Effect of Plant Hormones and Preservative Solutions on Post-Harvest Quality and Physiological Senescence Parameters of Cut Leaves of Hosta Tratt. ‘Krossa Regal’ and Polygonatum multiflorum (L.) All. ‘Variegatum’

Abstract

In recent years, there has been growing interest in the use of native ground-grown perennials in floral compositions as cut greenery. The easily available plant materials that can replace some exotic species include Hosta leaves and the leafy shoots of Polygonatum multiflorum. Their vase life should be at least as long as that of the flowers, with which they are combined. In order to prolong the vase life of cut greenery, the conditioning of cut plant material in solutions of plant hormones (GA3 and BA) and commercial conditioning substances (8HQC and Chrysal Clear 2) is most commonly performed. The aim of this study was to evaluate the effect of different conditioning solutions on vase life and parameters indicating the progression of the senescence of plant materials. Cut Hosta leaves and leafy shoots of Polygonatum multiflorum were conditioned immediately after cutting for 24 h in aqueous solutions of benzyladenine (BA) and gibberellic acid (GA₃), 8HQC standard medium with the addition of 2% sucrose and 1% Chrysal Clear 2 solution. The post-harvest storage and physiological senescence parameters of the plant materials were analyzed using the following indicators: the vase life, the relative water content (RWC), electrolyte leakage (E_L), and thiobarbituric acid reactive substance (TBARS) and pigment contents (chlorophyll a, chlorophyll b, carotenoids, and anthocyanins). Conditioning Hosta leaves in a BA solution at 100 mg L⁻¹ immediately after cutting more than doubles their post-harvest vase life. The longevity of P. multiflorum shoots can be effectively extended by storage in a BA solution of 400 mg L⁻¹, for 24 h. Both the plant materials responded to the progressive aging process with the disruption of water management, a reduction in cytoplasmic membrane integrity, and a decrease in the plant pigment content. Tissue water retention in the Hosta leaves was most favorably affected by conditioning in the GA₃ solution at a concentration of 400 mg L⁻¹. The P. multiflorum shoots responded with tissue water retention to conditioning in 1% Chrysal Clear 2 solution. The conditioning of Hosta leaves in BA solution at 400 mg L⁻¹ stabilized the cytoplasmic membranes and inhibited E_L most effectively. In P. multiflorum, the lowest E_L level was found as an effect of conditioning the shoots in GA₃ solution at 200 mg L⁻¹. The degradation of assimilation pigments was prevented by conditioning the Hosta leaves in GA₃ solution at 200 mg L⁻¹ and the P. multiflorum leafy shoots in GA₃ solution, regardless of the concentration used. Although the prolongation of the vase life of the cut leaves and the shoots by up to 30 days was achieved, along with an improvement in the appearance of the plant materials, it was not possible to identify a single conditioner that had a positive effect on all the parameters studied.

1. Introduction

In recent years, an increase in the assortment of floricultural plants has been seen. A new trend that is becoming apparent is the replacement of exotic species with cheaper, more accessible plants that can be grown in an open field and are thus economically justifiable. The leaves of perennial plants, such as Hosta Tratt., Bergenia Moench, Heuchera L., Limonium latifolium (Sm.) Kuntze, and many others, are gaining popularity [1,2].

Polygonatum multiflorum (L.) All. (Figure 1) is a perennial plant belonging to the Asparagaceae family. Its natural habitats include Europe, eastern Asia, the Himalayas, Siberia, and North America. In Poland, it is commonly found in beech and hornbeam forests, as well as in thickets and riverine forests. It is characterized by minimal environmental requirements, preferring shady places and alkaline or weakly acidic clay soils [3,4]. P. multiflorum is a plant of great ornamental value; its leafy stems grow to a length of up to 0.80 m and are characteristically curved at the top of the shoot. The leaves are ovate-elliptical in shape, dark green on the upper side of the leaf blade and blue green on the underside, reaching up to 15 cm in length, and are arranged twistily on the stem. The leaves are pointed and sharp-edged, with clearly visible venation [3,5].

Hosta Tratt. (Asparagaceae) (Figure 2) is considered one of the most popular perennial species that is grown in gardens as an ornamental plant due to its exceptionally decorative foliage [6]. The cultivation of Hosta is relatively simple due to its minimal environmental requirements, with a preference for humus-rich, moist soil. Typically, Hosta should be well exposed to sunlight, but the plants can also grow in shade and semi-shade conditions. Hosta Tratt. ‘Krossa Regal’ is a cultivar characterized by a height of up to 0.90 m and a spread of up to 1.50 m. The leaves are large (28/18 cm), lanceolate in shape, and blue-green in color, with prominent venation [6].

