Impaginato 311 Adv. Hort. Sci., 2018 32(3): 311-318 DOI: 10.13128/ahs-22302 Postharvest performance of cut rose cv. Lovely Red as affected by osmoprotec- tant and antitraspirant compounds E. Di Stasio, Y. Rouphael (*), G. Raimondi, C. El-Nakhel, S. De Pascale Dipartimento di Agraria, Università degli Studi di Napoli Federico II, Via Università, 100, 80055 Portici (Na), Italy. Key words: β-aminobutyric acid, L-Proline, Rosa spp., stomatal conductance, transpirational flux, water balance. Abstract: In cut flowers, the post-harvest turgor is a critical aspect in a system in which, in the absence of the root system, transpiration water losses must be compensated. Two experiments were conducted in order to elucidate the effect of osmoprotectants (L-Proline) as well as of molecules with antitranspi- rant behavior (ß-aminobutyric acid - BABA or Pinolene) on the water relations and vase life of rose cut stems. Applications of L-Proline enhanced water fluxes, water conductivity, relative water content and stomatal conductance of rose cut stems in comparison to untreated plants, thus increasing the vase-life of rose cut flowers. BABA treatment reduced the stomatal conductance in rose as well as the daily water consumption, on the other hand senescence phenome- na occurred earlier. The water used by pinolene treated stems was lower com- pared to the control and this was associated with a medium increase of the vase life. Overall, enhanced osmoregulation prolonged the vase life of cut flow- ers since the improved water status allowed the cut stem to partially continue its metabolic functions. On the other hand, the control of transpirational flux was functional in maintaining cellular turgor in pinolene treated cut stems, whereas with BABA, senescence phenomena occurred probably due to the acti- vation of biochemical pathway of senescence involving abscisic acid. Taking all together, osmoregulation or direct control of transpirational fluxes may pro- vide a promising avenue for improving the post-harvest longevity of cut roses. 1. Introduction Post-harvest efficiency is a crucial point of the cut flowers commercial value since it is related to growth and storage conditions interacting with the plant genetic background; those aspects will overall contribute to maximize the stems qualitative performance after cutting (Fanourakis et al., 2013). Cut flowers are subjected to a wide range of post-harvest loss- es as developmental senescence, leaf and petal abscission, leaf discol- o rati o n , p rematu re wi l ti n g an d d i sease fro m mo u l d s an d fu n gal pathogens (Scariot et al., 2014). However, among all, water balance is yet a major factor influencing the longevity of cut flowers, in a system in (*) Corresponding author: youssef.rouphael@unina.it Citation: DI STASIO E., ROUPHAEL Y., RAIMONDI G., EL- NAKHEL C., DE PASCALE S., 2018 - Postharvest performance of cut rose cv. Lovely Red as affec- ted by osmoprotectant and antitraspirant com- pounds. - Adv. Hort. Sci., 32(3): 311-318 Copyright: © 2018 Di Stasio E., Rouphael Y., Raimondi C., El- Nakhel C., De Pascale 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 14 December 2017 Accepted for publication 18 April 2018 AHS Advances in Horticultural Science Adv. Hort. Sci., 2018 32(3): 311-318 312 which water losses must be compensated by water uptake and transport in the absence of the root sys- tem (Singh and Moore, 1992; Lu et al., 2010). In particular, the post-harvest life of cut flowers is strongly dependent on their ability to maintain tis- sues hydration overtime, and water deficit or wilting mainly occur if the amount of transpiration exceeds the volume of water uptake (Halevy and Mayak, 1981; van Doorn, 2012). One of the first plant responses to abiotic stress (as for cutting) is the stomatal closure, and this mechanism provides protection against tissues dehy- dration by reducing transpiration from the leaf sur- face (Hare et al., 1998). However, in cut stems stom- ata are not completely closed after cutting, leading to a residual stomatal transpiration that together with cuticular transpiration, determine additional water losses from the stem (van Doorn, 2012). On the other hand, a phenomenon that can severely undermine the cut stems post-harvest performance, is the low- ering of water uptake that is mainly due to occlusions located in the basal stem end (He et al., 2006). In rose, one of the main causes of the cut flower wilting is the vascular occlusion determined by bacteria, air e m b o l i a n d p h y s i o l o g i c a l r e s p o n s e s t o c u t t i n g (Fanourakis et al., 2013). In rose cut flowers, the regulation of water bal- ance has been in the past decades a key aspect