Impaginato 371 Adv. Hort. Sci., 2018 32(3): 371-378 DOI: 10.13128/ahs-23266 Postharvest application of hydrogen peroxide and salicylic acid differently affects the quality and vase life of cut rose (Rosa hybrida L.) petals and leaves G. Cocetta, A. Ferrante Dipartimento di Scienze Agrarie e Ambientali, Università degli Studi di Milano, Via Celoria, 2, 20133 Milano, Italy. Key words: chlorophyll fluorescence, cut flowers, elicitors, oxidative stress, phe- nolic compounds, senescence. Abstract: Rose represents an important product in the market of cut flowers. Its quality is related to visual appearance and is affected by oxidative stress and senescence. To maintain the quality and extend the product vase life, innova- tive technical solutions to be applied in postharvest are needed. In this work the effectiveness of hydrogen peroxide (H2O2) and salicylic acid (SA), was assessed on cut rose leaves and petals. Several physiological indicators of quali- ty were studied, including chlorophyll content, chlorophyll a fluorescence, color, lipid peroxidation, phenolic compounds and anthocyanins. After 7 days of vase life 73.33% of untreated roses were not marketable anymore, while the percentage was lower in response to treatments (47.06% in SA and 25.53% in H2O2). The application of H2O2 induced a reduction in leaf chlorophyll and in the performance index which, at the end of the vase life decrease by 76% and 49% respectively. Consistently, the lipid peroxidation in leaves treated with H2O2 increased by a 53%. After 4 days of vase life, SA allowed maintaining high- er levels of anthocyanins in petals compared to H2O2 and to controls. The results obtained allowed individuating different responses, depending on the treatment applied as well as on the plant organ. 1. Introduction The market of cut flowers is characterized by the high perishability of the commercialized products. The pipeline from growers to the final con- sumers, is often long and at the same time, the item must have very high- quality standards. Flowers showing discoloration, shriveling, bending or any other visible sign of damage can no longer be commercialized, and product losses represents a crucial problem for this sector. Rose (Rosa hybrida L.) is one of the most important species in the flower market and it is particularly appreciated by the consumers as cut flower. The quality of cut roses is strictly related to the integrity and quali- ty of petals, but also to the color of leaves, which contributes to their visual appearance. Chlorophyll degradation and leaf yellowing reduce the (*) Corresponding author: giacomo.cocetta@unimi.it Citation: COCETTA G., FERRANTE A., 2018 - Postharvest application of hydrogen peroxide and salicylic acid differently affects the quality and vase life of cut rose (Rosa hybrida L.) petals and leaves. - Adv. Hort. Sci., 32(3): 371-378 Copyright: © 2018 Cocetta G., Ferrante A. 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 23 May 2018 Accepted for publication 6 September 2018 AHS Advances in Horticultural Science Adv. Hort. Sci., 2018 32(3): 371-378 372 ornamental value of cut flowers and compromise their commercialization. During transportation and handling, leaves and petals can undergo mechanical damage, which can lead to tissue browning with neg- ative effect consequences on quality. On the physiological point of view, the loss of quality is a direct consequence of oxidative stress which in turn can lead to senescence (Kumar et al., 2008). These phenomena are characterized by the activation of several physiological responses at cellu- lar level and involve signaling molecules, enzymes, and transcriptional regulators such as genes and transcription factors (Gregersen et al., 2013; Thomas, 2013). In the recent years, several efforts have been made to maintain the quality of cut roses and extend their vase life. These efforts include breeding pro- grams the improvement of growing conditions, and the optimization of transportation. Moreover, the effectiveness of several treatments applied during the vase life has been assessed (Reid and Jiang, 2012). Salicylic acid (SA) is a plant hormone involved in several plants functions, including stress responses, development, and plant signaling (Hayat et al., 2010; An and Mou, 2011; Rivas-San Vicente and Plasencia, 2011). Spray application of SA has been reported to prolong vase-life in cut rose flowers by increasing the activity of the