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Article

Petal Morphology Is Correlated with Floral Longevity in Paeonia suffruticosa

by
Yingzi Guo
1,2,†,
Yongjie Qiu
1,†,
Huan Hu
1,
Yanli Wang
1,
Zhaorong Mi
1,
Shulin Zhang
1,
Songlin He
1,2,* and
Wenqing Jia
1,*
1
College of Horticulture and Landscape Architecture, Henan Institute of Science and Technology, Xinxiang 453003, China
2
College of Landscape Architecture and Art, Henan Agricultural University, Zhengzhou 450002, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work and are co-first authors.
Agronomy 2023, 13(5), 1372; https://doi.org/10.3390/agronomy13051372
Submission received: 28 March 2023 / Revised: 10 May 2023 / Accepted: 11 May 2023 / Published: 14 May 2023
(This article belongs to the Special Issue Flowering and Flower Development in Plants)
Browse Figures
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Abstract

:
Floral longevity (FL) is an important floral functional trait which is critical for flowering plants. FL shows great diversity among angiosperms; however, there is limited information on the mechanisms that influence differences in floral longevity, especially the relationship between petal anatomical traits and floral longevity. We aimed to examine (1) the relationships between petal anatomical traits and FL in tree peony cultivars and (2) the petal anatomical characteristics of longer FL cultivars. Eleven traits of six tree peony cultivars with different FL were investigated, including six water conservation traits (petal thickness, cuticle thickness, number of cell layers, mesophyll thickness, adaxial epidermis thickness and abaxial epidermis thickness), three water supply traits (vein density, number of xlylem vessels and xylem vessel diameter), petal fresh mass and petal dry mass across cultivars. There are significant differences in traits related to water conservation and water supply ability of tree peonies with different FL. Tree peony cultivars with long FL were characterized by the thicker Mesophyll, cuticles, adaxial and abaxial epidermis of the petals. There was a positive correlation between FL and vessel number and vessel diameter. These results suggest that the ability to retain water in flowers is associated with floral longevity. Petal traits related to water conservation and supply, including vein densities, mesophyll thickness, and epidermis thickness, are beneficial for prolonging the flower longevity in tree peonies.

1. Introduction

Floral longevity (FL), the period of time between anthesis and floral senescence, plays an important role in the ornamental value of flowering plants. A longer duration of the flowering not only enhances the ability of plants to attract pollinators, but also significantly increases their ornamental appearance, which is critical for ornamental crops. The FL trait shows great diversity in angiosperms [1]. For example, the flowers of Epiphyllum oxypetalum and Oenothera spp. remain open for only a few hours, while other species, such as Phalaenopsis aphrodite and Cattleya × hybrida, can last for weeks or even several months [1,2,3]. The factors that affect floral longevity have been a focus of recent theoretical and empirical research [1,2,3,4].
Previous studies have found that FL is closely related to biotic and abiotic factors [5,6,7,8,9,10,11,12]. In many flowering plants, flowering senescence is triggered by pollination. Premature artificial or insect pollination shortens FL [11,12,13], which may be an adaptive trait that minimizes water loss and resource expense incurred by maintaining open flowers [14,15].
FL depends on temperature and water balance and is affected by floral respiration and transpiration [2,16]. A previous study on cut flower preservation found that preservative application can improve the water balance of cut flowers, maintain petal swelling pressure, and extend the life of cut flowers [17]. Oblique trimming or recutting of the stems can increase the water absorption efficiency of cut flowers and prolong FL [18]. Reducing temperature and the content of carbon dioxide and oxygen in the air can reduce plant respiration, thereby slowing down the rate of energy and water loss [19]. For example, hemerocallis (daylily) flowers, affected by temperature, usually last one day and bloom for two days in September and three days in late October [20].
The balance of water in petals is closely related to the epidermal features and anatomical traits of plant petals. Long FL is basically accompanied by thicker adaxial and abaxial epidermis of the flower, and tightly coupled with water conservation in flowers [21]. Cuticle as one of epidermal features not only minimizes water loss and provides protection against desiccation, but also has a role in plant development and environmental interactions [22]. For example, Kirsch et al. [23] reported that species with short leaf longevity have relatively thin cuticles, while species where foliage has a longer leaf longevity tend to possess relatively thicker/denser cuticles with a more robust leaf to maximize net photosynthesis [24]. Flower dry mass is also strongly and positively related to drought tolerance of the flowers and FL [25]. Zhang et al. conducted a systematic study and concluded that there was a positive relationship between FL and floral dry mass per unit area in 11 species of Paphiopedilum (slipper orchids) [26]. An adequate water supply is needed during all periods of floral display [27,28,29]. Therefore, understanding the relationship between the floral water transport system (xylem vessels in veins) and FL may provide new insights into the evolution of flowers [30,31,32]. At present, studies on longevity in plants focus only on the functional link between leaf longevity and morphology, whereas the mechanisms that influence the FL difference between longer-FL and shorter-FL plants are still unclear.
Tree peony (Paeonia sect. Moutan) is well known for its high ornamental value, with approximately nine species, two subspecies, and more than 1500 cultivars [33]. Our long-term observation showed that most cultivars of tree peonies with very thin and soft petals have a flowering period of only 3–5 days, but some cultivars with hard petals have a flowering period of 8–10 days. The differences in FL, morphology, habitat, and physiology between long FL cultivars and shorter FL cultivars make them ideal candidates for exploring the association between FL and petal structure in tree peonies.
The current study explores the relationship between epidermal characteristics, anatomical structures and tree peony FL and examines three questions regarding tree peony FL and petal characteristics: (i) Could epidermal cuticle and thickness be associated with FL? It can be hypothesized that that the presence of the epidermal cuticle is associated with a long floral life. (ii) Do cultivars with a higher number of petal cell layers have longer FL? One may expect that petals with a high number of cell layers, which have an enhanced water retention capacity, have a longer FL than petals of cultivars with a low number of cell layers. (iii) Do petal flowers with dense veins and well-developed vascular bundles live longer? It can be hypothesized that petals with denser vasculatures and well-developed vascular bundles have increased FL due to their enhanced ability to transport water, which helps maintain water balance within the petals. The aim of this paper was to investigate the floral structural traits related to water balance and six tree peony FL and to explore the related mechanism that affects the differences in FL between six tree peonies.