Cutting the leaves from the parent plant triggers biochemical and physiological changes in their tissues. These initiate the aging process, referred to as the final stage of their development [7,8]. The first visual sign of the ongoing aging of cut plant material is chlorophyll degradation, manifested as the yellowing of the leaves [9]. The other visible changes include disturbances in the water balance, resulting in a decrease in leaf mass and an increase in reactive oxygen species (ROS) levels [10,11]. The consequence of these processes is the loss of the integrity of cytoplasmic membranes, a decrease in the activity of enzymes of the antioxidant system, and an increase in the activity of proteases and nucleases, resulting in the death of the leaf tissue [12,13]. The pace of the senescence of cut foliage is strongly influenced by the environmental conditions during the storage of cut plant material, including temperature, water supply, and duration of low light/darkness [14].

The delaying of cut plant material aging is one of the key challenges faced by producers and distributors of flowers and cut greens [14,15]. Among the ways to prolong the life of cut greens, the conditioning of cut leaves or foliaged stems is the most commonly mentioned. This method involves placing the cut plant material in a chemical solution immediately after cutting. Conditioning usually takes between 4 and 24 h [16]. Choosing the right conditioning substance is not easy, as its effectiveness varies depending on the species and even on the variety [17]. The available literature lists gibberellic acid (GA₃), hydroxyquinoline esters, and benzyladenine (BA) as the most commonly used conditioning substances, together with various commercial products specially designed to extend the vase life of cut flowers [1,18,19].

Hosta Tratt. ‘Krossa Regal’ and Polygonatum multiflorum (L.) All. ‘Variegatum’, represent a species with fairly minimal environmental requirements, with simple cultivation technologies in temperate climate conditions. They are distinguished by their highly decorative leaves that can replace the leaves of exotic plants currently used in floristic compositions [5,20,21]. Therefore, the aim of the current study was to evaluate the effectiveness of several conditioning solutions containing different concentrations of GA₃, BA, as well as 8-hydroxy quinoline citrate + 2% Saccharose (8HQC + 2%S) and the commercial preparation Chrysal Clear 2 in prolonging the vase life of cut Hosta and P. multiflorum leaves. The post-harvest longevity of the leaves was assessed throughout the experiment, as well as parameters related to the biochemical and physiological changes occurring in the senescent leaves, including the amounts of assimilation pigment and anthocyanin, the relative tissue water content (RWC), and the degree of damage to the cytoplasmic membranes (E_L, TBARS).

2. Materials and Methods

2.1. Plant Material

The plant material used for the experiment consisted of the leafy shoots of Polygonatum multiflorum (L.) All. ‘Variegatum’ and the leaves of Hosta Tratt. ‘Krossa Regal’ obtained from didactic field collection at the experimental farm of the Department of Ornamental Plants and Dendrology of the University of Life Sciences in Lublin. Mature shoots and leaves without visible signs of mechanical damage or symptoms of pathogen attack were subjected to analysis. The shoots and leaves were cut in the morning and placed directly into containers with distilled water. As soon as possible, under the best possible thermal conditions, the material was transported to the Department of Botany and Plant Physiology of ULSc in Lublin. The conditioning of the shoots and the next stage of the experiment took place in a vegetation room.

2.2. Experimental Procedure

The experiment was conducted under controlled thermal and light conditions: temperature 21°/18 °C (day/night), relative humidity 60%, quantum radiation intensity 190 µmol m⁻² s⁻¹, with a diurnal rhythm of 12 h light, 12 h dark. The experiment consisted of nine combinations of 20 leafy shoots or leaves each, individually labelled and treated as replicates. Immediately after pruning to equal length, the plant material was conditioned for 24 h in aqueous solutions of benzyladenine (BA) and gibberellic acid (GA₃) at concentrations of 100, 200, and 400 mg L⁻¹, 8HQC standard medium with 2% sucrose (8HQC-200 mg L⁻¹ + 2%S) and 1% Pokon & Chrysal’s Chrysal Clear 2 solution. After conditioning, the shoots were transferred to containers with distilled water, which was changed daily until the end of the experiment. The control consisted of untreated shoots kept in distilled water for the entire duration of the experiment.

