaraju, 1999; Hind, 2007). Sensitivity to microbial contamination at the stem base is a major postharvest problem of this plant (Balestra et al., 2005). Microorganisms cause stem end blockage in cut flower (He et al., 2006; Liu et al., 2009) and also secretion of toxic compounds, and thereby accelerated wilting (Williamson et al., 2002). Vase life of gerbera has been studied exten- sively with different treatments (Nair et al., 2003; Solgi et al., 2009; Shabanian et al., 2018). Witte et al. (2014) reported that treating cultivars of gerbera stems by sucrose in combination with an antimicro- bial compound (HQC, Chlorine) resulted in less bend- ing than the same concentration of the antimicrobial compounds alone. Perik et al. (2014) noted that other factors might also be involved in bending and showed that a mixture of chemicals delayed the time to bending in six tested cultivars of gerbera. Sodium nitroprusside (SNP), the inorganic nitrous compound (nitroferricyanide) with the formula Na2[Fe(CN)5NO].2H2O, is an important signaling mol- ecule. This molecule has diverse physiological func- tions for plants such as inducing tolerance to adverse environmental factors (Shi et al., 2016; Kumar Rai et al., 2018). Application of SNP in vase solution result- ed in extending the vase life of gerbera cut flowers (Shabanian et al., 2018); however, there is very limit- ed information regarding the positive effects of exogenously applied SNP in extending the vase life. Ortho-hydroxybenzoic acid or salicylic acid is an endogenous plant growth regulator. Exogenous application of salicylic acid (SA) can affect the antioxi- dant capacity of plant cells and prolong vase life of cut flowers, such as rose (Alaey et al., 2011) and anthurium (Promyou et al., 2012). However, little work has been reported on the role of SA on cut flower vase-life improvement and physio-chemical attributes related to senescence. Methyl Jasmonate (MJ) has been found as a natu- rally occurring substance in higher plants. In this con- text, the application of MJ induced antioxidant sys- tem activity can suppress fungal infection and enhance stress resistance (Kanani and Nazarideljou, 2017). To our knowledge, MJ effects on specific phys- iological and biochemical processes in gerbera cut flower have not been studied yet. As a derivative of 8-hydroxyquinolines, 8-hydrox- yquinoline sulfate is widely used as antibacterial since the beginning of the 1950s. This compound is a c t i v e a g a i n s t g r a m - n e g a t i v e b a c t e r i a o f t h e Enterobacteriaceae family, fungi of the Candida genus, and mycoplasma (Chupakhina et al., 2012). In previous studies, 8-hydroxyquinoline sulfate (8-HQS) remarkably increased vase life of rose cut flowers (Ichimura et al., 1999). In the present study, the role of three plant growth regulators (i.e., SNP, MJ, and SA) in regulating the activities of the antioxidant enzyme, relative water content (RWC), water uptake, the contents of malondialdehyde (MDA), protein, pigments and solu- ble sugar in the petals, and time of stem bending of gerbera cut flowers were investigated. The objective of the present study is to provide a theoretical basis for the application and optimization dosage of plant growth regulators in combination with an antimicro- bial compound, i.e., 8-HQS, in improving the vase life of gerbera cut flowers during the vase-holding period. 2. Materials and Methods Plant material and treatment ‘Sun Spot’ cut-gerberas (Gerbera jamesonii), har- vested at normal harvest maturity, were obtained from a commercial grower (Dezfol, Khuzestan, Iran). The length of the stem varied between 65 and 70 cm. The harvested flowers were packed into parchment paper and transported to the laboratory within 1-2 h. Then, stems were re-cut to a uniform length of 55, under distilled water to avoid air embolism. Each six- flower sample was placed randomly in 250 mL of var- ious concentrations (50, 100, and 200 µM) of hold- solutions containing 8-HQS, SA, MJ, and SNP. Hold solutions were used alone or in combination with 100 µM 8-HQS for 24 h. Distilled water was used as control and sucrose (4%, w/v) was added to all solu- tions. To maintain the proper concentrations of hold- solutions, the mouths of the vases were covered with plastic wrap (around the stem) to minimize evapora- tion and to prevent contamination. Then, flowers were individually sited in glass bottles of 25 cm height, approximately 150 ml of distilled water in each bottle, under laboratory condition. The labora- tory was maintained at 22°C, 