2. Materials and Methods

2.1. Study Site and Species

FL and other floral traits (Table 1) were observed for three cultivars with longer FL (‘Souvenir de Maxime Cornu’, ‘Haihuang’, ‘Changshoule’) and three cultivars with shorter FL (‘Sihelian’, ‘Zhihong’ and ‘Shanhutai’). Six decade-old tree peony cultivars with different FLs (Figure 1) were planted in the National Peony Garden (112°41″ E, 34°71″ N) in Luoyang city. The weather conditions during the observation and sampling periods were as follows: the highest daily average temperature was 19 °C and the lowest was 10.4 °C, wind speed < 10 km/h with no precipitation.
The experiments were carried out at the Henan Horticultural Plant Resources Innovation and Utilization Engineering Research Center in April 2021. The surfaces of epidermal cells on the petals were examined by scanning electron microscopy (SEM). The cross-sectional anatomy of the petals was prepared following the method detailed by Chavarria et al. [34] and Olsen et al. [35] and visualized under a light microscope (LM) [36,37,38]. Several anatomical characteristics including petal thickness, number of petal cell layers, cuticle thickness, mesophyll thickness, adaxial epidermal thickness, abaxial epidermal thickness, and vessel diameter were measured with the help of the Olympus cellSens standard software [37].

2.2. Flower Longevity

The floral longevity was defined from the beginning of the petals opening slightly and exposing the stamens to the wilting or abscission of the petals. To investigate the FL of a single flower for each cultivar, 8–10 newly emerging floral buds we randomly selected of 3–5 plants per cultivar over three consecutive years (2018–2020). Their individual opening and wilting dates were recorded throughout the flowering season.

2.3. Fresh Weight and Dry Weight of Petals

A 4 cm × 4 cm sample was taken from midway between the midrib and the margin of five petals per species, and the fresh mass of the samples was recorded. Subsequently, these samples were oven-dried at 70 °C for 48 h to obtain petal dry mass [26,39].

2.4. Scanning Electron Microscope

For scanning electron microscope observation, the fragments of about 5 mm × 5 mm were taken from the central part of each tree peony petal and glued to the sample table with double-sided black conductive tape without any treatment. The samples were sputtered with gold–palladium. Then, the micromorphological details (stomata, sculptures, and epidermal cells) of samples were observed and photographed under a scanning electron microscope (Quanta 200, FEI Corporation, Hillsboro, OR, USA). The analysis of epidermis sculptures involved the observation and description of the epidermal cells, calculated following the method of Zhou et al. [40].