2.3. Chemical Measurements and Analyses

The post-harvest vase life of the cut greens was determined by noting the number of days from harvest to the first signs of decorative loss based on external appearance. The moment of the loss of decorativeness was determined using the following measures:

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Leaf blade discoloration—yellowing (the gradual loss of chlorophyll and emerging leaf chlorosis);

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The browning of leaf margins and the appearance of necrotic spots;

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The drying of the leaf blade and the curling of the margins;

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Leaf drops from the stems.

The leaves or leafy shoots were removed from the experiment when 30% of the leaves on the stem or 30% of the leaf blade showed the above-mentioned changes.

The relative water content (RWC) of the leaf tissues was determined by the method of Barrs [22] according to this formula:

$$\mathrm{R}\mathrm{W}\mathrm{C}=\left({\mathrm{W}}_1/{\mathrm{W}}_2\right)\times 100\%,$$

where W₁—current tissue water content; W₂—water content of tissues when fully saturated with H₂O.

The degree of damage to the cytoplasmic membranes was assessed by determining electrolyte leakage (E_L) from the tissues according to the method of Kościelniak [23]. Ten 0.9 cm diameter discs were cut from the leaves, and then inundated with 20 cm³ of redistilled water and shaken for 24 h at room temperature. The first measurement of electroconductivity (K₁) was then taken using a microcomputer conductivity meter type CC-317 from Elmetron. Next, the plant material was held for 15 min in a water bath at 90 °C, and after a further 24 h of shaking, electroconductivity was measured again, obtaining the total electrolyte content (K₂). Electrolyte leakage was presented as a percentage of their total content in the tissue according to this formula:

$${\mathrm{E}}_{\mathrm{L}}=\left({\mathrm{K}}_1/{\mathrm{K}}_2\right)\times 100\%$$

Cytoplasmic membrane damage was also assessed by determining the thiobarbituric acid reactive substance (TBARS) content indicative of the degree of membrane lipid peroxidation according to the method of Heath and Packer [24]. A total of 250 mg of plant material was homogenized in the presence of 0.1 M potassium phosphate buffer, pH = 7.0. The samples were then centrifuged for 20 min at 12,000 rpm. The reaction mixture contained 2 cm³ of 0.5 per cent TBA (thiobarbituric acid) in 20 per cent TCA (trichloroacetic acid) and 0.5 cm³ of extract. Absorbance was determined at 532 and 600 nm using a Cecil CE 9500 spectrophotometer. TBARS levels are expressed in nanomols per 1 g fresh weight.

The content of assimilation pigments (chlorophyll a, chlorophyll b, and carotenoids) in the leaves was determined by extracting a defined amount of fresh leaf mass with 80% acetone and measuring absorbance at three wavelengths (λ), 470 nm (carotenoids), 646 nm (chlorophyll b), and 663 nm (chlorophyll a), using a Cecil CE 9500 spectrophotometer. The pigment content was recalculated according to the method described by Lichtenthaller and Wellburn [25] using this formula:

$${\mathrm{C}}_{\mathrm{chl}.\mathrm{a}}=12.21 \times {\mathrm{A}}_{663}-2.81 \times {\mathrm{A}}_{646}$$

$${\mathrm{C}}_{\mathrm{chl}.\mathrm{b}}=20.13 \times {\mathrm{A}}_{646}–5.03\times {\mathrm{A}}_{663}$$

$${\mathrm{C}}_{\mathrm{car}}=(1000\times {\mathrm{A}}_{470}-3.27\times {\mathrm{C}}_{\mathrm{chl}.\mathrm{a}}-104\times {\mathrm{C}}_{\mathrm{chl}.\mathrm{b}})/227$$

where A_λ—absorbance value at wavelength λ.

The anthocyanin content in the leaves was determined according to the method of Leng and Qi [26]. A total of 0.5 g of plant material was extracted in a mixture of methanol and HCl (99:1, v/v) and kept for 24 h at 4 °C in the dark. The samples were then centrifuged at 12,000 rpm for 10 min. Absorbance was measured at two wavelengths (λ), 527 and 625 nm, using a Cecil CE 9500 spectrophotometer. The concentration of anthocyanins in the plant material was calculated using the molecular extinction coefficient of cyanidin-3-monoglucoside (29,600 mol cm⁻¹) and taking into account the molecular weight of the compound (445 M) and the sample dilution. The pigment content is given in μg g⁻¹ fresh weight.