60±5% relative humidi- ty, and 16 mmol m-2 s-1 photons irradiance using cool fluorescent lamps for a 12 h photoperiod (07:00- 19:00 h). Measurements - Time of stem bending was determined as described by Perik et al. (2012). - Relative fresh weight (RFW) was calculated by the Hemati et al. - Plant growth regulators as hold solutions of cut-flower Gerbera 189 following formula: RFW (%) = [(FW t=10 -FW t=0 )/ FW t=0 ] ×100 where FWt=10 is the fresh weight of flower (g) at 10th day and FWt=0 is the fresh weight of the same flower (g) at first day (He et al., 2006). - Water uptake (mL) was calculated by subtracting in the weight of the remaining water at the end of the experiment from the initial weight. - Soluble carbohydrate content in petals was mea- sured by the anthrone colorimetric method accord- ing to the method of Xue (1985). - Total anthocyanin content of petal was measured by the pH differential method of Yang et al. (2009). - Total carotenoid content of gerbera petal tissue was estimated using the method of Wellburn (1994). - Flavonoid petal tissue was measured according to the method of Markham (1982). - Protein content in petal was estimated by the method of Bradford (1976) using bovine serum albu- min as the protein standard. - Malondialdehyde (MDA) content in petals was measured by the thiobarbituric acid reaction follow- ing the procedure of Hodges et al. (1999). - Peroxidase (POX) activity was evaluated by oxida- tion of guaiacol, as a substrate, according to Chance and Maehly (1955). Statistical analysis Data were analyzed using analysis of variance (ANOVA) in SAS software. Means were compared by one-way ANOVA and Duncan’s multiple range test at the 5% level of significance. 3. Results and Discussion Vase life As shown in figure 1, hold-solutions affected senescence of Gerbera jamesonii in a dose-depen- dent manner. Compared with control, different con- centrations of SA, with or without 8-HQS, all pro- longed the senescence of gerbera as shown by the tighter stem and more showy flowers. Compared with other concentrations of SA, 50 µM SA+ 100 µM 8-HQS markedly prolonged the longevity of the cut flowers. As shown in figure 1, different concentra- tions of SNP, with or without 8-HQS, all prolonged the length of vase life of gerbera cut flower, com- pared with control. Compared with control, 50 µM, 100 µM, and 200 µM SNP noticeably increased the length of vase life of Gerbera jamesonii cut flower by 65%, 78%, and 43%, respectively. However, there was no significant difference in the stem bending of flowers among different concentrations of SNP. Among various concentrations of 8-HQS, stem bend- ing of cut flowers treated by 100 μM 8-HQS was sig- nificantly lower than those treated by other concen- trations. Compared with control, 50, 100, and 200 μM 8-HQS increased the vase life by 69%, 100%, and 78%, respectively. Different concentrations of MJ all significantly increased vase life, compared with the control (Fig. 1). However, MJ treatments were less effective on vase life compared with 8-HQS, SA, and SNP treatments. Shabanian et al. (2018) showed that SNP extend- ed the vase life of gerbera cut flowers as compared with their respective control treated with water alone. In agreement with this finding, treatments with SNP extended the vase life of other cut flowers, e.g., carnation (Zeng et al., 2011), chrysanthemums (Mansouri, 2012), gladiolus (Dwivedi et al., 2016), and rose (Liao et al., 2013). The mechanism of SA action, as a hold solution, in vase life of cut flowers has not been clarified; however, published data sug- gest some association with ethylene production. Zhang et al. (2003) showed that application of SA resulted in suppression ACC synthase and ACC oxi- dase activities and biosynthesis of ethylene in kiwifruit. In Gladiolus, the maximum vase-life was obtained once flowers treated with a solution con- taining 100-ppm 5-sulfosalicylic acid + 4% sucrose (Ezhilmathi et al., 2007). 