2.5. Light Microscope

Fragments of 1 cm2 were cut from the central part of the outer whorl petals and soaked in distilled water to avoid rapid dehydration. Subsequently, the fragments were cut into 0.1–0.3 mm fragments quickly along the direction perpendicular to the texture of the petal epidermal with razor blade. These fragments were placed in a drop of water on a slide, covered with cover slides, and later observed under a microscope (BX53, Olympus, Tokyo, Japan).
The fragments in the same batch were fixed in formalin–acetic acid–alcohol (FAA) fixing solution (5% formaldehyde, 5% acetic acid and 70% alcohol) at 4 °C for three days, and then rinsed with distilled water for 24 h. The samples were then dehydrated in 50%, 70%, 90%, 95% and 100% graded ethanol solutions, infiltrated in the mixtures of anhydrous ethanol and dichloromethane (3:1, 1:1, 1:3 [V]: [V]) and embedded in a mixed solution of dichloromethane and paraffin wax (3:1, 1:1, 1:3 [V]: [V]). For observations of the anatomical structure of petals, thin (10 μm) sections were obtained using an RM2245 semiautomatic rotary microtome (Leica Microsystems, Nussloch, Germany). These paraffin sections were stained with safranin and fast green dye [41], and observed and photographed under a fluorescence microscope (BX53, Olympus, Tokyo, Japan). Petal thickness, cuticle thickness, adaxial epidermal thickness, abaxial epidermal thickness, and mesophyll thickness of the petals were determined with the help of the Olympus cellSens standard software 1.12 [37]. Vein density was measured as the total length of the vascular tissue per mm2 of petal surface area. The xylem vessel number of each cultivar was the mean of the xylem vessels in 18 veins. Xylem vessel diameter was determined as the average of 18 randomly selected xylem vessel diameters.

2.6. Statistical Analysis

To assess the stability of micromorphological details, three petals per flower, two flowers per bush and three bushes per cultivar were analyzed. Petal micromorphology data are the average of at least 18 replicates. The correlation among variables was statistically evaluated using Pearson’s correlation coefficient (r) at a p value of 0.05. Duncan’s multiple comparisons were used to evaluate the differences in petal micromorphology of six cultivars of tree peonies at a 95% confidence interval (p < 0.05). The classification of six tree peony cultivars with different FL was determined based on petal traits using the Principal Component Analysis (PCA) method. Differences in floral traits among six tree peony cultivars were determined by the Mann–Whitney U test. All statistical analyzes for petal traits were performed with the SPSS 19.0 software (SPSS Inc., Chicago, IL, USA). All figures were drawn using the SigmaPlot 14.0 software.

3. Results

3.1. Flower Longevity

The length of FLs in different cultivars of tree peonies was significantly different (p < 0.05) (Table 1). The longest floral longevity was recorded in ‘Haihuang’ and the shortest was recorded in ‘Zhihong’.

3.2. Epidermal Morphological Characteristics of Petals

The size and shape of epidermal cells varied among the six cultivars. Epidermal cells viewed from above in three cultivars with long FL exhibited an elongated cell shape, and the epidermal cells were arranged in parallel, with a larger cell area (Figure 2A–C and Figure 3A–C). Rectangular cell shapes were observed on the epidermis of ‘Sihelian’, ‘Zhihong’ and ‘Shanhutai’, especially in the adaxial direction (Figure 2D–F). The pattern of anticlinal cells was straight to curved in all studied cultivars.
Consistent with our hypothesis, the surface of the epidermis was covered with smooth (Figure 4B) or sculpted cuticles (Figure 5D,E) to various degrees. Within the observed cultivars, we recognized two types of epidermal cuticle. The smooth parallel filamentous cuticle was present on the outer surfaces of the petal epidermal cells in ‘Haihuang’, ‘Souvenir de Maxime Cornu’ and ‘Changshoule’ (Figure 4A,C) [42]. The curly and rough cuticle was recorded in ‘Shanhutai’, ‘Sihelian’ and ‘Zhihong’ (Figure 4D). The texture of graininess was present on both surfaces of ‘Sihelian’, ‘Zhihong’, and ‘Shanhutai’, but absent in ‘Souvenir de Maxime Cornu’, ‘Haihuang’, and ‘Changshoule’. This diversity is particularly evident on the abaxial surface (Figure 5).
The adaxial and abaxial epidermis are covered with cuticle (Figure 6). The thickest cuticle on the adaxial surface was observed in ‘Jinge’, followed by ‘Haihuang’ and ‘Changshoule’, and the thinnest cuticle was recorded in ‘Shanhutai’. The thickest cuticle was observed on the abaxial surface in ‘Haihuang’, while the thinner cuticle was found on the epidermis of ‘Sihelian’, ‘Zhihong’ and ‘Shanhutai’. Overall, the cuticle on the adaxial and abaxial epidermis of the petals with long FL was significantly thicker than that in petals with shorter FL (Table 2).
No stomata were found on either surface of the petals in all examined cultivars (Figure 4 and Figure 5).