2.4. Statistical Analysis

All analyses and measurements were performed with five replicates after 14 and 28 days of storing the plant material in distilled water. All the results in the tables were statistically analyzed using Statistica 10; the significance of differences are shown using Duncan’s confidence intervals at p = 0.05.

3. Results

Hosta foliage post-harvest longevity was most effectively prolonged by conditioning in BA and GA₃ solution at a concentration of 100 mg dm⁻³ (the prolongation of decorativeness by 16 and 13 days, respectively, compared to that of the control) (Figure 3). BA was the most effective of the solutions used for extending the vase life of the leafy shoots of P. multiflorum when applied for 24 h conditioning at a concentration of 400 mg L⁻¹ (extending vase life by 17 days compared to that of the control). A long vase life (30 days) was also observed for the shoots conditioned in an aqueous solution of BA and GA₃ at a concentration of 200 mg L⁻¹.

The analysis of shoot hydration showed that the relative water content (RWC) decreased with the duration of storage (Figure 4). In the analysis of the water content of the P. multiflorum leaves after 14 days of storage, the highest value of the RWC index was found in the variant in which the leafy shoots were conditioned in a solution of GA₃ (200 and 400 mg L⁻¹), 8HQC + 2%S, and Chrysal Clear 2. Analysis performed after 28 days of the experiment showed the most beneficial effect of GA₃ at the two higher concentrations and Chrysal Clear 2. After 14 days of the experiment, the highest value of the relative water content index in the Hosta leaves was recorded in the variant in which leaves were conditioned at all the applied concentrations of BA, GA₃ 400 mg L⁻¹, and in the Chrysal Clear 2 solution. On the other hand, after 28 days of the experiment, the highest value of RWC was recorded in the variant in which leaves were conditioned in GA₃ solution at a concentration of 400 mg L⁻¹.

The statistical analysis of the results obtained after 14 and 28 days of the experiment showed that the permeability of the cytoplasmic membranes of the P. multiflorum and Hosta leaves, expressed in values of the E_L and TBARS indices, increased with advancing senescence (Figure 4). The most effective effect on the inhibition of cytoplasmic membrane degradation was achieved by conditioning the leafy shoots of P. multiflorum in a solution of 8HQC + 2%S (reduction in E_L efflux by 25.8% compared to that of the control). A significant decrease in the value of this parameter was determined in the leaves conditioned in BA 200 mg L⁻¹ and GA₃ 100 mg L⁻¹ solutions (by 21.4% and 21.3%, respectively, compared to those of the control). The results obtained after 28 days of the experiment did not show statistically significant changes in E_L due to the conditioning of the P. multiflorum shoots. The value of the TBARS index measured after 28 days of the experiment was lower in the leaves conditioned in BA solution at concentrations of 100 and 200 mg L⁻¹. After 28 days of the experiment, the most beneficial effect on the inhibition of cytoplasmic membrane degradation of BA at concentrations of 400 and 100 mg L⁻¹ and GA₃ at a concentration of 100 mg L⁻¹ was found, as expressed by the E_L value (decreases in values of 43.7; 36.2; and 33.3%, respectively, compared to those of the control). On the other hand, the lowest TBARS value was found in the variants in which the leaves were conditioned in BA and GA₃ solutions at the lowest concentrations used (decreases of 62.4 and 61.1% compared to those of the control).

The storage of the cut shoots of P. multiflorum resulted in a decrease in the contents of chlorophyll a and b and anthocyanins in the leaves, while it did not affect the content of carotenoids (Figure 5). The analysis of the results showed that all the conditioning substances used in the experiment inhibited pigment degradation more in the P. multiflorum leaves compared to the control variant. The highest contents of chlorophyll a and b determined after 28 days of the experiment were found in the leaves conditioned in BA solutions at a concentration of 400 mg L⁻¹ and across all the GA₃ concentrations. The highest content of anthocyanins was found in the variant in which the leafy shoots of P. multiflorum were conditioned in Chrysal Clear 2 solution, which resulted in the smallest decrease in the content of pigments by 14.5% compared to the control. The quantification of plant pigments in the Hosta leaves showed a decrease in chlorophyll a and anthocyanins that correlated with the duration of the experiment (Figure 6). All the conditioning substances used in the experiment significantly inhibited the degradation of chlorophyll a and b in the Hosta leaves, which was confirmed by analysis performed after 14 and 28 days of the experiment. The content of carotenoids in the leaves of the species under study, after 28 days of the experiment, was found to be significantly higher in all the variants of the experiment compared to the control. However, the anthocyanin content was highest in the variants in which the Hosta leaves were conditioned in solutions of 8HQC + 2%S and Chrysal Clear 2 immediately after leaf cutting.