ROS-scavenging enzyme catalase and improving the water balance. Interestingly, the low- est dosage applied (50 µM) was the most effective (Alaey et al., 2007). Also, in other studies, low con- centrations of SA (0.01 mM) have been reported as the most effective in inducing plants responses to stress (Horváth et al., 2007). Hydrogen peroxide (H2O2) is an important mole- cule produced and accumulated in plant cells because of the aerobic metabolism. It belongs to the reactive oxygen species (ROS) and can play a key role in stress metabolism and senescence. The increment in ROS levels is, in fact, a typical feature of senes- cence and can lead to cellular damage and finally to cell death (Panieri et al., 2013). However, slight alter- ations of the ROS balance, including H2O2 accumula- tion, can be considered as important signals in plant cells and can trigger a series of defense responses, which in some case can also involve SA (Kalachova et al., 2013; Herrera-Vásquez et al., 2015). While high concentrations of H2O2, can directly induce oxidative stress in plant tissue, low doses can lead to the acti- vation of positive physiological responses. It has been suggested that H2O2 priming can help in modulating ROS-mediated stress tolerance in plants (Hossain et al., 2005). Non-toxic levels of this molecule must be maintained to have beneficial effects and to improve the quality and vase life of cut flowers, as reported for lily (Liao et al., 2012). The aim of this work was to evaluate the effect of low concentrations of H2O2 and SA when applied to cut roses during the vase life. Attention has been given to the individuation of specific and common responses induced by these two molecules. To achieve this goal, several indices in both petals and leaves were considered, including chlorophyll con- tent, chlorophyll a fluorescence, color, lipid peroxida- tion, phenolic compounds and total anthocyanins. 2. Materials and Methods Plant material Cut rose stems (Rosa hybrida L. ‘Tacazzi’) at the commercial developmental stage were purchased on July 20th, 2017, from the Milan flowers market and brought to the laboratory within one hour. Each stem was around 60 cm-long. Once in the laboratory, 20 stems were randomly selected from a pool of 60 and placed in a beaker filled with 2 L of distilled water (control). Similarly, two other groups of 20 stems each, were placed in a SA (0.01 mM) and H2O2 (0.1 mM) solution respectively. The concentrations of the treatments were chosen among the lowest effective dosage found in the literature to reduce the risk of toxicity. After 24 hours, all the solutions were substi- tuted with 2 L of fresh distilled water and the volume was maintained until the end of the trial. The vase life conditions were: 20±2°C, 55% relative humidity (RH), 18 µmol m-2 s-1 light intensity, with a photoperi- od of 12 hours. Samples of petals and leaves were collected at the beginning of the trial as well as after 4 and 7 days of vase life. After 7 days the remaining stems were maintained until all of them were consid- ered unmarketable. Vase life and damaged flowers (%) At each time point, the number of damaged flow- ers were estimated based on the visual appearance. Those flowers showing wilting, shriveling or desicca- tion were considered as not marketable anymore and thus counted as damaged. This information was used to calculate the percentage of damaged flowers and the average vase life (reported as days). Water content (%) At harvest and after 7 days three roses for each treatment (the whole stem) were weighed and Cocetta and Ferrante - Effect of H 2 O 2 and salicylic acid on cut rose vase life 373 immediately placed in an oven at 115°C until the complete drying. The water content was calculated as percentage of water respect to fresh weight. Chlorophyll and chlorophyll a fluorescence-related parameters During vase life in vivo determination of leaves chlorophyll content was performed using a CL-01 chlorophyll mater (Hansatech, United Kingdom). Similarly, chlorophyll a fluorescence was measured on dark adapted leaves using a portable fluorimeter (Handy PEA, Hansatech, United Kingdom). The para- meters measured were: the quantum maximum effi- ciency of PSII (Fv/Fm), the performance index (PI), the number of reactive centers per cross section (RC/CSm), and the amount of energy dissipated per reaction center (DIo/RC). Color measurement Changes in petal coloration in response to treat- ments