3.3. Analysis of the Petal Cross-Sectional Anatomy

Petal thickness, cuticle thickness, and number of cell layers differed significantly (p < 0.05) among the studied cultivars (Table 2). The thickest petal (198.1 μm) was found in ‘Haihuang’, and the thinnest (75.3 μm) was in detected ‘Zhihong’, whereas the maximum petal cuticle thickness (11.8 μm) was reported in ‘Souvenir de Maxime Cornu‘ and the minimum (1.6 μm) was reported in ‘Zhihong’ (Table 2). Consistent with our prediction, the number of petal cell layers of the three long-flowering tree peony cultivars (‘Haihuang’, ‘Souvenir de Maxime Cornu’ and ‘Changshoule’) was significantly higher (p < 0.05) than that of the three short-flowering tree peony cultivars (‘Sihelian’, ‘Zhihong’ and ‘Shanhutai’).
The petal mesophyll of the six tree peony cultivars was loosely arranged with many intercellular spaces with mesophyll thickness ranging between 50.4 and 142.3 μm (Figure 6, Table 2). The mesophyll thickness in the cultivars with long FL was significantly higher than in the cultivars with shorter FL. The values for mesophyll thickness of the petals did not differ significantly between cultivars with shorter FL (Table 2).
Veins (vascular bundles) were found in all of the observed tree peony cultivars. The mean density of the vein varied from 1.4 to 2.6. The maximum vein density was recorded for ‘Haihuang’ (2.6 per mm2), followed by ‘Souvenir de Maxime Cornu’ (2.3 per mm2) and the minimum in ‘Zhihong’ (1.4 per mm2). The vessel number per vascular bundle and vessel diameter varied significantly (p < 0.05) with different tree peony cultivars (Table 2, Figure 7). The largest vessel number (12.2) was found in ‘Changshoule’, and the lowest number (5.6) was in ‘Zhihong’, while the maximum vessel diameter (7.8 μm) was reported in the ‘Souvenir de Maxime Cornu’ and the minimum (3.9 μm) in ‘Shanhutai’ (Table 2, Figure 7). The cultivars with long FL differed significantly from the cultivars with shorter FL in vein density, vessel number, and vessel diameter (p < 0.05).
Among the six examined tree peony cultivars, we found broad range of diversity in the petal dry mass and the petal fresh mass. The maximum petal dry mass was reported in ‘Haihuang’ with 4.2 mg/cm2, followed by the ‘Souvenir de Maxime Cornu’ with 4.0 mg/cm2, and the minimum petal dry mass was recorded in ‘Shanhutai’, whereas the maximum petal fresh mass (24.6 mg/cm2) was reported in ‘Souvenir de Maxime Cornu’ and the minimum (12.9 mg/cm2) was reported in ‘Zhihong’ (Table 2).

3.4. The Correlations between Water-Related Traits and Floral Longevity

Table 3 shows that significant relationships were found among traits associated with FL, petal dry mass, petal fresh mass, and flower maintenance. FL was significantly positively correlated with petal dry mass, petal fresh mass, mesophyll thickness, and vein density (p < 0.05), but not with xylem vessel number (Table 3). We also observed a significantly positive correlation between petal dry mass and petal fresh mass (p < 0.05).