in the improvement of the stems vase life (Alaey et al., 2011; Reid and Jiang, 2012). Among several mecha- nisms suggested that may improve water uptake in response to a stress, hydraulic conductivity variations and accumulation of compatible solutes are the most documented (Chen and Murata, 2002; Ehlert et al., 2009). Compatible solutes or osmolytes are organic compounds which help in raising the osmotic pres- sure and thereby maintaining both the turgor pres- sure and the driving gradient for water uptake (Serraj and Sinclair, 2002). Common osmolytes found in plants mainly include proline, trehalose, fructan, mannitol and glycinebetaine and these compounds also help in maintaining the structural integrity of enzymes, membranes and other cellular components during the stress regime (Zhao et al., 2007; Chen and Jiang, 2010). Compatible solutes may be constitutive- ly overproduced in transgenic plants (Zhang et al., 2004) or directly applied on plants to improve stress tolerance under both open-field and protected culti- vation (Okuma et al., 2004; Barbieri et al., 2011; Cirillo et al., 2016). In addition to physiological mechanisms that can be exploited to improve water uptake, the reduction of transpirational flux has traditionally been one of the main objectives for controlling the cellular turgor after harvesting of fresh-cut vegetables and orna- mentals (Prakash and Ramachandran, 2000). The reduction of transpiration can improve the water bal- ance of cut flowers and extend their vase life, where- by artificial closure of the stomata might be an effi- cient strategy to reduce water losses (Lu et al., 2010; van Doorn, 2012). One method of limiting water loss involves the use of antitranspirants, which reduce plant transpira- tion forming a vapour-impermeable film on the leaf surface and, among these, the natural terpene poly- mer di-1-p-menthene (pinolene) is widely applied on different crops (Francini et al., 2011; Abdel-Fattah, 2013). These polymers, also called “Film Forming antitranspirants”, sprayed on crops in a form of water emulsion, are generally employed to reduce weathering and extend pesticide efficacy, improving distribution and adherence of agrochemicals and decrease water loss and wilting of young transplants (Gale and Hagan, 1996; Percival and Boyle, 2009). Research conducted on cut roses revealed that treatments with a Film-forming antitranspirant are able to reduce the degree of fresh weight loss and water loss during transpiration, delay the process of flower opening and slow down the rate of stomatal conductance reduction (Song et al., 2011). Alternatively to traditional antitranspirants, the use of compounds which may induce a series of stress adaptation mechanisms, such as stomatal clo- sure, could also be considered. Beta-aminobutyric acid (BABA) is a non-proteinogenic amino acid known for its ability to increase plant resistance to biotic (Jakab et al., 2001; Baider and Cohen, 2003) and abi- otic stresses (Jakab et al., 2005). Applications of BABA may improve the plant tolerance to stress by activation of defense mechanisms mediated by Abscissic Acid (ABA) and Salicilic Acid (SA) (Zimmerli et al., 2000; Jakab et al., 2005; Baccelli and Mauch- Mani, 2016). Taking this background into considera- tion, it is clear that an efficient control of water bal- ance is crucial to improve cut flowers vase-life and this can be achieved by using molecules that activate water transport in stem or inhibit transpiration. Therefore, the aim of this study was to assess the influence of exogenous applications of osmolytes such as proline or anti-transpiring solutions like β- aminobutyric acid and Pinolene on the water bal- ance, vase-life and also to shed light on the potential Di Stasio et al. - Postharvest performance of cut rose cv. Lovely Red 313 physiological mechanism(s) involved in cut stems of rose. 2. Materials and Methods Plant material and growth conditions Two experiments were carried out in order to assess the effects of exogenous applications of L- Proline (Experiment 1) or antitranspirants [specifical- ly: an active compound film forming (pinolene) and a stomatal closure inducing active compound β- aminobutyric acid ; Experiment 2] on water control in cut stems of rose plants (Rosa spp. L.) cv. Lovely Red. Cut flowers of rose were harvested from two years plants grown in closed soilless system in a heated greenhouse located in Naples, south Italy (40°51’55.5”N 14°20’30.1”E). Rose plants were grown in plastic channels containing pumice and lapillus. The basic nutrient solution was supplied through a drip-irrigation system at a flow rate of 2 L h-1. Irrigation frequency was regularly adjusted dur- ing the growing