4. Discussion

In contemporary floral compositions, green additions are a very important element, as they no longer act as mere fillers, but in fact become a significant decorative item that defines the whole plant arrangement [18]. Furthermore, the emerging trend in which cut leaves and stems are used as the only components of a plant decorative composition creates a need to make them last as long as possible. The aging process of the cut plant material and the associated loss of decorative value occurs at different rates depending on the species and often even on the plant variety [27,28]. The vase life of cut plant material depends on many factors, including the growth conditions of the parent plant, the environmental conditions during the storage and marketing of the plant material, and the treatments applied immediately after harvest. In order to increase the longevity of cut plant material, conditioning in solutions of plant hormones or preservatives is a commonly used procedure [18]. Cytokinins and gibberellins are considered to be inhibitors of senescence, and their content in plant tissues decreases as the process progresses [28]. One of the most used plant hormones with proven vase life-prolonging effects on cut plant material is gibberellic acid (GA₃). It has been proven to have a positive effect on extending the post-harvest longevity of the leaves of Alstroemeria aurantiaca [29,30,31], Arum italicum [32], Convallaria majalis [33], Hippeastrum x hybridum [34], Lilium sp. [35], and Zantedeschia aethiopica [36]. Also, cytokinins, including benzyladanine (BA), have a proven inhibitory effect on the aging process of different plant parts, including cut leaves and shoots. This effect was reported for Arum italicum [32]. In the experiment conducted by our team, the beneficial effect of conditioning in GA₃ and BA solutions on the extension of the vase life of cut Hosta leaves and leafy shoots of P. multiflorum has also been confirmed. The Hosta leaves conditioned in GA₃ solution at a concentration of 100 mg L⁻¹ and BA solution at concentrations of 100 and 400 mg L⁻¹ showed the longest post-harvest decorativeness, while the P. multiflorum leaves showed the greatest post-harvest longevity as a result of conditioning in GA₃ solution at a concentration of 200 mg L⁻¹ and BA solution at concentrations of 200 and 400 mg L⁻¹. The positive effect of conditioning leafy shoots of P. multiflorum in GA₃ solution at a concentration of 100 mg L⁻¹ was confirmed in an experiment conducted by Krzymińska-Bródka and co-authors [5]. On the other hand, a study by Wachowicz and co-authors [20] showed that conditioning Hosta leaves in 0.1 mM BA extended their vase life to more than 30 days, confirming the beneficial effect of this cytokinin on the longevity of cut leaves. The conditioning solutions used in the experiment, 8HQC + 2%S in the case of the Hosta leaves and Chrysal Clear 2 in the case of the leafy shoots of P. multiflorum, did not extend their vase life. In their study, Krzymińska-Bródka and co-authors [5] also found no beneficial effect of 8HQS on prolonging the vase life of P. multiflorum leaves, while other studies showed a negative effect of this substance on the longevity of Viola odorata leaves [37] and Sedum spectabile inflorescences [38]. Other studies, on the other hand, demonstrate the positive effect of 8HQC + 2%S used as a conditioner on the durability of cut leaves. A fas in Waldsteinia geoides [1], Gerbera jamesonii [39], Lathyrus odoratus [40], Allium [41], and Antirrhinum majus [42].

A decrease in chlorophyll content is one of the first visual signs of leaf senescence [28]. During leaf aging, a decrease in chlorophyll content is evident, while carotenoid degradation proceeds much more slowly [43]. The phenomenon of chlorophyll degradation observed during the progressive ageing of leaves is completely natural, but unfavorable from the point of view of the floristic value of cut greens, so all post-harvest treatments are aimed at inhibiting it. Some studies confirm the beneficial effect of plant hormones, including gibberellins, on the inhibition of chlorophyll decline in the leaves of cut greens, including Ethiopian calla [36], Lilium longiflorum [44], and Alstroemeria [45].