3.5. Principal Component Analysis

The principal component analysis demonstrated that the first two components comprised 70.4% and 15.5% of the total variation, respectively (Figure 8). Variables that correlated mainly with component 1 were petal fresh mass, petal dry mass, abaxial epidermis thickness, adaxial epidermis thickness, and petal thickness. The parameters such as vessel number, number of cell layers and vein density were mainly positively loaded on component 2, while vessel diameter, petal fresh mass, petal dry mass, and cuticle thickness were negatively loaded on component 2. Species-loadings showed that the three tree peony cultivars, ‘Haihuang’, ‘Souvenir de Maxime Cornu’ and ‘Changshoule’ were grouped on the positive side, while Shanhutai’, ‘Sihelian’ and ‘Zhihong’ clustered on the negative side, indicating that there was a significant difference in flower traits between cultivars with long FL and one with short FL. Scatter plots are often helpful in detecting patterns of variation, and as can be seen in the plot (Figure 8), the first and second components help to distinguish between long- and short-FL tree peony cultivars.

4. Discussion

Using six tree peony cultivars with different FL, we examined the relationships between FL and petal anatomical traits. The principal novel findings of our study are the following: (1) long FL is closely coupled with the petal traits related to water conservation in tree peonies, such as mesophyll thickness, epidermis thickness, cuticle thickness, and no stomata; (2) the petals of the tree peony cultivars with long FL are basically accompanied by developed conducting tissues. These results suggest that most petal traits related to water conservation and supply, including the vein density, mesophyll thickness, and epidermis thickness, are closely related to floral longevity in the tree peonies, as demonstrated in orchid species [21].
Reducing water loss is important to maintain the water balance of whole plants and the flower turgor. Stomatal transpiration and cuticular transpiration are the two main pathways for water loss in flowers, leaves, and fruits [43,44,45]. Cuticular barriers play a key role in protecting plants against water loss in organs with closed stomata or no stomata [46]. The epidermis, including epidermal cells and epidermal cuticle, acts as a protective layer for water conservation, and its thickness is closely related to the lifespan of the flower or leaf; thicker epidermis was more tolerant to drought stress [37,47,48]. Zoran Ristic et al. [49] reported that there is an inverse relationship between epidermal water loss and cell wall and cuticle thickness [50]. The epidermal cuticle of plant organs can greatly reduce excessive water evaporation by plant cells [51,52,53]. Studies have shown that plant cuticular wax has diverse crystal structures [54] and the content, distribution and size of wax crystals greatly influence water loss [55,56]. In addition, the smooth parallel filamentous cuticular wax layer can reflect sunlight to avoid the rise of leaf temperature and reduce radiation damage [57]. Our results showed that the petals of a flower with long FL were covered by thicker cuticle on the surface of the epidermis, while the cuticle of the petals of flowers with shorter FL is sparsely sculpted in curls. Furthermore, FL was significantly associated with epidermal and mesophyll thickness. This indicated that thicker epidermal cells and cuticular layer provide the ability of petal epidermis to function as a hydrophobic barrier, which in turn prolongs the FL of tree peony. The smooth parallel filamentous wax layer of long FL petals can reduce the radiation of sunlight to reduce water loss. There are no stomata on the petals of tree peonies. Tree peony cultivars with petals containing veins but without stomata represent an obvious case in which vein–stomatal coordination was absent. These findings are consistent with the results previously reported in leaves and flowers of different plant species [26,51,58,59], indicating that FL may be determined by water conservation and storage. Therefore, the improvement in FL of tree peony occurs mainly due to the reduction in the water loss of the flower and the improvement of the water storage capacity.
The high leaf dry mass is typical of stress-tolerant species [60,61]. Leaf dry mass correlates with water transport and utilization, and leaves with longer lifespan usually have higher dry mall per unit area [62]. High LMA is generally associated with greater drought resistance [60,61]. Our results showed that the FMA of the tree peony cultivars with longer FL was significantly higher than that of cultivars with shorter FL, indicating that FL is evolutionarily correlated with flower dry mass per unit area (Figure 3). This relationship seems to mirror a critical indicator of plant adaptive strategies [61].
In leaves and petals, water supply (vein density, number and diameter of vessels) and water storage are usually coordinated with water loss to keep the water balance [63,64,65,66]. Xylem vessels participate in the water transport and supply of water [59]. The size of the vascular bundle and the number of its vessels affect the conduction efficiency of plants [58]. We found the large diversity in petal vein density in the examined cultivars. Long FL was often accompanied by a greater number of vessels and a larger vessel diameter, probably suggesting that the flower with long FL has strong water supply capacity which can effectively meet the water requirements to maintain the petal turgor.
FL diversity usually reflects the adaptation of plants to their habitats [9,10,50]. Species with short FL usually bloom in weather conditions suitable for pollinator visiting, while species with long FL open in the environments that are not suitable for pollinator visiting [67,68]. Long FL can compensate for the lack of pollinators and improve reproductive success [14]. Tree peonies usually bloom in spring when pollinators could visit their flowers, which may be one of the explanations for the shorter blooming period of the six examined tree peony cultivars compared to Paphiopedilum [21].