8-HQS is a subclass of quinolones with a wide variety of biological effects. The 8-hydroxyquinoline derivatives emerged as a hold-solutions being widely explored for several bio- logical functions such as antifungal effects (Oliveri and Vecchio, 2016) and antimicrobial (Abouelhassan et al., 2017). According to van Doorn (1997), the bending of gerbera cut flowers was caused by low turgescence of the flower scape when facing water uptake problems. In addition, he notified that bacte- Fig. 1 - Effect of the different preservative solutions (µM) on time of stem bending in gerbera cut flowers. Columns followed by different letters are significantly different at P=0.05. Adv. Hort. Sci., 2019 33(2): 187-195 190 ria in the vase water were the most common cause o f x y l e m b l o c k a g e a f f e c t i n g w a t e r u p t a k e . Accordingly, antimicrobial compounds such as 8- hydroxyquinoline citrate (Elhindi, 2012) and essential oils (Salehi Salmi et al., 2018) were applied to improve vase-life of cut flowers. The effect of the application of MJ on vase life of cut flowers varies widely among species and cultivars. These reports indicated that the ethylene production rate might change with the kind of genes, which were stimulat- ed by MJ (Salimi et al., 2016). The results of the pre- sent study indicated that the decline in the vase life was significantly less in cut flowers in MJ-treated, compared with other treatments. Water loss and water uptake Comparing the results of the different hold-solu- tions revealed statistically significant differences such that the maximum and minimum amounts of water loss, in the 10th day, occurred on cut gerbera hold in 100 µM 8-HQS+ 200 µM MJ and 100 µM 8-HQS+ 100 µM SNP, respectively (Fig. 2). From figure 2 the maxi- mum water loss occurred also on cut gerbera hold in MJ 200 µM alone (together with 100 µM 8-HQS+ 200 µM MJ). Also, data showed that cut flowers treated with 50 and 100 µM 8-HQS; 200 µM SA; 50 and 100 µM SNP; 50, 100, and 200 SA+ 100 µM 8-HQS; 50 µM MJ+ 100 µM 8-HQS; 50, 100, and 200 µM SNP + 100 µM 8-HQS hold solutions lost lower water the control (Fig. 2). The lowest amount of water uptake appeared on 10th day in the cut flowers treated with 100 µM 8- HQS+ 200 µM MJ (Fig. 3). However, there was no sig- nificant difference between this treatment and 50 µM MJ, 200 µM MJ, and 200 µM SNP control treat- ments. In other treatments, water uptake was increased over 10 days of postharvest life in compari- son with control. However, water uptake amounts showed significant differences among hold-solutions such that the maximum amount of it was observed in a cut flower treated with 100 µM 8-HQS+ 100 µM SNP (Fig. 3). Cut flower senescence is closely associ- ated with water uptake stem and RWC of petals, whereas, these characteristics are closely related with the contents of osmoregulation substances such as soluble sugars and soluble proteins (Hou et al., 2018). Soluble carbohydrates of petal Changes of sugars content of gerbera petals are shown in figure 4. Maintenance of elevated total sol- uble carbohydrates content exhibited by the flowers under hold-solutions treatments can be correlated with the delay in senescence and the increase in vase life of Gerbera flowers. The results indicate that treatment with hold-solutions, except the high con- centration of MJ, with or without 8-HQS, caused a significant decrease in reducing sugars compared with the control. Reducing carbohydrate starvation or its symptoms led to unwanted color changes and eventually increased susceptibility to microorgan- isms. Postharvest treatments can reduce carbohy- d r a t e s t a r v a t i o n d u r i n g t h e v a s e l i f e p h a s e . Postharvest treatments like sugar feeding often haveFig. 2 - Relative water loss of cut flower of gerbera in various hold solutions with different concentrations (µM). The indicator was determined on 10st day. Columns fol- lowed by different letters are significantly different at P=0.05. Fig. 3 - Effects of different concentrations (µM) of various hold solutions on the water uptake. The indicator was deter- mined during 10 days. Columns followed by different letters are significantly different at P=0.05. Fig. 4 - Total soluble carbohydrates in petals of hold-solutions- treated and untreated gerbera cut flowers stored at 22°C for 10 days. Hemati et al. - Plant growth regulators as hold solutions of cut-flower Gerbera 191 est amount of carotenoid content among all treat- ments at the end of the experiment. Figure 7 depicts the contents (expressed as mg/g fresh weight) of flavonoid obtained from petals of gerbera cut flowers untreated and treated with hold solution at different concentrations. By comparing untreated-control samples, hold solutions differences could be clearly established (Fig. 7). In particular, the concentrations of petal flavonoid were significantly (p<0.05) higher in treated cut flowers with SNP, SA or MJ; except 50 µM SA, 200 µM MJ, 50 µM SNP treat- ments; than Control. As can be seen, cut flowers treated with 100 and 200 µM SNP+ 100 µM 8-HQS exhibit higher concentrations of flavonoid than the other treatments. Despite