cycle based on the crop water requirements. At marketable harvest, cut stems were immedi- ately transferred to the laboratory under room con- ditions, re-cut at the base (2-3 cm) and placed in graduated glass cylinders with 300 ml of deionized water and sodium hypochlorite (50 mg L-1). Application of compatible solutes and antitranspi- rants compounds In the first experiment, two days before harvest, rose plants were treated with 10 mM L-1 of L-Proline (Sigma-Aldrich, Saint Louis, Missouri, USA) in 200 ml of deionized water per plant, applied in the growth substrate. Control plants were treated with deionized water only. The treatment was performed at the end of the last daily irrigation and repeated after 24 h. In the second experiment, two days before har- vest and at the end of the last daily irrigation, a sub- strate treatment was performed on rose plants, with of 0.5 mM L-1 of ß-aminobutyric acid (BABA - Sigma- Aldrich, Saint Louis, Missouri, USA) in 200 ml of deionized water per plant, whereas control consisted of plants treated with deionized water. On a second plot of plants, the Pinolene treat- ment was performed in post-harvest once trans- ferred to the laboratory. Stems were sprayed with a solution of 50 g L-1 of Pinolene (96% poly-1-p-men- thene, NU-film, Intrachem bio, Italy) in deionized water. Control stems were sprayed with deionized water only. Storage and physiological measurements Part of the stems, weighted and sized based on length and diameters, were placed on ten precision balances (EK-410i, A&D Instruments Ltd, Abingdon, UK) connected via USB to a computer for automatic monitoring of weight through a specific software (RS- com®, Corby, U.K.). These cylinders were sealed with parafilm to avoid water losses through evaporation. RS-com® software was set to record three daily weights in order to determine stems water consump- tions over storage. Cut stems were stored for 12 days under room conditions measuring daily mean tem- perature and relative humidity using a thermo- hygrometer (DO 9847K, Delta OHM Srl, Padova, Italy). At storage days 2, 4 and 6, water flux measure- ments were recorded by using a Scholander pressure chamber (3005F01 Plant Water Status Console, Soil mosture Equipment Corp., Santa Barbara, California, USA). Twenty centimeter stem segments (5 cm below the calix after measuring stems diameter) were immersed into a cylinder containing distilled water, placed in the pressure chamber, while the other extremity, out of the chamber, was connected to fal- con tubes to collect and weight the water efflux. The system was then subjected to increasing pressure (P= 0.05, 0.1, 0.2, 0.3 MPa) and maintained at each pres- sure value for 5 minutes up to a constant outflow from the stem. Water flux (Jv) was expressed as Jv= kg H2O m -2 s-1 m-1. Water conductivity (Lp) of stems was then expressed by the slope of the regression function of Jv vs. P. Volumes of collected efflux per unit of time (Jv) were normalized to the cutting section surface. Stomatal conductance (gs) was determined at storage days 2, 4 and 6 using a diffusion porometer (Delta P-4, Delta-T Devices, Cambridge, U.K.) in three daily measurements (h 9:00 AM; h 1:00 PM; h 7:00 PM). Osmotic Potential (Yπ) was measured using a dew- p o i n t p s y c h r o m e t e r ( W P 4 , D e c a g o n D e v i c e s , Washington) on frozen/thawed leaf samples. Relative Water Content (RWC) value was calculated as: RWC= (leaf fresh weight - leaf dry weight)/(leaf saturated weight - leaf dry weight) (Morgan, 1984). Leaf area was estimated by scanning cut stems leaves and using the Image J® software (Abramoff et al., 2004) for image processing. The cut stems vase life was assessed visually using a “quality score” from 0 to 4. Statistical analysis All data were statistically analyzed by ANOVA u s i n g t h e S P S S s o f t w a r e p a c k a g e ( S P S S 1 0 f o r Windows, 2001). The RWC data were transformed in Adv. Hort. Sci., 2018 32(3): 311-318 314 arc-sin before ANOVA analysis. 