5. Conclusions

Our results supported the hypothesis that the cost of maintaining floral function measured by the floral anatomical traits is correlated with FL. The floral anatomical details related to water conservation and water storage capacity including the number of layers of petal cells, the thickness of cuticle and epidermis, and the mesophyll thickness are beneficial in prolonging the flower longevity in tree peonies. In addition, the tree peony cultivars with longer FL have more developed vascular tissue, which can be more efficient in transporting the water and other nutrients needed to maintain the flower life. Our findings provided strong evidence for a functional association between FL and water conservation and supply capacity in tree peonies.

Author Contributions

Formal analysis, Y.G., W.J. and Y.Q.; investigation, Y.G., W.J., Y.W., Z.M., H.H. and S.H.; resources, W.J. and S.H.; data curation, Y.G., W.J. and Y.Q.; writing—original draft preparation, Y.G., W.J., S.Z. and Y.Q.; writing—review and editing, W.J. and S.H.; visualization, H.H.; project administration, W.J. and S.H.; funding acquisition, W.J. and S.H. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by the National Key Research and Development Program of China (2018YFD1000401), Henan Provincial Science and Technology Plan Project (232102111107) and Zhongyuan Talent Plan Project (ZYYCYU202012129).

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Flowers of six tree peony cultivars. (A) ‘Souvenir de Maxime Cornu’; (B) ‘Hahuang’; (C) ‘Changshoule’; (D) ‘Sihelian’; (E) ‘Zhihong’; (F) ‘Shanhutai’.
Figure 1. Flowers of six tree peony cultivars. (A) ‘Souvenir de Maxime Cornu’; (B) ‘Hahuang’; (C) ‘Changshoule’; (D) ‘Sihelian’; (E) ‘Zhihong’; (F) ‘Shanhutai’.
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Figure 2. Top view of the abaxial epidermis of the petals of the six tested tree peony cultivar samples. (A) ‘Souvenir de Maxime Cornu’; (B) ‘Haihuang’; (C) ‘Changshoule’; (D) ‘Sihelian’; (E) ‘Zhihong’; (F) ‘Shanhutai’. Bar = 50 μm.
Figure 2. Top view of the abaxial epidermis of the petals of the six tested tree peony cultivar samples. (A) ‘Souvenir de Maxime Cornu’; (B) ‘Haihuang’; (C) ‘Changshoule’; (D) ‘Sihelian’; (E) ‘Zhihong’; (F) ‘Shanhutai’. Bar = 50 μm.
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Figure 3. Top view of the adaxial epidermis of the petals of the six tested tree peony cultivar samples. (A) ‘Souvenir de Maxime Cornu’; (B) ‘Haihuang’; (C) ‘Changshoule’; (D) ‘Sihelian’; (E) ‘Zhihong’; (F) ‘Shanhutai’. Bar = 50 μm.
Figure 3. Top view of the adaxial epidermis of the petals of the six tested tree peony cultivar samples. (A) ‘Souvenir de Maxime Cornu’; (B) ‘Haihuang’; (C) ‘Changshoule’; (D) ‘Sihelian’; (E) ‘Zhihong’; (F) ‘Shanhutai’. Bar = 50 μm.
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Figure 4. Scanning electron micrographs of the abaxial epidermis of the petals of the six tested tree peony cultivar samples. (A) ‘Souvenir de Maxime Cornu’; (B) ‘Haihuang’; (C) ‘Changshoule’; (D) ‘Sihelian’; (E) ‘Zhihong’; (F) ‘Shanhutai’. Abbreviations: cu: cuticle; W: wax. Bar = 50 μm.