and to vase life were evaluated at each time point by using a Minolta CR-400 colorimeter (Konica Minolta, Inc., Japan). The color parameters were described using the Lab* and the Munsell (L*C*h) color spaces. Briefly, in the Lab*color space the light- ness is represented by L* (with 0 indicating black and 100 white). The colors in the red green region are represented by a* (red with positive values and green with negative values) while b* describes the interval from yellow (positive values) to blue (nega- tive values). In the Munsell color space h represents the hue while C* is the chroma (or color purity). Phenolic index and total anthocyanins For the extraction of phenolic compounds and anthocyanins, around 1 g of petals and leaves, col- lected at each time point, were homogenized in 8 mL of acidified methanol (1% HCl V/V) and extracted overnight in the dark. The phenolic index was calcu- lated as the absorbance at 320 nm of the diluted extracts, normalized to fresh weight (Ke and Saltveit, 1989). Total anthocyanins were determined spec- trophotometrically at 535 nm using an extinction coefficient (ε) of 29,600 mM-1 cm-1 and expressed as cyanidin-3-glucoside equivalents and (Klein and Hagen, 1961). Lipid peroxidation The level of lipid peroxidation was measured with the thiobarbituric acid reactive substances (TBARS) assay (Heath and Packer, 1968). Briefly, around 1 g of petals and leaves was homogenized in 5 mL 0.1% trichloroacetic acid (TCA) solution. The extract was mixed with 4 mL of 20% (W/V) TCA, 25 µL of 0.5% thiobarbituric acid (TBA) and distilled water. After vortexing, the mixture was heated at 95°C for 30 minutes in a water bath and then cooled on ice. Absorbance at 600 nm was subtracted from the absorbance at 532 nm (as an index of non-specific turbidity) and the concentration of TBARS was expressed as malondialdehyde (MDA) equivalents (nmol g-1 FW), calculated using an extinction coefficient (ε) of 155 mM-1 cm-1. Statistical analysis All data were subjected to two-way ANOVA fol- lowed by Bonferroni’s multiple comparisons test, except for vase life data which were subjected to a one-way ANOVA. Statistics were performed using GraphPad Prism version 6 for Windows, GraphPad Software, La Jolla, California, USA (www.graphpad. com). 3. Results Vase life and water content After 4 days of vase life all the flowers treated with H2O2 and SA were considered marketable, while 10% of untreated flowers showed a marked loss of quality. After 7 days, the higher rate of damage was recorded in the controls (73.33%), followed by SA (47.06%) and H2O2 (25.53%) (Fig. 1 A). After 8 days all Fig. 1 - Percentage of damaged flowers (A) and average vase life (B) measured in cut ‘Tacazzi’ rose. Data are means ± SE (B: n=14; C: n=3). Different letters indicate significant dif- ferences (p<0.05). Adv. Hort. Sci., 2018 32(3): 371-378 374 the control flowers were already damaged, while 6 flowers treated with SA were still marketable until 10 days, and 6 among those treated with H2O2 lasted until 12 days. The treatment with H2O2 determined a significant increment in the average vase life compared to SA and control (Fig. 1 B). The initial water content was 77.86% and showed a slight progressive decline without any significant difference among the treatments. After 7 days the values were: 70.01%, 70.61%, 70.64%, in control, SA and H2O2 respectively. The flowers treated with H2O2 showed a reduced opening compared to those treat- ed with SA or to controls (Fig. 2 A, C). Color After 7 days of vase life, all the petal samples looked paler compared with to the beginning of the trial and an increment in the L* value was recorded despite the treatments applied (Table 1). H2O2-treat- ed flowers did not show any change in the color- related parameters compared to controls. On the other hand, after 7 days, SA induced a decrement in all the color attributes compared to the beginning of the trial, including a*, b*, hue (h) and chroma (C*). This variation was consistent with the visual observa- tion of the petals which appeared darker and turned from red to a more violet coloration (Fig. 2 C). Chlorophyll content and chlorophyll a fluorescence- related indexes Treatment and vase life duration significantly affected the chlorophyll content of cut rose leaves. After 4 days of vase life, the chlorophyll content was Fig. 2 - Visual appearance of cut roses (cv. Tacazzi) as affected by H 2 O 2 or SA application after 