Our research showed that in both the analyzed species, conditioning in GA₃ solution had a more favorable effect on the inhibition of chlorophyll degradation in the cut leaves. After 28 days of the experiment, the highest chlorophyll a and b concentrations were determined in the Hosta leaves treated with GA₃ at a concentration of 200 mg L⁻¹, whereas this was determined for the P. multiflorum leaves treated with GA₃ solution at a concentration of 400 mg L⁻¹. The positive effect of conditioning cut leaves in GA₃ solution on the inhibition of chlorophyll degradation has been confirmed in studies by Janowska and Schroeter-Zakrzewska on Limonium latifolium [46], as well as by Skutnik and co-authors [27] and Janowska and Stanecka on Zantedeschia [47]. Also, Janowska and co-authors [18] confirmed that the conditioning of Hemerocallis x hybrida, Limonium latifolium, and Heuchera hybrida leaves in GA₃ solution resulted in higher chlorophyll contents during the storage period compared to those of the control. The authors noted that the lack of chlorophyll degradation in leaves is not always correlated with the longest vase life of cut leaves. They explain that the observed phenomenon may be caused by other chlorophyll degradation mechanisms that are initiated in leaves, which are observed in stay-green plants. According to Nakajima et al. [48], the increased persistence of chlorophylls in their leaves is correlated with the delayed detachment of the light-harvesting complex of photosystem II. This results in the slower conversion of chlorophyll b to chlorophyll a and a decrease in the substrate availability for pheophorbide a oxygenase.

In the current experiment, all the substances used for conditioning led to a larger reduction in carotenoid degradation in the Hosta and P. multiflorum leaves compared to that of the control. A high content of these pigments in the Hosta leaves after 28 days of the experiment was determined in variants in which all the concentrations of BA and GA₃ and the commercial preparation Chrysal Clear 2 were applied. In contrast, in the leaves of P. multiflorum, the best effect was obtained in the variants in which the leafy stems were conditioned at the highest BA concentration, all the GA₃ concentrations, and in Chrysal Clear 2 solution. The inhibition of carotenoid degradation as a result of conditioning Weigela florida leaves in BA and GA₃ solutions was also observed by Rubinowska and co-authors [43]. Carotenoids, due to the presence of conjugated double bonds, can act as free radical scavengers, increased amounts of which are observed during the ageing of cut plant material. They also react with singlet oxygen and organic radicals formed by the peroxidation of membrane lipids [49].

Changes in the anthocyanin content in the Hosta and P. multiflorum leaves were also observed throughout the experiment. The highest concentration of pigments was seen in the Hosta leaves conditioned in 8HQC + 2%S and Chrysal Clear 2 solution, as well as in the P. multiflorum leaves conditioned in 8HQC + 2%S solution. The phenomenon of leaves turning a darker color during storage, which is associated with excessive anthocyanin accumulation, has been previously described and linked to the use of sucrose as an additive to the conditioning medium [50]. The presence of sugar in the nutrient solution can cause excessive sugar accumulation in the leaves and the consequent onset of osmotic stress, the symptom of which is the darkening and drying of the leaves [51]. Han [52], on the other hand, suggests that leaf darkening may be caused by a phytotoxic reaction to excess sugars in the nutrient solution. The stimulatory effect of sucrose on the increase of anthocyanin synthesis in leaves has been previously described in various plant species [53,54,55].

During the storage of cut plant material, a decrease in fresh weight is observed, which is the result of cutting the leaves or leafy shoots from the parent plant. Weight loss in cut foliage is associated with water potential imbalances and respiratory metabolism caused by improper water conductance, which may be caused by xylem vessel occlusion, air embolism, or increased leaf transpiration [19,56]. Insufficient water uptake by leaves cut off from the parent plant due to occlusion is one of the main causes of the insufficiently long vase life of cut greens. Among the causes of xylem occlusion, microbial colonization, the accumulation of gums and mucilage in the lumen of xylem vessels, the formation of tyloses, and the presence of the air emboli in the vascular system are mentioned [56].