Figure 4. Scanning electron micrographs of the abaxial epidermis of the petals of the six tested tree peony cultivar samples. (A) ‘Souvenir de Maxime Cornu’; (B) ‘Haihuang’; (C) ‘Changshoule’; (D) ‘Sihelian’; (E) ‘Zhihong’; (F) ‘Shanhutai’. Abbreviations: cu: cuticle; W: wax. Bar = 50 μm.
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Figure 5. Scanning electron micrographs of the adaxial epidermis of the petals of the six tested tree peony cultivar samples. (A) ‘Souvenir de Maxime Cornu’; (B) ‘Haihuang’; (C) ‘Changshoule’; (D) ‘Sihelian’; (E) ‘Zhihong’; (F) ‘Shanhutai’. Abbreviations: cu: cuticle; W: wax. Bar = 50 μm.
Figure 5. Scanning electron micrographs of the adaxial epidermis of the petals of the six tested tree peony cultivar samples. (A) ‘Souvenir de Maxime Cornu’; (B) ‘Haihuang’; (C) ‘Changshoule’; (D) ‘Sihelian’; (E) ‘Zhihong’; (F) ‘Shanhutai’. Abbreviations: cu: cuticle; W: wax. Bar = 50 μm.
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Figure 6. Cross-sectional micrographs of petals of the six tree peony cultivars. (A) ‘Souvenir de Maxime Cornu’; (B) ‘Haihuang’; (C) ‘Changshoule’; (D) ‘Sihelian’; (E) ‘Zhihong’; (F) ‘Shanhutai’. Abbreviations: ad: adaxial epidermis; ab: abaxial epidermis; cu: cuticle; m: mesophyll cells. (Bar = 50 μm).
Figure 6. Cross-sectional micrographs of petals of the six tree peony cultivars. (A) ‘Souvenir de Maxime Cornu’; (B) ‘Haihuang’; (C) ‘Changshoule’; (D) ‘Sihelian’; (E) ‘Zhihong’; (F) ‘Shanhutai’. Abbreviations: ad: adaxial epidermis; ab: abaxial epidermis; cu: cuticle; m: mesophyll cells. (Bar = 50 μm).
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Figure 7. Cross-sections of petals from the six tree peony cultivars. (A) ‘Souvenir de Maxime Cornu’; (B) ‘Haihuang’; (C) ‘Changshoule’; (D) ‘Sihelian’; (E) ‘Zhihong’; (F) ‘Shanhutai’. Abbreviations: ad: adaxial epidermal cell; m: mesophyll; xy: xylem; cu: cuticle. Bar = 50 μm.
Figure 7. Cross-sections of petals from the six tree peony cultivars. (A) ‘Souvenir de Maxime Cornu’; (B) ‘Haihuang’; (C) ‘Changshoule’; (D) ‘Sihelian’; (E) ‘Zhihong’; (F) ‘Shanhutai’. Abbreviations: ad: adaxial epidermal cell; m: mesophyll; xy: xylem; cu: cuticle. Bar = 50 μm.
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Figure 8. Scatter plot based on the first component and the second component.
Figure 8. Scatter plot based on the first component and the second component.
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Table
Table 1. Floral traits and floral longevity of six Paeonia suffruticosa cultivars.
Table 1. Floral traits and floral longevity of six Paeonia suffruticosa cultivars.
CodeNameFlower ColorFlower TypeFL (Days)
1‘Souvenir de Maxime’ Cornu’Yellowish orangedouble-petaled8.5 ± 1.5 a
2‘Haihuang’Yellowsingle-petaled9.0 ± 1.2 a
3‘Changshoule’Light pinkdouble-petaled8.9 ± 1.1 a
4‘Sihelian’Pinksingle-petaled4.0 ± 1.1 b
5‘Zhihong’Rouge reddouble-petaled3.5 ± 1.5 b
6‘Shanhutai’Pinkdouble-petaled3.7 ± 1.3 b
Note: Data shown are average ± standard deviation. The data with different lowercase letter indicate significant differences at the 0.05 level, the same below.
Table
Table 2. Petal anatomical characteristics of the six tree peony cultivars.