the results of this study, most investiga- tions on vase life of cut flowers do not present data on the changes in pigmentation and those that use subjective color grades for evaluation. Browning and discoloration are important factors in determining display quality of cut flowers and in many cases are the major reason for the termination of vase life (Elhindi, 2012; Khalaj et al., 2017; Salehi Salmi et al., 2018). Petal coloration is caused by the accumulation of pigment, including carotenoids, flavonoids, and betacyanins, within epidermal cells. Anthocyanins are synthesized via the phenylpropanoid and flavonoid pathways (Tanaka et al., 2008). Carbon metabolite levels, directly and indirectly, affect almost every metabolic process in a plant life. Anthocyanin and Carotenoid biosynthesis occur concomitantly with sugar accumulation in plant tissue (Hara et al., 2003; Zhang et al., 2015). Similarly, in our study, some vase solutions promoted soluble carbohydrates contents in the petals of gerbera cut flowers (Fig. 4), accompa- nying higher anthocyanin contents and presenting better ornamental quality of petal color (Figs. 5, 6, and 7). It is reported that application of MJ enhanced a positive effect on vase life in general. It seems that 8-HQS, by preventing vascular blockage, caused sug- ars directly to reach flowers in the transpiration stream via xylem. Increased sugar caused by exoge- nous sucrose is well known from earlier studies (Ichimura et al., 1999; Promyou et al., 2012). Han et al. (2018) have illustrated that SNP treatment inhibit- ed significantly the degradation of sucrose of peach fruit at the end of storage. They suggested sugars were significantly affected by SNP treatment proba- bly due to the activities of sucrose metabolism enzymes. Yu et al. (2016) found that MJ treatment could increase the encoding level and enzyme activity of sucrose phosphate synthase, which resulted in the enhancement of sucrose content. Petal pigments The highest concentration of anthocyanin in ger- bera florets was in the SA+ 8-HQS treatments, fol- lowed by the 8-HQS and SA treatments. The MJ, with or without 8-HQS, treatments did not result in a sig- nificant increase in anthocyanin concentration com- pared with that of the control (Fig. 5). Carotenoid content of petals were increased under treatment with all concentrations of SA with or without 8-HQS, all concentrations of SNP with or without 8-HQS, high concentrations of 8-HQS, and all concentrations of MJ with 8-HQS (Fig. 6) while the control had the low- Fig. 5 - Effects of different concentrations (µM) of various hold solutions on anthocyanin content. The indicator was determined during 10 days. Columns followed by diffe- rent letters are significantly different at P=0.05. Fig. 6 - Effects of different concentrations (µM) of various hold solutions on amount of carotenoid. The indicator was determined during 10 days. Columns followed by diffe- rent letters are significantly different at P=0.05. Fig. 7 - Effects of different concentrations (µM) of various hold solutions on flavonoid. The indicator was determined during 10 days. Columns followed by different letters are significantly different at P=0.05. 192 Adv. Hort. Sci., 2019 33(2): 187-195 accumulation of flavonoids in Daucus carota (Sircar et al., 2012). POX activity The POX activity in the petal of gerbera flowers that were treated with different concentrations of all hold-solutions, except 100 µM MJ+ 100 µM 8-HQS, slightly increased during vase life (Fig. 8). The highest activity of POX was observed in cut flowers hold in 50 µM 8-HQS, 100 µM SA, and 200 µM 8-SNP solutions. The enzymatic antioxidant system can work against the accumulation of reactive oxygen species (ROS). Regulation of the antioxidant status and ROS produc- tion by SNP in plant cells subjected to either biotic or abiotic stressors is well established (Vidal et al., 2018). Previously, it has been shown that SNP pro- vides protection in broccoli florets against rapid yel- lowing after harvest (Shi et al., 2016). This study was carried out to provide evidence for the ability of SNP to regulate flower senescence through regulation of the antioxidant status of gerbera petal cells. Salicylic acid can also act as a protector against several stress- ful impacts, scavenge free oxygen radicals, and coun- teract oxidative damage by regulating cellular redox balance and accelerating the transformation of superoxide anion and enhancing the activities of antioxidant enzymes (Zhang et al., 2003). SA treat- ment reduced chilling injury