Water stress during storage has been shown to accelerate leaf aging, including chlorophyll degradation [57]. In contrast, Wachowicz and co-authors [20], investigating Hosta leaf longevity, found that water stress had no direct effect on the senescence of cut leaves. In the current experiment, a beneficial effect of conditioning the Hosta leaves in GA₃ solutions at concentrations of 200 and 400 mg L⁻¹ and in Chrysal Clear 2 on the RWC values was found. In contrast, the leafy shoots of P. multiflorum responded most favorably to conditioning in GA₃ solution at a concentration of 400 mg L⁻¹. The positive effect of GA₃ on inhibiting the loss of fresh leaf mass during storage, and thus impeding transpiration was confirmed by Bunya-Atichart and co-authors [58] in studies on Curcuma alismatifolia and by Janowska and Schroeter-Zakrzewska [59] and Danaee and co-authors [60] in studies on Arum italicum and Gerbera jamesonii. In contrast, Krzymińska-Bródka and co-authors [5] found no significant changes in the fresh weight of P. multiflorum leaves conditioned in GA₃ solution compared to that of the control plants. A more positive effect of the conditioning of Weigela florida leafy shoots in Chrysal Clear 2 solution on the RWC compared to that of the control has been reported by Rubinowska and co-authors [43], as well as by Koziara and Suda [61] in a study on cut leaves of Cordyline ‘Glauca’. Chrysal Clear 2 contains sucrose, as well as bactericidal and fungicidal components, thus reducing the water stress related to cutting leaves from the parent plant [43,62].

The senescence of cut leaves also results in the loss of integrity of the cytoplasmic membranes due in part to an uncontrolled increase in free radical formation and the auto-oxidation of cell organelles [63]. The breakdown of cell membranes is stimulated by an increase in the activity of enzymes involved in the catabolism of membrane lipids [64]. Our analyses of the electrolyte leakage parameter showed that the conditioning of the Hosta leaves in BA solution regardless of the concentration and in GA₃ solution at 100 and 200 mg L⁻¹ significantly affected the stability of the cytoplasmic membranes. However, in the P. multiflorum leaves, a significant reduction in the E_L values compared to those of the control was found for all the conditioning variants used in the experiment.

The TBARS analysis, which determines the degree of membrane lipid peroxidation, of the Hosta leaves after 28 days of the experiment indicated the most beneficial effect of BA at concentrations of 100 and 200 mg L⁻¹, while this was found in the P. multiflorum leaves treated with BA and GA₃ at a concentration of 100 mg L⁻¹. The positive effect of conditioning cut Peonia lactiflora leaves in BA and GA₃ solutions on reducing the E_L index was reported by Michałek and co-authors [65]. The authors explain the effectiveness of these cytokinins on inhibiting cytoplasmic membrane degradation by their ability to trap and neutralize free radicals. In contrast, the beneficial effects of conditioning cut leaves in GA₃ solution on maintaining the stability of cytoplasmic membranes in cut leaves of Weigela florida were found by Rubinowska and co-authors [43] and Michalek and co-authors [65] for leaves of Peonia lactiflora. A study by Gaur and co-authors [66] confirms the beneficial effects of GA₃ and BA on reducing membrane lipid peroxidation and electrolyte leakage, and consequently on extending the post-harvest vase life of Gladiolus grandiflorus shoots. Other studies on cut flowers show that conditioning in GA₃ solution increases the activity of antioxidant enzymes [67,68], resulting in higher values of the membrane stability index and having a protective effect on cell organelles, including the mitochondria, the vacuoles, and the chloroplasts [69].

5. Conclusions

The leaves of Hosta and the shoots of P. multiflorum reacted to the ongoing aging process with disturbances in water management, a decrease in the integrity of the cytoplasmic membranes, and a reduction in the contents of plant pigments, including chlorophyll a, and b, carotenoids, and anthocyanins. The prolongation of the vase life of the cut leaves and shoots of the studied species in the selected variants of the experiment by up to 30 days is a satisfactory result, which makes it possible to qualify them as species suitable for use in floral compositions. Although interesting results were obtained, demonstrating the great potential for extending the longevity and improving the appearance of cut plants, unfortunately it was not possible to identify a single substance that would increase the durability of the tested raw materials, and at the same time, have a beneficial effect on all the analyzed parameters, assessing the aging process of the tested plant material. BA appeared to be the most effective in extending the post-harvest vase life for both the plants, while GA₃ appeared to be universal in terms of inhibiting pigment degradation. The only difference was in the concentrations that produced the best effect for the individual substances tested in the current study. In no aspect was 8HQC + 2%S more effective than the other substances, so it appears to be the least beneficial of the conditioning solution components tested.

Finding the optimum conditions for the storage and use of cut plants (including the composition of conditioning solution) is important from economic and ecological points of view. Universal substances that would have a positive effect on various aspects that lead to the progression of tissue degradation, and thus could extend the usability of the plant material, hold the greatest application value. The commercially available products used in the experiment did not prove to be the most effective, which shows that the search for better and more universal conditioning substances is still necessary.