Table 2. Petal anatomical characteristics of the six tree peony cultivars.
Traits‘Souvenir de Maxime Cornu’‘Haihuang’‘Changshoule’‘Sihelian’‘Zhihong’‘Shanhutai’
Petal thickness (μm)183.3 ± 10.9 ab198.1 ± 9.2 a188.9 ± 16.8 ab164.8 ± 8.3 b75.3 ± 5.1 d136.8 ± 8.2 c
Cuticle thickness (μm)11.8 ± 1.6 a4.2 ±0.6 c6.3 ± 0.5 b3.7 ± 1.2 cd1.6 ± 0.6 e2.6 ± 1.0 d
Number of cell layers10.5 ± 1.2 b11.3 ± 1.2 b18.2 ± 2.0 a8.3 ± 2.0 bc9.2 ± 2.0 bc9.0 ± 2.0 bc
Mesophyll thickness (μm)127.6 ± 3.8 ab142.3 ± 3.0 a137.0 ± 3.2 ab120.3± 1.8 b50.4 ± 1.2 d98.5 ± 3.5 c
Adaxial epidermis thickness (μm)23.5 ± 0.6 b26.7 ± 1.3 a22.7 ± 0.8 b19.7 ± 0.8 bc12.3 ± 0.6 d18.9 ± 3.5 c
Abaxial epidermis thickness (μm)20.3 ± 1.2 b25.4 ± 2.2 a22.1 ± 1.3 ab18.2 ± 2.1 bc11.0 ± 1.2 d16.7 ± 1.2 c
Vein density (mm/mm2)2.3 ± 0.2 a2.6 ± 0.21 a2.0 ± 0.3 ab1.6 ± 0.1 b1.4 ± 0.1 c1.5 ± 0.1 c
Vessel number per vein8.0 ± 1.00 b8.7 ± 0.6 b12.2 ± 0.10 a7.7 ± 1.15 bc5.6 ± 0.58 c7.9 ± 0.5 bc
Vessel diameter (μm)7.8 ± 0.2 a6.7 ± 0.25 b6.2 ± 0.4 b4.8 ± 0.5 c5.3 ± 0.3 c3.9 ± 0.2 d
Petal fresh mass (mg/cm2)24.6 ± 0.3 a23.8 ± 0.4 a19.8 ± 0.9 b16.0 ± 0.8 c12.9 ± 0.1 d13.5 ± 0.3 d
Petal dry mass (mg/cm2)4.0 ± 0.1 a4.2 ± 0.1 a3.5 ± 0.2 b3.0 ± 0.1 c2.4 ± 0.1 d2.2 ± 0.2 d
Note: Data shown are average ± standard deviation. Data with different lowercase letters in the same row indicate a significant difference at the 0.05 level.
Table
Table 3. Pearson’s correlations between water-related traits and floral longevity in tree peony cultivars.
Table 3. Pearson’s correlations between water-related traits and floral longevity in tree peony cultivars.
TraitsFloral LongevityPetal ThicknessCuticle ThicknessMesophyll ThicknessEpidermis ThicknessVein DensityVessel NumberVessel DiameterFresh WeightDry Weight
Floral longevity1
Petal thickness0.54 *1
Cuticle thickness0.40 *0.321
Mesophyll thickness0.82 **0.92 **052 *1
Epidermis thickness0.63 *0.94 **0.220.68 *1
Vein density0.81 **0.57 *0.54 *0.95 **0.50 *1
Vessel number per vein0.42 *0.51 *0.110.74 **0.43 *0.701
Vessel diameter0.74 **0.290.63 *0.76 **0.320.54 *0.071
Petal fresh mass0.80 **0.75 **0.43 *0.86 **0.82 **0.58 *0.230.73 **1
Petal dry mass0.79 **0.67 *0.42 *0.69 *0.73 **0.56 *0.200.78 **0.90 **1
Note: ‘*’ indicates significant differences (p < 0.05). ‘**’ indicates very significant differences (p < 0.01).
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Guo, Y.; Qiu, Y.; Hu, H.; Wang, Y.; Mi, Z.; Zhang, S.; He, S.; Jia, W. Petal Morphology Is Correlated with Floral Longevity in Paeonia suffruticosa. Agronomy 2023, 13, 1372. https://doi.org/10.3390/agronomy13051372

AMA Style

Guo Y, Qiu Y, Hu H, Wang Y, Mi Z, Zhang S, He S, Jia W. Petal Morphology Is Correlated with Floral Longevity in Paeonia suffruticosa. Agronomy. 2023; 13(5):1372. https://doi.org/10.3390/agronomy13051372

Chicago/Turabian Style

Guo, Yingzi, Yongjie Qiu, Huan Hu, Yanli Wang, Zhaorong Mi, Shulin Zhang, Songlin He, and Wenqing Jia. 2023. "Petal Morphology Is Correlated with Floral Longevity in Paeonia suffruticosa" Agronomy 13, no. 5: 1372. https://doi.org/10.3390/agronomy13051372

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