in anthurium via improv- ing the activities of SOD, CAT, and POX (Promyou et al., 2012). Kumar Rai et al. (2018) reported that SA and SNP enhanced tolerance to heat stress in Lablab purpureus, by elevating antioxidant enzyme activity of POX, SOD, and CAT and thus alleviating heat- induced oxidative damage. The present study, for the first time, indicated that SA and SNP treatment delayed the senescence of gerbera flowers via improving the activity of antioxidant enzymes of POX. MJ was reported to stimulate POX activity in banana plants and reduce the level of O2 and H2 O2 (Sun et al., 2013). In this regard, Fan et al. (2016) reported inducing resistance responses in eggplant fruit by increasing the expression of POX genes. Protein There was a significant difference among the type of hold-solution treatments on protein in the 10th day, although the protein content showed no signifi- cant differences among concentrations of a hold- solution. Protein content for SA treatments, with or without 8-HQS, increased compared with the control; however, it was not significantly different from other treatments to control (Fig. 9). The increase observed in the protein content, through treatment with SA, was likely the result of less protein degradation (Alaey et al., 2011) or an increase of protein synthesis (Ezhilmathi et al., 2007). Under flower senescence, the stimulation of protein synthesis leads to protein accumulation that may involve in the enhanced activ- ity of enzymes as a defense mechanism (Promyou et al., 2012). To support the accumulation of proteins due to SA treatment, it was reported that SA results in a pronounced increase in total protein content and the formation of new proteins in roses (Alaey et al., 2011). It seems that MJ by increasing antioxidant defense enzymes leads to maintaining carbohydrate at high levels, as antioxidant inhibits the oxidation of cell biomolecules like proteins and carbohydrates (Kanani and Nazarideljou, 2017). In the present study, different concentrations of SNP and SA, with or without 8-HQS, could markedly increase the con- tents of soluble sugars and soluble proteins, which increased the RWC of petals and water uptake. These increases were helpful in increasing the water retain- ing capacity and also played an important role in increasing vase life of gerbera cut flowers. In addi- tion, Schouten et al. (2018) suggested that SNP enhances flow through xylem vessels by increasing the ionic strength of the vase water. Fig. 8 - Effects of different concentrations (µM) of various hold solutions on activity of POX. The indicator was determi- ned during 10 days. Columns followed by different let- ters are significantly different at P=0.05. Fig. 9 - Petal proteins of gerbera cut flower in various hold solu- tions with different concentrations (µM). The indicator was determined on day 10. Columns followed by diffe- rent letters are significantly different at P=0.05. Hemati et al. - Plant growth regulators as hold solutions of cut-flower Gerbera 193 MDA In the present experiment, a noticeable decrease in the MDA in control treated cut flowers compared with the other vase-solutions (Fig. 10). Accumulation of elevated amounts MDA in control treated cut flower was recorded. This accumulation indicates the presence of oxidative stress in gerbera petals. Zhang et al. (2015) reported over-reduction of the electron transport chain in mitochondria as the main source of O2 production under specific stress conditions. Production of H2O2 can occur during lipid catabolism as a side-product of fatty acid oxidation. ROSs are also involved in the detoxifying reactions catalyzed by cytochromes in both the cytoplasm and the endo- plasmic reticulum (Kumar Rai et al., 2018). Obviously, the observed high activity of POX in SA- and SNP- treated cut flowers are as a protective mechanism against senescence. It has been revealed that MJ mit- igates the ROS effects in maize seedlings subjected to oxidative stress (Ahmadi et al., 2018). 4. Conclusions Treatment with SA+8-HQS extends the vase life of gerbera cut flowers at relatively low SA concentra- tions and leads to generating the maximum cost- effectiveness. In conclusion, our results demonstrat- ed that 8-HQS improves the vase life through increas- ing water uptake and consequently increases total soluble carbohydrates. Also, this effect may be exert- ed by improving the membrane stability and increas- ing proline, antioxidant activity, and pigment con- tents in the presence of SA. 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