3. Results Experiment 1. Effect of L-Proline application on postharvest performance of cut rose Exogenous applications of L-Proline enhanced sig- nificantly water fluxes of rose cut stems in compari- son to the untreated control, for all the 3 days of measurements (Fig. 1A). During storage, water flux decreased from day 2 to day 6 in treated stems (Fig. 1A). Moreover, stems water conductivity (Lp) was 3.05 [(kg H2O m -2 s-1 m-1) MPa-1] in control and 3.55 [(kg H2O m -2 s-1 m-1) MPa-1] in L-Proline treatment (Table 1). Significant Increase in stomatal conductance (gs) as well as in RWC were observed in L-Proline treat- ment compared to the control (Table 1). Similarly to the physiological measurements, water consump- tions normalized per leaf area were higher in treated stems (Fig. 1B). As a result of cellular osmotic adjust- ment due to L-Proline application, leaf osmotic potential was lower for treated stems in comparison to untreated control (Table 1). The improved water status of L-Proline treated stems influenced positive- ly cut stems longevity extending their vase life by 2 days compared to the untreated control. Experiment 2. Effect of antitraspirants application on postharvest performance of cut rose In our current study, stomatal conductance was reduced by BABA treatment respect to the control (Table 2). Consequently, daily water consumption, normalized per leaf area, was lower for BABA treated stems (Fig. 2B). The application of 0.5 mM of BABA significantly reduced water fluxes during storage (Fig. 2A) as well as the water conductivity (Lp) of rose cut stems (2.6 [(kg H2O m -2 s-1 m-1) MPa-1] in control vs. 1.54 [(kg H2O m -2 s-1 m-1) MPa-1] in BABA treatment). RWC was significantly higher in the control and it decreased during storage (Table 2). Furthermore, the water potential decreased over time and it was lower for rose stems treated with BABA (Table 2). The vase life, however, was not influenced by the treatment since in BABA treated stems the improvement of the water balance was accompanied by premature yel- lowing of the leaves. As a consequence of the mechanical stomatal closure, the water use of pino- lene treated stems was always lower compared to control (Fig. 3). This was associated with a significant increase of the vase life by 1.5 days (Fig. 4). 4. Discussion and Conclusions It is well established that osmotic adjustment con- tributes to maintain water uptake and cellular turgor (Maggio et al., 2002; Heuer, 2003). Among all the osmolytes involved in this process, it has been sug- Fig. 1 - Effect of exogenous L-Proline on water flux (A) and water consumptions per leaf area (B) of rose cut stems during storage. Vertical bars indicate ± SE of means. Table 1 - Effect of exogenous L-Proline on stomatal conductance (gs), relative water content (RWC), osmotic potential (Ψπ) and water conductivity (Lp) of rose cut stems Treatment gs (cm s-1) RWC (%) Ψπ (MPa) Lp (Kg H 2 O m-2s-1 m-1) Control 0.38 b 84 b -0.17 b 3.05 b Proline 0.42 a 89 a -0.34 a 3.55 a Significance * * * * NS,*, not significant or significant at P≤0.05 respectively. Within each column, different letters indicate significant differences. Table 2 - Effect of exogenous β-aminobutyric acid (BABA) on stomatal conductance (gs), relative water content (RWC), osmotic potential (Ψπ) and water conductivity (Lp) of rose cut stems NS,*, not significant or significant at P≤0.05 respectively. Within each column, different letters indicate significant differences. Treatment gs (cm s-1) RWC (%) Ψπ (MPa) Lp (Kg H 2 O m-2 s-1 m-1) Control 0.41 a 79 a -0,17 2.60 BABA 0.25 b 74 b -0,27 1.54 Significance * * * * Di Stasio et al. - Postharvest performance of cut rose cv. Lovely Red 315 gested that proline, exogenously applied via foliar spraying or through the irrigation water, could local- ize into the cytoplasm to reduce the cellular osmotic potential and to restore cellular hydration (Gadallah, 1999; Barbieri et al., 2011). In our experiment, L- Proline treatment on rose plants has shown to sub- stantially improve the hydration state of the cut stems, with an observed decrease of the leaf osmotic potential and increased stomatal conductance and leaf RWC. Consequently, the improved hydration state of tissues and stomatal conductance enhanced the water consumption in plants treated with L- Proline. The decline in stem water conductivity, is one of the main reasons for impaired water balance, as well as water stress is the most common reason for reduced cut roses vase life (Halevy, 1976; Joyce and Jones, 1992). The increase in water fluxes and water conductivity for the L-Proline treated flowers was an evidence of improved water status of the plant tis- sues that probably was the main factor involved in the extended vase life of L-Proline treated stems. It h a s b e e n d e m o n s t r a t e d t h a t , i n c u t f l o w e r s , osmolytes are fundamental compounds in maintain- ing water balance, a key factor to extend their longevity (Ichimura et al., 1997) as well as accumula- tion of these solutes, such as Proline, is one of the main mechanisms to alleviate the detrimental effects of dehydration (Morgan, 1984; Anjum et al., 2011). In fact, the role of osmolytes includes mainly protection against the deleterious effects of the low water activ- ity, preserving appropriate cellular volume (Csonka and Hanson, 1991). However, even though it is not yet clear if