4 (A, B) and 7 (C) days of vase life. Cocetta and Ferrante - Effect of H 2 O 2 and salicylic acid on cut rose vase life 375 tionality after 7 days of vase life, evidenced by a sig- nificant decrement in the PI value (Fig. 3 C). No signif- icant changes were observed in Fv/Fm, RC/CSm and in DIo/RC (Fig. 3 B, D, E), even though these indexes showed a trend similar to the one observed in the PI. Lipid peroxidation The level of lipid peroxidation in leaves was signif- icantly affected by treatment and by vase life dura- tion. In leaves treatments induced higher oxidative damage compared to control, already after 4 days Fig. 3 - Chlorophyll content (A) and chlorophyll a fluorescence-related indexes: maximum quantum efficiency of PSII (Fv/Fm) (B), perfor- mance index (PI) (C), number of reaction centers per cross section (RC/CSm) (D), energy dissipated per reaction center (DIo/RC) (E). Measurements were conducted on leaves of cut ‘Tacazzi’ rose. Data are means ± SE (n=6). Different letters indicate signifi- cant differences (p<0.05). significantly lower in the controls and in SA-treated leaves compared to H2O2-treated ones. However, H2O2 induced a pronounced discoloration of leaves, particularly at the end of the trial (Fig. 2 B, C). This observation is confirmed by the significant reduction in chlorophyll content which has been recorded after 7 days of vase life (Fig. 3 A). All the parameters related to chlorophyll a fluo- rescence showed a trend consistent with the one observed in chlorophyll content. In particular, stems treated with H2O2 showed a loss in the leaf PSII func- Data are means ± SE (n=6). Different letters indicate significant differences (p<0.05). Table 1 - Changes in petal color parameters of cut ‘Tacazzi’ rose during vase life and in response to treatments Treatment Days of vase life L* a* b* h C* - 0 41.17±0.64 a 55.93±0.31 a 14.10±.01 a 14.14±0.98 a 57.70±0.37 a Control 4 34.13±1.93 a 48.57±1.89 ab 9.75±1.12 ab 11.29±1.05 ab 49.56±2.00 ab H 2 O 2 0.1 mM 4 39.00±2.16 a 49.08±1.69 ab 10.46±2.13 ab 11.81±2.09 ab 50.77±2.30 ab SA 0.01 mM 4 36.09±1.18 a 50.09±1.78 ab 10.12±1.94 ab 11.21±1.77 ab 51.17±2.11 ab Control 7 47.73±3.02 b 48.12±2.83 ab 9.45±0.56 ab 11.16±0.63 ab 49.05±2.84 ab H 2 O 2 0.1 mM 7 51.12±1.22 b 50.13±1.67 ab 9.80±0.99 ab 11.00±0.81 ab 50.97±1.78 ab SA 0.01 mM 7 50.19±2.67 b 44.57±3.14 b 6.49±1.02 b 8.52±1.64 b 45.10±3.04 b 376 Adv. Hort. Sci., 2018 32(3): 371-378 and lipid peroxidation reached the maximum level in H2O2-treated leaves after 7 days of vase life (Fig. 4 A). The amount of MDA equivalents was markedly high- er in flowers (Fig. 4 B) compared to leaves, but no sig- nificant changes were observed in petals in response to vase life or to treatments. Phenolic index and total anthocyanins The levels of total phenolic compounds, estimated with the phenolic index, were stable, with similar val- ues between leaves and flowers and without showing any significant change in response to treatment or to vase life (Fig. 5 A and B). On the other hand, total anthocyanins, which were highly accumulated in petals, progressively declined during the vase life (Fig. 5 C and D), with a significant effect of vase life time in both leaves and petals. This trend was more pronounced in petals, which showed a significant decrement already after 4 days in controls and in response to H2O2 treatment. Fig. 5 - Changes in the phenolic index (A: leaves; B: petals) and in total anthocyanins levels (C: leaves; D: petals) of cut ‘Tacazzi’ rose during vase life and in response to treatments. Data are means ± SE (n=3). Different letters indicate significant differences (p<0.05). Fig. 4 - Changes in lipid peroxidation in leaves (A) or petals (B) of cut ‘Tacazzi’ rose during vase life and in response to treatments. Data are means ± SE (n=3). Different letters indicate significant differences (p<0.05). 377 Cocetta and Ferrante - Effect of H 2 O 2 and salicylic acid on cut rose vase life Then again, after 4 days SA-treated petals showed significantly higher levels of anthocyanins compared to H2O2 and to control. 