an extension of the cut flowers vase life may be more related to the ability of stem to maintain sustained water uptake rates or to control water losses, the control of the stomatal conductance is a fundamental determinant of the tissue water balance (Fuchs and Livingston, 1996; Woodward et al., 2002). In nature, it is well known that plants control water losses by regulating transpiration in response to environmen- tal factors (Chaerle et al., 2005). In some respect, cut flowers respond to the same stimuli and the differ- ence between the rate of water uptake and the tran- Fig. 2 - Effect of exogenous β-aminobutyric acid (BABA) on water flux (A) and water consumptions per leaf area (B) of rose cut stems during storage. Vertical bars indicate ± SE of means. Fig. 3 - Effect of Pinolene on water consumptions per leaf area of rose cut stems during storage. Vertical bars indicate ± SE of means. Fig. 4 - Effect of Pinolene on the vase life of rose cut stems expressed as decay of 50% of the stems quality. Different letters indicate significant differences at P≤0.05, vertical bars indicate ± SE of means. 316 Adv. Hort. Sci., 2018 32(3): 311-318 spiration rate is one of the parameters that will define their hydration state. As documented in different cases, BABA acts through potentiation of ABA-dependent signaling pathways (Ton and Mauch-Mani, 2004) and for this reason, we supposed that applications of ß-aminobu- tyric acid (BABA) may increase the tolerance to water shortage through the induction of functions associat- ed to the synthesis of ABA, such as stomatal closure (Jakab et al., 2001; Desikan et al., 2004). Applied on rose plants, BABA treatment has induced a decrease in stomatal conductance, with the consequent reduction of the stems water con- sumptions. Along with this decrease of the transpira- tional flux, water fluxes and RWC decreased over time and they were generally lower in BABA treated stems. In addition, Lp was lower in BABA-treated stems. The decreased RWC and water potential, together with a reduction of the cut stems hydration state, may be associated to senescence phenomena that occurred with the premature yellowing of the leaves, which is also mediated by ABA (Hunter et al., 2004; Ferrante et al., 2006). Accordingly, Mayak and Halevy (1972) reported that exogenous application of ABA to rose cut flowers accelerate senescence phe- nomena. Another strategy to control the plants transpira- tion and sustain a favorable plant water status is the utilization of antitranspirants compounds (Del Amor and Rubio, 2009). Our results confirmed that film- forming antitranpirants are effective in reducing water losses providing a thin coating on the leaves surfaces leading to an improved tissues water status in cut roses (Moftah and Al-Humaid, 2005; Song et al., 2011; Mikiciuk et al., 2015). Consistently, this mechanical effect on the tran- spirational flux regulation was observed on water consumptions normalized per leaf area rose cut stems, that were significantly reduced by pinolene application during the vase life. The reduced water use was correlated to an extended vase life com- pared to the water-treated control. In conclusion our results demonstrated that both osmoregulation and direct transpirational control were effective strategies in maintaining an enhanced hydration state of rose cut stems, leading to a pro- longation of the stems vase life. Treatment with 10 mM L-Proline has allowed the maintenance of higher stomatal aperture and improved cut stems RWC and Lp during storage. The positive effects on cut stems were measured as decrease of osmotic potential and increased stomatal aperture consequent to osmoreg- ulation. These physiological conditions are crucial for prolonging the vase life of cut flowers because, despite the absence of the root system, allow the stem to partially continue its metabolic functions. On the other hand, the reduction of transpiration that is considered a functional target for controlling cellular turgor after harvest thus prolonging cut flow- ers. Since ABA is involved in the induction of physio- logical mechanisms that facilitate adaptation to abi- otic stress, it has been hypothesized that the admin- istration of BABA, a mediator of ABA functions, may c o n f e r a s t r e s s p r o t e c t i o n t h a t c o u l d r e s u l t i n enhanced turgor and vase life of cut stems. In fact, our results also demonstrated that applications of 0.5 mM BABA on rose has reduced water consumption by inducing stomatal closure. However, this was associated with a more rapid decay of the cut stems quality probably for earlier oncoming of senescence phenomena. 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