4. Discussion and Conclusions The results obtained in this work allowed individu- ating independent ways of action for the two treat- ments and evidenced positive and negative aspects of both molecules. As a first consideration is important to observe that both treatments determined a reduction in the product losses compared to control and in case of H2O2, a significant extension of the vase life. This pos- itive result is consistent with other previously pub- lished works (Gerailoo and Ghasemnezhad, 2011; Liao et al., 2012). It is also interesting to point out that the two treatments applied, induced different responses in rose leaves and petals. The application of H2O2 determined a delay in the flower opening compared to control and to SA, this is consistent with what already observed in cut lily (Liao et al., 2012) and in tree peony (Shi et al., 2015), and can have positive implications in the postharvest management of cut roses. In fact, the possibility of modulating or delaying the flower opening could be successfully be used to extent the commercial life of cut flowers and to better manage the storage and transportation. Moreover, H2O2 helped in maintain- ing low levels of MDA in petals during the first days of vase life. As a drawback, H2O2 induced leaves yel- lowing which in turn can affect the visual appearance of the stem. The detrimental effect of H2O2 on leaves has been confirmed by the marked loss of chlorophyll and by the higher level of peroxidation recorded at the end of the vase life. The parallel decrement in the PI, suggests a possible positive association between chlorophyll a fluorescence and plant stress, as previ- ously reported (Kalaji et al., 2006). Considering the results obtained in this trial, it appears that H2O2 is not affecting the accumulation of phenolic com- pounds and pigments in cut ‘Tacazzi’ rose. It is known that the effect of H2O2 depends on the dosage (Liao et al., 2012), thus it is possible that the concentration of H2O2 applied in this trial was enough to induce oxidative stress and damage in the leaves while having a positive effect on flowers. There are not many reports about the effect of SA in ornamental leaves, however recently, a role for SA in extending the vase life of Acacia holosericea foliage has been suggested (Chen and Joyce, 2017). The positive effect of SA on the leaves of cut roses has been confirmed in the present work, since at the end of the trial, SA-treated leaves showed a better maintenance of chlorophyll and leaf functionality indexes compared to controls and to H2O2-treated stems. The positive effect of SA could be due to the activation of plants defenses against ROS, including the increment in antioxidant compounds and the activation of antioxidant enzymes. Treatments with SA have been reported to reduce lipid peroxidation in gladiolus cut flower spikes (Rahmani et al., 2015). Also, SA alone or in combination with sucrose, was shown to affect the rate of lipid peroxidation (MDA) and chlorophyll content in carnation petals (Kazemi et al., 2011), but different results were observed depending on the dosage applied. Unexpectedly, in the present work, the application of 0.01 mM of SA was not effective in preventing lipid peroxidation of cut roses, perhaps because of the too low concentra- tion applied. The degradation of anthocyanins is a typical phe- nomenon which negatively affects the quality of ornamental flowers, including rose (Luo et al., 2017). The role of exogenous SA in stimulating the biosyn- thesis of anthocyanin pigments has been document- ed (Ram et al., 2013), thus it can be hypothesized that SA treatment could delay the degradation of pig- ments in petals. The increase of phenolic compounds as well as the anthocyanins content could help in counteracting the senescence and extend the flower life as observed in model plants (McNish et al., 2010). Despite the low dose applied, SA helped in maintain- ing higher levels of anthocyanins in cut rose petals after 4 days of vase life. Also, the petal coloration was affected by SA after 7 days. In conclusion, the negative effect of H2O2 in leaves compared to the beneficial effect observed in flowers is controversial and it would surely worth to be inves- tigated further. Perhaps the negative effects could be circumvented by testing other forms of application, such as direct spraying on the petals avoiding contact with leaves. The application of SA did not induce any damage, but at the same time, the positive effects were not as evident as expected compared to untreated control. This suggests that the conditions of treatment with SA can be further perfectioned. In future experiments the application of higher doses of SA could intensify the positive effects observed in this trial. 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